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Best Anatomical structure of All Time

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    1
    Ejaculatory duct

    Ejaculatory duct

    The ejaculatory ducts (ductus ejaculatorii) are paired structures in male anatomy. Each ejaculatory duct is formed by the union of the vas deferens with the duct of the seminal vesicle. They pass through the prostate, and open into the urethra at the Colliculus seminalis. During ejaculation, semen passes through the prostate gland, enters the urethra and exits the body via the tip of the penis. Ejaculation occurs in two stages, the emission stage and the expulsion stage. The emission stage involves the workings of several structures of the ejaculatory duct; contractions of the prostate gland, the seminal vesicles and the vas deferens push fluids into the bulbourethral glands. The semen is trapped here and it is at this point that males perceive to be the point of no return for orgasm. This may be more commonly known as a male feeling as though he is "about to come". This stage is followed by the expulsion stage. Muscles at the base of the penis contract in order to propel the seminal fluid trapped in the bulbourethral glands through the urethra and expel it through the tip of the penis. The ejaculate is expelled in spurts, due to the movement of the muscles propelling it. These
    7.00
    9 votes
    2
    Parotid gland

    Parotid gland

    The parotid gland is a salivary gland in humans. It is one of a pair, and the largest of the salivary glands. It is wrapped around the mandibular ramus, and secretes saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches. The word 'parotid' (paraotic) literally means around the ear. The parotid glands are a pair of serous salivary glands located below and in front of the external acoustic meatus draining their secretions into the vestibule of oral cavity through stensen's duct. They are the largest major salivary glands of the human body. Each gland lies posterior to the mandibular ramus and in front of the mastoid process of temporal bone. The gland is roughly wedge shaped when seen superficially and is also wedge shaped when seen on horizontal sections. The gland has a capsule of its own of dense connective tissue but is also provided with a false capsule by investing layer of deep cervical fascia. The fascia at the imaginary line between the angle of mandible and mastoid process splits into Superficial lamina and a deep lamina to enclose the gland. Risorius is a small muscle embedded with this capsules
    7.29
    7 votes
    3
    Calcaneus

    Calcaneus

    In humans, the calcaneus (from the Latin calcaneum, meaning heel) or heel bone is a bone of the tarsus of the foot which constitute the heel. In some other animals, it is the point of the hock. In humans, the calcaneus is the largest of the tarsal bones and the largest bone of the foot. In it, several important structures can be distinguished: The posterior half of the bone is the tuber calcanei. On its lower edge on either sides are its lateral and medial processes (serving as the origins of the abductor hallucis and abductor digit minimi). The Achilles tendon is inserted into a roughened area on its superior side, the cuboid bone articulates with its anterior side, and on its superior side are three articular surfaces for the articulation with the talus bone. Between these superior articulations and the equivalents on the talus is the tarsal sinus (a canal occupied by the interosseous talocalcaneal ligament). On the medial side of the bone, below the middle talar facet, is the sustentaculum tali (which serves for the attachment of several other ligaments). On the lateral side is commonly a tubercle called the peroneal trochlea, under which is a groove for the tendon of the
    7.67
    6 votes
    4
    Inferior vena cava

    Inferior vena cava

    The inferior vena cava (or IVC), also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart. It is posterior to the abdominal cavity and runs alongside of the vertebral column on its right side (i.e. it is a retroperitoneal structure). It enters the right atrium at the lower right, back side of the heart. The IVC is formed by the joining of the left and right common iliac veins and brings blood into the right atrium of the heart. It also anastomoses with the azygos vein system (which runs on the right side of the vertebral column) and venous plexuses next to the spinal cord. The caval opening is at T8. The specific levels of the tributaries are as follows: Because the IVC is not centrally located, there are some asymmetries in drainage patterns. The gonadal veins and suprarenal veins drain into the IVC on the right side, but into the renal vein on the left side, which in turn drains into the IVC. By contrast, all the lumbar veins and hepatic veins usually drain directly into the IVC. The tributaries of Inferior vena cava can be remembered using the mnemonic, "I Like To Rise So High",
    6.43
    7 votes
    5
    Esophagus

    Esophagus

    The esophagus (oesophagus) is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach. The word esophagus is derived from the Latin œsophagus, which derives from the Greek word oisophagos, lit. "entrance for eating." In humans the esophagus is continuous with the laryngeal part of the pharynx at the level of the C6 vertebra. The esophagus passes through posterior mediastinum in thorax and enters abdomen through a hole in the diaphragm at the level of the tenth thoracic vertebrae (T10). It is usually about 25cm, but extreme variations have been recorded ranging 10–50 cm long depending on individual height. It is divided into cervical, thoracic and abdominal parts. Due to the inferior pharyngeal constrictor muscle, the entry to the esophagus opens only when swallowing or vomiting. The layers of the oesophagus are as follows: Normally, the esophagus has three anatomic constrictions at the following levels; The distances from the incisor teeth are important as is useful for diagnostic endoscopic
    7.33
    6 votes
    6
    Oculomotor nerve

    Oculomotor nerve

    The oculomotor nerve is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the levator palpebrae superioris muscle. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement. The oculomotor nerve (CN III) arises from the anterior aspect of mesencephalon (midbrain). There are two nuclei for the oculomotor nerve: Sympathetic postganglionic fibres also join the nerve from the plexus on the internal carotid artery in the wall of the cavernous sinus and are distributed through the nerve, e.g., to the smooth muscle of levator palpebrae superioris. On emerging from the brain, the nerve is invested with a sheath of pia mater, and enclosed in a prolongation from the arachnoid. It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli. It runs along the
    8.40
    5 votes
    7
    Internal capsule

    Internal capsule

    The internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the putamen and the globus pallidus. The internal capsule contains both ascending and descending axons. It consists of axonal fibres that run between the cerebral cortex and the pyramids of the medulla. The internal capsule is V-shaped when cut horizontally/transversely (the same plane as the brim of a top hat). When cut horizontally: Working anterior to posterior: Other fibers within the internal capsule The superior parts of both the anterior and posterior limbs and the genu of the internal capsule are supplied by the lenticulostriate arteries, which are branches off of the M1 segment of the middle cerebral artery. The inferior half of the anterior limb is supplied via the recurrent artery of Heubner, which is a branch of the anterior cerebral artery. The inferior half of the posterior limb is supplied by the anterior choroidal artery, which is a branch of the internal carotid artery. In summary, the blood supply of the internal capsule is Anterior limb: lenticulostriate branches of middle cerebral artery (superior half) & recurrent artery of Heubner off of the
    7.17
    6 votes
    8
    Mesoderm

    Mesoderm

    In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm (outside layer) and endoderm (inside layer), with the mesoderm as the middle layer between them. The mesoderm forms mesenchyme (connective tissue), mesothelium, non-epithelial blood cells and coelomocytes. Mesothelium lines coeloms; forms the muscles, septa (cross-wise partitions) and mesenteries (length-wise partitions); and forms part of the gonads (the rest being the gametes). The mesoderm differentiates from the rest of the embryo through intercellular signaling, after which the mesoderm is polarized by an organizing center.
    9.50
    4 votes
    9
    Venae cavae

    Venae cavae

    The superior and inferior vena cava are collectively called the venae cavae. They are the veins that return deoxygenated blood from the body, into the heart. They both empty into the right atrium. The inferior vena cava (or caudal vena cava in animals) travels up alongside the abdominal aorta with blood from the lower part of the body (see # 11 in the diagram). It is the largest vein in the body. The superior vena cava (or cranial vena cava in animals) is above the heart, and forms from a convergence of the left and right brachiocephalic veins that contain blood from the head and the arms (see # 3 in the diagram).
    7.00
    6 votes
    10
    Cremaster muscle

    Cremaster muscle

    The cremaster muscle is a muscle that covers the testis. Its function is to raise and lower the testes in order to regulate the temperature of the testes and promote spermatogenesis. Contraction may also occur during arousal which can prevent injury to the testicles during sex. In a cool environment the cremaster draws the testis closer to the body and reduces surface area thereby reducing heat loss, while when it is warmer the cremaster relaxes allowing the testis to cool by increasing exposed surface area. Contraction can also occur during moments of extreme fear, possibly to help avoid injuring the testes while dealing with a fight or flight situation. Clinically, a reflex arc termed the cremasteric reflex can be demonstrated by lightly stroking the skin of the inner thigh downwards from the hip towards the knee. This causes the cremaster muscle on the same side to rapidly contract, raising that testicle. The cremaster can also be contracted voluntarily, by contracting the pubococcygeus muscle (using Kegels), or by sucking in the abdomen. The cremaster develops to its full extent only in males; in females it is represented by only a few muscle loops. In human females, the
    8.00
    5 votes
    11
    External carotid artery

    External carotid artery

    In human anatomy, the external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it bifurcates into the external and internal carotid artery. The external carotid artery begins at the level of the upper border of thyroid cartilage, and, taking a slightly curved course, passes upward and forward, and then inclines backward to the space behind the neck of the mandible, where it divides into the superficial temporal and maxillary artery within the parotid gland. It rapidly diminishes in size in its course up the neck, owing to the number and large size of the branches given off from it. In the child, it is somewhat smaller than the internal carotid; but in the adult, the two vessels are of nearly equal size. At its origin, this artery is more superficial, and placed nearer the middle line than the internal carotid, and is contained within the carotid triangle. The external carotid artery is covered by the skin, superficial fascia, Platysma, deep fascia, and anterior margin of the Sternocleidomastoideus; it is crossed by the hypoglossal nerve, by the lingual, ranine, common facial, and superior thyroid veins; and by the Digastricus and
    7.80
    5 votes
    12
    Rotator cuff

    Rotator cuff

    In anatomy, the rotator cuff (sometimes incorrectly called a "rotor cuff" or rotary cup) is a group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff are over half of the seven scapulohumeral muscles. The rotator cuff muscles are important in shoulder movements and in maintaining glenohumeral joint (shoulder joint) stability. These muscles arise from the scapula and connect to the head of the humerus, forming a cuff at the shoulder joint. They hold the head of the humerus in the small and shallow glenoid fossa of the scapula. The glenohumeral joint has been analogously described as a golf ball (head of the humerus) sitting on a golf tee (glenoid fossa). During abduction of the arm, moving it outward and away from the trunk, the rotator cuff compresses the glenohumeral joint, a term known as concavity compression, in order to allow the large deltoid muscle to further elevate the arm. In other words, without the rotator cuff, the humeral head would ride up partially out of the glenoid fossa, lessening the efficiency of the deltoid muscle. The anterior and posterior directions of the glenoid fossa are more susceptible to shear force
    7.80
    5 votes
    13
    Foramen ovale

    Foramen ovale

    At the base of the skull the foramen ovale (Latin: oval window) is one of the larger of the several holes (the foramina) that transmit nerves through the skull. The foramen ovale is situated in the posterior part of the sphenoid bone, posterolateral to the foramen rotundum. Several nerves, arteries and veins pass through the foramen ovale. They are as follows: The contents of this foramen neatly form the mnemonic 'OVALE' (otic ganglion, V3, accessory meningeal artery, lesser petrosal nerve, emissary veins) Similar to other foramina, the foramen ovale differs in shape and size throughout the natural life. The earliest perfect ring-shaped formation of the foramen ovale was observed in the 7th fetal month and the latest in 3 years after birth, in a study using over 350 skulls. In a study conducted on 100 skulls, the foramen ovale was divided into 2 or 3 components in 4.5% of the cases. The borders of the foramen in some skulls were also irregular and rough. This may suggest, based on radiological images, the presence of morbid changes, which might be the sole anatomical variation in the foramina ovale of humans. (Reymond et al.) In newborn, the foramen ovale is about 3.85 mm and in
    9.00
    4 votes
    14
    Pituitary gland

    Pituitary gland

    In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 grams (0.018 oz) in humans. It is not a part of the brain. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity (sella turcica) covered by a dural fold (diaphragma sellae). The pituitary is functionally connected to the hypothalamus by the median eminence via a small tube called the infundibular stem (Pituitary stalk). The pituitary fossa, in which the pituitary gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain. The pituitary gland secretes nine hormones that regulate homeostasis. The pituitary gland consists of two components: the anterior pituitary (or adenohypophysis) and the posterior pituitary (or neurohypophysis), and is functionally linked to the hypothalamus by the pituitary stalk (also named the "infundibular stem", or simply the "infundibulum"). It is from the hypothalamus that hypothalamic tropic factors are released to descend down the pituitary stalk to the pituitary gland where they stimulate the release of pituitary hormones. While the
    9.00
    4 votes
    15
    Olfactory nerve

    Olfactory nerve

    The olfactory nerve, or cranial nerve I, is the first of twelve cranial nerves. It is instrumental in the sense of smell. Derived from the embryonic nasal placode, the olfactory nerve is capable of regeneration. The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity. The olfactory nerves do not form two trunks as do the remaining cranial nerves. Rather, they consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the Cribriform plate of the Ethmoid bone, a sieve-like structure. Olfactory receptor neurons continue to be born throughout life and extend new axons to the olfactory bulb. Olfactory ensheathing glia wrap bundles of these axons and are thought to facilitate their passage into the central nervous system. The sense of smell (olfaction) arises from the stimulation of olfactory (or odorant) receptors by small molecules of different spatial, chemical, and electrical properties that pass over the nasal epithelium in the nasal cavity during inhalation. These interactions are transduced into
    7.60
    5 votes
    16
    Thoracic duct

    Thoracic duct

    In human anatomy, the thoracic duct of the lymphatic system is the largest lymphatic vessel in the body. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal. In adults, the thoracic duct is typically 38-45cm in length and an average diameter of about 5mm. It usually starts from the level of the second lumbar vertebra and extends to the root of the neck. It collects most of the lymph in the body (except that from the right arm and the right side of the chest, neck and head, and lower left lobe of the lung, which is collected by the right lymphatic duct) and drains into the systemic (blood) circulation at the left brachiocephalic vein between the left subclavian and left internal jugular veins. It originates in the abdomen from the confluence of the right and left lumbar trunks and the intestinal trunk, forming a significant pathway upward called the cisterna chyli. It extends vertically in the chest and curves posteriorly to the left carotid artery and left internal jugular vein at the C7 vertebral level to empty into the junction of the left subclavian vein and left jugular vein, below the clavicle, near the shoulders. It traverses
    7.60
    5 votes
    17
    Facial nerve

    Facial nerve

    The facial nerve is the seventh (VII) of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity. It also supplies preganglionic parasympathetic fibers to several head and neck ganglia. The motor part of the facial nerve arises from the facial nerve nucleus in the pons while the sensory part of the facial nerve arises from the nervus intermedius. The motor part and sensory part of the facial nerve enters the petrous temporal bone via the internal auditory meatus (intimately close to the inner ear) then runs a tortuous course (including two tight turns) through the facial canal, emerges from the stylomastoid foramen and passes through the parotid gland, where it divides into five major branches. Though it passes through the parotid gland, it does not innervate the gland (This is the responsibility of cranial nerve IX, the glossopharyngeal nerve). The facial nerve forms the geniculate ganglion prior to entering the facial canal. Distal to stylomastoid foramen, the following nerves branch off
    8.75
    4 votes
    18
    Thoracic cavity

    Thoracic cavity

    The thoracic cavity (or chest cavity) is the chamber of the human body (and other animal bodies) that is protected by the thoracic wall (thoracic cage and associated skin, muscle, and fascia). The thoracic area includes the tendons as well as the cardiovascular system which could be damaged from injury to the back, spine or the neck. Structures within the thoracic cavity include: It contains three potential spaces lined with mesothelium: the paired pleural cavities and the pericardial cavity. The mediastinum comprises those organs which lie in the centre of the chest between the lungs. If the pleural cavity is breached from the outside, as by a bullet wound or knife wound, a pneumothorax, or air in the cavity, may result. If the volume of air is significant, one or both lungs may collapse, which requires immediate medical attention.
    8.75
    4 votes
    19
    Vermiform appendix

    Vermiform appendix

    The appendix (or vermiform appendix; also cecal [or caecal] appendix; also vermix) is a blind-ended tube connected to the cecum, from which it develops embryologically. The cecum is a pouchlike structure of the colon. The appendix is located near the junction of the small intestine and the large intestine. The term "vermiform" comes from Latin and means "worm-shaped". It is widely present in the Euarchontoglires and has also evolved independently in the diprotodont marsupials and is highly diverse in size and shape. The appendix averages 11 cm in length but can range from 2 to 20 cm. The diameter of the appendix is usually between 7 and 8 mm. The longest appendix ever removed measured 26 cm from a patient in Zagreb, Croatia. The appendix is located in the right lower quadrant of the abdomen, near the right hip bone. Its position within the abdomen corresponds to a point on the surface known as McBurney's point (see below). While the base of the appendix is at a fairly constant location, 2 cm below the ileocecal valve, the location of the tip of the appendix can vary from being retrocecal (behind the cecum) (74%) to being in the pelvis to being extraperitoneal. In rare individuals
    8.75
    4 votes
    20
    Cecum

    Cecum

    The cecum or caecum ( /ˈsiːkəm/, plural /ˈsiːkə/; from the Latin caecus meaning blind) is a pouch, usually peritoneal, that is considered to be the beginning of the large intestine. It receives fecal material from the ileum, and connects to the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve (ICV) or Bauhin's valve. It is also separated from the colon by the cecocolic junction. The appendix is connected to the cecum. While the cecum is usually peritoneal, the ascending colon is retroperitoneal. A cecum is present in most amniote species, and also in lungfish, but not in any living species of amphibian. In reptiles, it is usually a single median structure, arising from the dorsal side of the large intestine. Birds typically have two paired ceca, as, unlike other mammals, do hyraxes. Most mammalian herbivores have a relatively large cecum, hosting a large number of bacteria, which aid in the enzymatic breakdown of plant materials such as cellulose; in many species, it is considerably wider than the colon. In contrast, obligatory carnivores, whose diets contain little or no plant material, have a reduced cecum, which is often partially or
    7.40
    5 votes
    21
    White matter

    White matter

    White matter is one of the two components of the central nervous system and consists mostly of glial cells and myelinated axons that transmit signals from one region of the cerebrum to another and between the cerebrum and lower brain centers. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to its usual preservation in formaldehyde. The other main component of the brain is grey matter (actually pinkish tan due to blood capillaries), which is composed of neurons. A third colored component found in the brain that appears darker due to higher levels of melanin in dopaminergic neurons than its nearby areas is the substantia nigra. Note that white matter can sometimes appear darker than grey matter on a microscope slide because of the type of stain used. White matter, long thought to be passive tissue, actively affects how the brain learns and dysfunctions. Whilst grey matter is primarily associated with processing and cognition, white matter modulates the distribution of action potentials, acting as a relay and coordinating communication between
    7.40
    5 votes
    22
    Frenulum labiorum pudendi

    Frenulum labiorum pudendi

    In female human anatomy, the frenulum labiorum pudendi (aka the fourchette or the posterior commissure of the labia minora) is a frenulum where the labia minora meet posteriorly. The fourchette may be torn during delivery due to the sudden stretching of the vulval orifice, or during intercourse. To prevent this tearing in a haphazard manner, obstetricians and, less frequently, midwives may perform an episiotomy, which is a deliberate cut made in the perineum starting from the fourchette and continuing back along the perineum toward the anus. Sometimes this surgical cut may extend to involve the perineal body and thus reduce anal sphicter function. Thus some obstetricians have opted to perform a posterio-lateral cut in the perineum to prevent this potential complication from occurring. The fourchette may also be torn in acts of violence wherein forced entry occurs such as rape. When the fourchette is torn, the bleeding which ensues sometimes requires surgical suturing for containment. "Fourchette" is French for "little fork", and the word is also used as a technical term for a type of dessert fork. (See frenulum for details on the etymology of that word.)
    8.50
    4 votes
    23
    Scapula

    Scapula

    In anatomy, the scapula (Medical Latin), or shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). The scapula forms the posterior (back) located part of the shoulder girdle. In humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage. The costal or ventral surface [Fig. 1] presents a broad concavity, the subscapular fossa. The medial two-thirds of this fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibers of this muscle. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. The dorsal surface [Fig. 2] is arched from above downward,
    9.67
    3 votes
    24
    Biceps brachii muscle

    Biceps brachii muscle

    In human anatomy, the biceps brachii, or simply biceps in common parlance, is, as the name implies, a two-headed muscle. The biceps lie on the upper arm between the shoulder and the elbow. Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm. While the biceps crosses both the shoulder and elbow joints, its main function is at the latter where it flexes the elbow and supinates the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps unscrews the cork (supination), then it pulls the cork out (flexion). The term biceps brachii is a Latin phrase meaning "two-headed [muscle] of the arm", in reference to the fact that the muscle consists of two bundles of muscle, each with its own origin, sharing a common insertion point near the elbow joint. The proper plural form of the Latin adjective biceps is bicipites, a form not in general English use. Instead, biceps is used in both singular and plural (i.e., when referring to both arms). The English form bicep [sic], attested from 1939, is a back formation derived from interpreting the s of biceps as the English plural marker -s. While common even in
    8.25
    4 votes
    25
    Flexor digitorum profundus muscle

    Flexor digitorum profundus muscle

    In human anatomy, the flexor digitorum profundus (FDP, Latin for "deep bender of the fingers") is a muscle in the forearm that flexes the fingers (also known as digits). It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. Together the flexor pollicis longus, pronator quadratus, and flexor digitorum profundus form the deep layer of ventral forearm muscles. Flexor digitorum profundus originates upper 3/4 of anterior & medial surfaces of ulna, interosseous membrane and deep fascia of the forearm. The muscle fans out into four tendons (one to each of the second to fifth fingers) to the palmer base of distal phalanx. Along with flexor digitorum superficialis, it has long tendons that run down the arm and through the carpal tunnel and attach to the palmar side of the phalanges of the fingers. Flexor digitorum profundus lies deep to superficialis, but it attaches more distally. Therefore, profundus's tendons go through the tendons of superficialis, and end up attaching to the distal phalanx. For this reason profundus is also called the perforating muscle. The lumbricals of the hand arise from the radial side of its
    7.00
    5 votes
    26
    Fornix

    Fornix

    The fornix (Latin, "vault" or "arch") is a C-shaped bundle of fibers (axons) in the brain, and carries signals from the hippocampus to the hypothalamus. The fibres begin in the hippocampus on each side of the brain (where they are also known as the fimbria); the separate left and right side are each called the crus of the fornix. The bundles of fibres come together in the midline of the brain, forming the body of the fornix. The inferior edge of the septum pellucidum (a membrane that separates the two lateral ventricles) is attached to the upper face of the fornix body. The body of the fornix travels anteriorly and divides again near the anterior commissure. The left and right parts reseparate, but there is also an anterior/posterior divergence.
    7.00
    5 votes
    27
    Internal carotid artery

    Internal carotid artery

    In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain. Terminologia Anatomica in 1998 subdivided the artery into four parts: "cervical", "petrous", "cavernous", and "cerebral". However, in clinical settings, the classification system of the internal carotid artery follows the 1996 recommendations by Bouthillier, and describes seven anatomical segments of the internal carotid artery. The Bouthillier system is often used clinically by neurosurgeons, neuroradiologists and neurologists. This nomenclature system is a clinical one, based on the angiographic appearance of the artery and its relationship to surrounding anatomy, in contrast to an embryologic classification system. An older clinical classification is based on work by Fischer in 1938 is also commonly used, as well as classification schemes based on the embryologic anatomy of the carotid artery. The segments of the internal carotid artery are as follows: Mnemonic for Branches in Skull: Please Let Children Consume Our Candy The
    7.00
    5 votes
    28
    Levator labii superioris alaeque nasi muscle

    Levator labii superioris alaeque nasi muscle

    The levator labii superioris alaeque nasi muscle is, translated from Latin, the "lifter of both the upper lip and of the wing of the nose". It has the longest name of any muscle in an animal. The muscle is sometimes documented as Otto's muscle as the anatomist was frustrated with the name being so long and tedious to write. The muscle is attached to the upper frontal process of the maxilla and inserts into the skin of the lateral part of the nostril and upper lip. It dilates the nostril and elevates the upper lip, enabling one to snarl. Elvis Presley is famous for his use of this facial expression, earning the muscle this nickname "The Elvis muscle". The long name of muscle can make it hard to remember. A mnemonic to remember its name is, "Little Ladies Snore All Night." Snore- because it is the labial elevator closest to the nose.
    8.00
    4 votes
    29
    Lunate bone

    Lunate bone

    The lunate bone (semilunar bone) is a carpal bone (wrist bone) in the human hand that may be distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row of the carpus (wrist) region between the fore arm and hand (manus). In standard medical posture, the lunate carpal bone is situated between the lateral Scaphoid bone and medial Triquetral bone. The lunate carpal bone straddles distally the bordering ulna and radius bones and proximally to distal carpus (wrist) Trapezium bone and Trapezoid bone. The etymology of the Lunate bone derives from the Latin luna which means "moon", the lunate bone looks semi-similar to a crescent moon. In amphibians and reptiles, the bone is instead referred to as the intermedium, because of its position between the other two proximal carpals. The superior surface, convex and smooth, articulates with the radius. The inferior surface is deeply concave, and of greater extent from before backward than transversely: it articulates with the head of the capitate, and, by a long, narrow facet (separated by a ridge from the general surface), with the hamate. The dorsal and palmar surfaces are rough, for the
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    Mammillary body

    Mammillary body

    The mammillary bodies (mamillary bodies) are a pair of small round bodies, located on the undersurface of the brain, that, as part of the diencephalon form part of the limbic system. They are located at the ends of the anterior arches of the fornix. They consist of two groups of nuclei, the medial mammillary nuclei and the lateral mammillary nuclei. Neuroanatomists have often categorized the mammillary bodies as part of the hypothalamus. They are connected to other parts of the brain (as shown in the schematic, below left), and act as a relay for impulses coming from the amygdalae and hippocampi, via the mamillo-thalamic tract to the thalamus. This circuit, from amygdalae to mammillary bodies, and then on to the thalamus, is part of the larger 'Papez circuit'. They, along with the anterior and dorsomedial nuclei in the thalamus, are involved with the processing of recognition memory. They are believed to add the element of smell to memories. Damage to the mammillary bodies due to thiamine deficiency is implied in pathogenesis of Wernicke-Korsakoff syndrome. Symptoms include impaired memory, also called anterograde amnesia, suggesting that the mammillary bodies may be important for
    8.00
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    31
    Stomach

    Stomach

    The stomach is a muscular, hollow, dilated part of the digestion system which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects (mid-gut), and molluscs. It is involved in the second phase of digestion, following mastication (chewing). The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines. The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos, ultimately from stoma (στόμα), "mouth". The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster (γαστήρ). Bolus (masticated food) enters the stomach through the oesophagus via the oesophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin) and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of two for the proteases to work. Food is churned by the stomach
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    Neurolemma

    Neurolemma

    Neurolemma (also known as neurilemma or sheath of Schwann) is the outermost nucleated cytoplasmic layer of Schwann cells that surrounds the axon of the neuron. It forms the outermost layer of the nerve fiber in the peripheral nervous system. The neurolemma is underlain by the basal lamina (referred to as the medullary sheath in the included illustrations). In CNS, axons are myelinated by oligodendrocytes, thus lack neurolemma. The myelin sheaths of Oligodendrocytes do not have neurolemma because excess cytoplasm is directed centrally toward the Oligodendrocyte cell body. A neurilemoma is a tumor of the neurilemma.
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    33
    Turbinate

    Turbinate

    In anatomy, a nasal concha (or turbinate) is a long, narrow and curled bone shelf (shaped like an elongated sea-shell) that protrudes into the breathing passage of the nose. Turbinate bone refers to any of the scrolled spongy bones of the nasal passages in vertebrates. In humans, the turbinates divide the nasal airway into four groove-like air passages, and are responsible for forcing inhaled air to flow in a steady, regular pattern around the largest possible surface of cilia and climate-controlling tissue. A rapidly dilating arteriolar circulation to these bones may lead to a sharp increase in the pressure within in response to acute cooling of the body core - the pain from this pressure is often referred to as "brain freeze", and is frequently associated with the rapid consumption of ice cream. Turbinates are composed of pseudostratified columnar, ciliated respiratory epithelium with a thick, vascular, and erectile glandular tissue layer. The turbinates are located laterally in the nasal cavities, curling medially and downward into the nasal airway. Each pair is composed of one turbinate in either side of the nasal cavity, divided by the septum. The inferior turbinates are the
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    Axon

    Axon

    An axon (also known as a nerve fiber) is a long, slender projection of a nerve cell, or neuron, that typically conducts electrical impulses away from the neuron's cell body. In certain sensory neurons (pseudounipolar neurons), such as those for touch and warmth, the electrical impulse travels along an axon from the periphery to the cell body, and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction causes many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. An axon is one of two types of protoplasmic protrusions that extrude from the cell body of a neuron, the other type being dendrites. Axons are distinguished from dendrites by several features, including shape (dendrites often taper while axons usually maintain a constant radius), length (dendrites are restricted to a small region around the cell body while axons can be much longer), and function (dendrites usually receive signals while axons usually transmit them). All of these rules have exceptions, however. Some types of neurons have no axon and transmit signals from their dendrites. No neuron ever has more than one axon; however
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    Central sulcus

    Central sulcus

    The central sulcus is a fold in the cerebral cortex of brains in vertebrates. Also called the central fissure, it was originally called the fissure of Rolando or the Rolandic fissure, after Luigi Rolando. The central sulcus is a prominent landmark of the brain, separating the parietal lobe from the frontal lobe and the primary motor cortex from the primary somatosensory cortex. List of human anatomical parts named after people
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    36
    Accessory nerve

    Accessory nerve

    In anatomy, the accessory nerve is a nerve that controls specific muscles of the shoulder and neck. As part of it was formerly believed to originate in the brain, it is considered a cranial nerve. Based on its location relative to other such nerves, it is designated the eleventh of twelve cranial nerves, and is thus abbreviated CN XI. Traditional descriptions of the accessory nerve divide it into two parts: a spinal part and a cranial part. But because the cranial component rapidly joins the vagus nerve and serves the same function as other vagal nerve fibers, modern descriptions often consider the cranial component part of the vagus nerve and not part of the accessory nerve proper. Thus in contemporary discussions of the accessory nerve, the common practice is to dismiss the cranial part altogether, referring to the accessory nerve specifically as the spinal accessory nerve. The spinal accessory nerve provides motor innervation from the central nervous system to two muscles of the neck: the sternocleidomastoid muscle and the trapezius muscle. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle has several actions on the scapula, including shoulder
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    37
    Axillary nerve

    Axillary nerve

    The axillary nerve or the circumflex nerve is a nerve of the human body, that comes off the of the brachial plexus (upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein. The axillary nerve supplies three muscles; deltoid (a muscle of the shoulder), teres minor (one of the rotator cuff muscles) and the long head of the triceps brachii (an elbow extensor). The axillary nerve also carries sensory information from the shoulder joint, as well as the skin covering the inferior region of the deltoid muscle - the "regimental badge" area (which is innervated by the Superior Lateral Cutaneous Nerve branch of the Axillary nerve). The posterior cord splits inferiorly to the glenohumeral joint giving rise to the axillary nerve which wraps around the anatomical neck of the humerus, and the radial nerve which wraps around the humerus anteriorly and descends along its lateral border. It lies at first behind the axillary artery, and in front of the subscapularis, and passes downward to the lower border of that
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    Dentate gyrus

    Dentate gyrus

    The dentate gyrus is part of the hippocampal formation. It is thought to contribute to the formation of new memories, as well as possessing other functional roles. It is notable as being one of a select few brain structures currently known to have high rates of neurogenesis in adult rats (other sites include the olfactory bulb and cerebellum). The dentate gyrus cells receive excitatory input from the entorhinal cortex, in the medial temporal lobe, through the perforant path into the molecular layer. This activates pyramidal cells among the CA4 and CA3 pyramidal neurons (CA stands for cornu ammonis), which are components of Ammon's horn within the hippocampus. Tracts exit CA3 neurons via the Schaffer collaterals and activate CA1 pyramidal cells, allowing the dentate gyrus to be in a position to control the flow of information within the hippocampus. The dentate gyrus consists of three layers of neurons: molecular, granular, and polymorphic. The middle layer is most prominent and contains granule cells that project to the CA3 subfield of the hippocampus. These granule cells project mostly to interneurons, but also to pyramidal cells and are the principal excitatory neurons of the
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    39
    Temporal bone

    Temporal bone

    The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum. The temporal bone supports that part of the face known as the temple. The temporal bone consists of four parts: The structure of the squama is like that of the other cranial bones: the mastoid portion is spongy, and the petrous portion dense and hard. In evolutionary terms, the temporal bone is derived from the fusion of many bones that are often separate in non-human mammals: This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    40
    Aorta

    Aorta

    The aorta ( /eɪˈɔrtə/; from Greek ἀορτή - aortē, from ἀείρω - aeirō "I lift, raise") is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it bifurcates into two smaller arteries (the common iliacs). The aorta distributes oxygenated blood to all parts of the body through the systemic circulation. The aorta is usually divided into five segments/sections: All amniotes have a broadly similar arrangement to that of humans, albeit with a number of individual variations. In fish, however, there are two separate vessels referred to as aortas. The ventral aorta carries de-oxygenated blood from the heart to the gills; part of this vessel forms the ascending aorta in tetrapods (the remainder forms the pulmonary artery). A second, dorsal aorta carries oxygenated blood from the gills to the rest of the body, and is homologous with the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills. Amphibians also retain the fifth connecting vessel, so that the aorta has two parallel arches. In mammalian and avian embryological development, the pharyngeal arch
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    41
    Cornea

    Cornea

    The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. While the cornea contributes most of the eye's focusing power, its focus is fixed. The curvature of the lens, on the other hand, can be adjusted to "tune" the focus depending upon the object's distance. Medical terms related to the cornea often start with the prefix "kerat-" from the Greek word κέρας, horn. The cornea has unmyelinated nerve endings sensitive to touch, temperature and chemicals; a touch of the cornea causes an involuntary reflex to close the eyelid. Because transparency is of prime importance the cornea does not have blood vessels; it receives nutrients via diffusion from the tear fluid through the outside surface and the aqueous humour through the inside surface, and also from neurotrophins supplied by nerve fibres that innervate it. In humans, the cornea has a diameter of about 11.5 mm and a thickness of 0.5–0.6 mm in the center and
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    42
    Bulbourethral gland

    Bulbourethral gland

    A bulbourethral gland, also called a Cowper's gland for anatomist William Cowper, is one of two small exocrine glands present in the reproductive system of human males. They are homologous to Bartholin's glands in females. Bulbourethral glands are located posterior and lateral to the membranous portion of the urethra at the base of the penis, between the two layers of the fascia of the urogenital diaphragm, in the deep perineal pouch. They are enclosed by transverse fibers of the sphincter urethrae membranaceae muscle. The bulbourethral glands are compound tubulo-alveolar glands, each approximately the size of a pea. They are composed of several lobules held together by a fibrous covering. Each lobule consists of a number of acini, lined by columnar epithelial cells, opening into a duct that joins with the ducts of other lobules to form a single excretory duct. This duct is approximately 2.5 cm long and opens into the urethra at the base of the penis. The glands gradually diminish in size with advancing age. During sexual arousal each gland produces a clear, salty, viscous secretion known as pre-ejaculate. This fluid helps to lubricate the urethra for spermatozoa to pass through,
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    43
    Dendrite

    Dendrite

    Dendrites (from Greek δένδρον déndron, "tree") are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. Electrical stimulation is transmitted onto dendrites by upstream neurons via synapses which are located at various points throughout the dendritic arbor. Dendrites play a critical role in integrating these synaptic inputs and in determining the extent to which action potentials are produced by the neuron. Recent research has also found that dendrites can support action potentials and release neurotransmitters, a property that was originally believed to be specific to axons. The long outgrowths on immune system dendritic cells are also called dendrites. These dendrites do not process electrical signals. Certain classes of dendrites (i.e. Purkinje cells of cerebellum, cerebral cortex) contain small projections referred to as "appendages" or "spines". Appendages increase receptive properties of dendrites to isolate signal specificity. Increased neural activity at spines increases their size and conduction which is thought to play a role in
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    Nasal bone

    Nasal bone

    The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose. Each has two surfaces and four borders. The outer surface is concavoconvex from above downward, convex from side to side; it is covered by the Procerus and Compressor naris, and perforated about its center by a foramen, for the transmission of a small vein. The inner surface is concave from side to side, and is traversed from above downward, by a groove for the passage of a branch of the nasociliary nerve. The nasal articulates with four bones: two of the cranium, the frontal and ethmoid, and two of the face, the opposite nasal and the maxilla. In primitive bony fish and tetrapods, the nasal bones are the most anterior of a set of four paired bones forming the roof of the skull, being followed in sequence by the frontals, the parietals, and the postparietals. Their form in living species is highly variable, depending on the shape of the head, but they generally form the roof of the snout or beak, running from the nostrils to a position short of the orbits. In most
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    Occipital lobe

    Occipital lobe

    The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1 (visual one). Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the posterior pole of the occipital lobe. V1 is often also called striate cortex because it can be identified by a large stripe of myelin, the Stria of Gennari. Visually driven regions outside V1 are called extrastriate cortex. There are many extrastriate regions, and these are specialized for different visual tasks, such as visuospatial processing, color discrimination and motion perception. The name derives from the overlying occipital bone, which is named from the Latin oc- + caput, "back of the head". The two occipital lobes are the smallest of four paired lobes in the human cerebral cortex. Located in the rearmost portion of the skull, the occipital lobes are part of the forebrain. The cortical lobes are not defined by any internal structural features, but rather by the bones of the skull that overlie them. Thus, the occipital lobe
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    Coronary circulation

    Coronary circulation

    Coronary circulation is the circulation of blood in the blood vessels of the heart muscle (myocardium). The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries. The vessels that remove the deoxygenated blood from the heart muscle are known as cardiac veins. These include the great cardiac vein, the middle cardiac vein, the small cardiac vein and the anterior cardiac veins. The coronary arteries that run on the surface of the heart are called epicardial coronary arteries. These arteries, when healthy, are capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle. These relatively narrow vessels are commonly affected by atherosclerosis and can become blocked, causing angina or a heart attack. (See also: circulatory system.) The coronary arteries that run deep within the myocardium are referred to as subendocardial. The coronary arteries are classified as "end circulation", since they represent the only source of blood supply to the myocardium: there is very little redundant blood supply, which is why blockage of these vessels can be so critical. Both of these arteries originate from the left
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    Fibrocartilage

    Fibrocartilage

    White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its flexibility and toughness to the former of these constituents, and its elasticity to the latter. It is the only type of cartilage that contains type I collagen in addition to the normal type II. Fibrocartilage is found in the pubic symphysis, the annulus fibrosus of intervertebral discs, meniscus, and the TMJ. During labor, relaxin loosens the pubic symphysis to aid in delivery, but this can lead to later joint problems. If hyaline cartilage is torn all the way down to the bone, the blood supply from inside the bone is sometimes enough to start some healing inside the lesion. In cases like this, the body will form a scar in the area using a special type of cartilage called fibrocartilage. Fibrocartilage is a tough, dense, fibrous material that helps fill in the torn part of the cartilage. Yet it's not an ideal replacement for the smooth, glassy articular cartilage that normally covers the surface of the knee joint. Degeneration of fibrocartilage is seen in degenerative disc disease. This article was originally based on an entry from a public domain edition
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    Incisor

    Incisor

    Incisors (from Latin incidere, "to cut") are the first four front teeth present in heterodont mammals. They are located in the premaxilla above and on the mandible below. In many omnivorous mammals, such as the human, they are adapted for shearing sharply. In cats, the incisors are small; biting off meat is done with the canines and the carnassials. In elephants, the upper incisors are modified into curved tusks, just as is the case with Narwhals, where normally one of them develops into a straight and twisted tusk. The incisors of rodents grow throughout life and are worn by gnawing. Adult humans normally have eight incisors, two of each type. The types of incisor are: Children with a full set of deciduous teeth (primary teeth) also have eight incisors, named the same way as in permanent teeth. Young children may have from zero to eight incisors depending on the stage of their tooth eruption and tooth development. Among other animals, some other primates, cats and horses have twelve. Rodents have four, while Foxes have nine. Rabbits and hares (lagomorphs) were once considered rodents, but are distinguished by having eight—one small pair, called "peg teeth", is located directly
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    Motor nerve

    Motor nerve

    Motor nerves allow the brain to stimulate muscle contraction. A motor nerve is an efferent nerve that exclusively contains the axons of somatic and branchial motoneurons, which innervate skeletal muscles (that ensure locomotion) and branchial muscles (that motorize the face and neck).
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    50
    Olfactory bulb

    Olfactory bulb

    The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors. In most vertebrates, the olfactory bulb is the most rostral (forward) part of the brain. In humans, however, the olfactory bulb is on the inferior (bottom) side of the brain. The olfactory bulb is supported and protected by the cribriform plate of the ethmoid bone, which in mammals separates it from the olfactory epithelium, and which is perforated by olfactory nerve axons. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb. The main olfactory bulb has a multi-layered cellular architecture. In order from surface to the center the layers are The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell. As a neural circuit, the glomerular layer receives direct input from olfactory nerves, made up of the axons from approximately ten million olfactory receptor neurons in the olfactory mucosa, a region of the nasal cavity. The ends of the axons cluster in spherical structures known as glomeruli such that each glomerulus receives input primarily from olfactory
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    51
    Ossicles

    Ossicles

    The ossicles (also called auditory ossicles) are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. The term "ossicles" literally means "tiny bones" and commonly refers to the auditory ossicles, though the term may refer to any small bone throughout the body. Ossicle dates to c. 1570, from Latin Ossiculum, a diminutive of Latin Os "bone" (Genitive: Ossis). The malleus gets its name from Latin malleus, meaning "hammer", the Incus gets its name from Latin Incus meaning "anvil" from incudere meaning "to forge with a hammer", and the Stapes gets its name from Modern Latin "stirrup," probably an alteration of Late Latin Stapia related to stare "to stand" and pedem, an accusative of pes "foot", so called because the bone is shaped like a stirrup - this was an invented Modern Latin word for "stirrup," for which there was no classical Latin word, as the ancients did not use stirrups. The ossicles are, in order from the eardrum to the inner ear (from superficial to deep): the
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    52
    Sacrum

    Sacrum

    In humans, the sacrum (plural: sacrums or sacra) is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx (tailbone). It consists of usually five initially unfused vertebrae which begin to fuse between ages 16–18 and are usually completely fused into a single bone by age 34. It is curved upon itself and placed obliquely (that is, tilted forward). It is kyphotic — that is, concave facing forwards. The base projects forward as the sacral promontory internally, and articulates with the last lumbar vertebra to form the prominent sacrovertebral angle. The central part is curved outward towards the posterior, allowing greater room for the pelvic cavity. The two lateral projections of the sacrum are called ala (wings), and articulate with the ilium at the L-shaped sacroiliac joints. The name is derived from the Latin (os) sacrum, (sacer, sacra, sacrum, "sacred"), a translation of the Greek hieron (osteon), meaning sacred or strong bone. Since the sacrum is the seat of the organs of procreation,
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    53
    Epiphysis

    Epiphysis

    The epiphysis (/ɛˈpɪfəsəs/) is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the joint, the epiphysis is covered with articular cartilage; below that covering is a zone similar to the epiphyseal plate, known as subchondral bone (see Wiktionary:subchondral). The epiphysis is filled with red bone marrow, which produces erythrocytes (red blood cells). There are four types of epiphysis: Pathologies of the epiphysis include avascular necrosis and osteochondritis dissecans (OCD). OCD involves the subchondral bone. Epiphyseal lesions include chondroblastoma and giant-cell tumor.
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    Hyoid bone

    Hyoid bone

    The hyoid bone (lingual bone) (/ˈhaɪɔɪd/; Latin os hyoideum) is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies at the level of the base of the mandible in the front and the third cervical vertebra behind. Unlike other bones, the hyoid is only distantly articulated to other bones by muscles or ligaments. The hyoid is anchored by muscles from the anterior, posterior and inferior directions, and aids in tongue movement and swallowing. The hyoid bone provides attachment to the muscles of the floor of the mouth and the tongue above, the larynx below, and the epiglottis and pharynx behind. Its name is derived from the Greek word hyoeides meaning "shaped like the letter upsilon" (υ). The bone consists of a central part, called the body and two pairs of cornua, the greater cornu and the lesser cornu. The second pharyngeal arch gives rise to the lesser cornu of hyoid and the superior part of body of hyoid. The cartilage of the third pharyngeal arch forms the greater cornu of hyoid and the lower portion of the body of hyoid. The hyoid is ossified from six centers: two for the body, and one for each cornu.
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    55
    Optic nerve

    Optic nerve

    The optic nerve, also known as cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve does not regenerate after transection. The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system, as it is derived from an outpouching of the diencephalon during embryonic development. As a consequence, the fibres are covered with myelin produced by oligodendrocytes, rather than Schwann cells, which are found in the peripheral nervous system, and are encased within the meninges. Peripheral neuropathies like Guillain-Barré syndrome do not affect the optic nerve. The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Fibre tracks of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration, and, hence, optic nerve damage produces irreversible blindness. The fibres from the retina run along the optic nerve to nine primary visual nuclei
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    56
    Salivary gland

    Salivary gland

    The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose. In other organisms such as insects, salivary glands are often used to produce biologically important proteins like silk or glues, and fly salivary glands contain polytene chromosomes that have been useful in genetic research. The gland is internally divided into lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out into the lobules. In the duct system, the lumina are formed by intercalated ducts, which in turn join to form striated ducts. These drain into ducts situated between the lobes of the gland (called interlobar ducts or secretory ducts). All of the human salivary glands terminate in the mouth, where the saliva proceeds to aid in digestion. The saliva that salivary glands release is quickly inactivated in the stomach by the acid that is present there but the saliva also contains enzymes that are actually activated by the acid. The parotid gland is a salivary gland wrapped around the mandibular ramus in humans. It is one of a pair being the largest of the salivary glands, it
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    57
    Semicircular canal

    Semicircular canal

    A semicircular canal is one of three semicircular, interconnected tubes located inside each ear. The three canals are: The semicircular ducts provide sensory input for experiences of rotary movements. They are oriented along the pitch, roll, and yaw axes. The anterior and posterior semicircular ducts are oriented vertically at right angles to each other. The lateral semicircular duct is about 30-degree angle from the horizontal plane. The orientations of the ducts cause a different duct to be stimulated by rotation of the head in different planes. Thus, the horizontal canal detects horizontal head movements (such as when you spin in a rotating chair), while the superior and posterior canals detect vertical head movements (such as when you bend forward to pick something up from the floor). The semicircular canals are a component of the bony labyrinth. Among species of mammals, the size of the semicircular canals is correlated with their type of locomotion. Specifically, species that are agile and have fast, jerky locomotion have larger canals relative to their body size than those that move more cautiously. Each canal is filled with a fluid called endolymph and contains motion
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    58
    Seminal vesicle

    Seminal vesicle

    The seminal vesicles (glandulae vesiculosae) or vesicular glands are a pair of simple tubular glands posteroinferior to the urinary bladder of male mammals. It is located within the pelvis. Each seminal gland spreads approximately 5 cm, though the full length of seminal vesicle is approximately 10 cm, but it is curled up inside of the gland's structure. Each gland forms as an outpocketing of the wall of ampulla of each vas deferens. The excretory duct of seminal gland opens into the vas deferens as it enters the prostate gland. The seminal vesicles secrete a significant proportion of the fluid that ultimately becomes semen. Lipofuscin granules from dead epithelial cells give the secretion its yellowish color. About 50-70% of the seminal fluid in humans originates from the seminal vesicles, but is not expelled in the first ejaculate fractions which are dominated by spermatozoa and zinc-rich prostatic fluid. The excretory duct of each seminal gland opens into the corresponding vas deferens as it enters the prostate gland. Seminal vesicle fluid is alkaline, resulting in human semen having a mildly alkaline pH. The alkalinity of semen helps neutralize the acidity of the vaginal tract,
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    59
    Spermatozoon

    Spermatozoon

    A spermatozoon (alternate spelling spermatozoön; plural spermatozoa; from Ancient Greek: σπέρμα "seed" and Ancient Greek: ζῷον "living being") is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, that normally develops into an embryo.) Sperm cells contribute approximately half of the nuclear genetic information to the diploid offspring (excluding, in most cases, mitochondrial DNA). In mammals, the sex of the offspring is determined by the sperm cell: a spermatozoon bearing a Y chromosome will lead to a male (XY) offspring, while one bearing an X chromosome will lead to a female (XX) offspring—the X chromosome. Sperm cells were first observed by Anton van Leeuwenhoek in 1677. The human sperm cell is the reproductive cell in males and will only survive in warm environments; once it leaves the male body the sperm's survival likelihood is reduced and it may die, thereby decreasing the total sperm quality. Sperm cells come in two types, "female" and "male". Sperm cells that give rise to female (XX) offspring after fertilization differ in that they
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    60
    Thenar eminence

    Thenar eminence

    The thenar eminence (from the Greek "θέναρ" - thenar, "palm of the hand" and the Latin word "eminentia", meaning projection,) refers to the group of muscles on the palm of the human hand at the base of the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex. The following three muscles are considered part of the thenar eminence: Another muscle that controls movement of the thumb is adductor pollicis. It lies deeper and more distal to flexor pollicis brevis. Despite its name, its main action is mainly rotation and opposition. It is not in the thenar group of muscles, so is supplied by the ulnar nerve. The Opponens pollicis and Abductor pollicis brevis are normally innervated by the median nerve. The Flexor pollicis brevis can be innervated by the median or ulnar nerve. The adductor pollicis is typically innervated by the ulnar nerve. There are normal variations. In a Cannieu-Riche anastomasis, fibers from the deep palmar branch of the ulnar nerve innervate the opponens pollicis and/or abductor pollicis brevis. Regardless of their final innervation, the nerves that reach the thenar muscles arise from the C8 and T1 roots, pass
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    61
    Trochlear nerve

    Trochlear nerve

    The trochlear nerve (the fourth cranial nerve, also called the fourth nerve, IV) is a motor nerve (a “somatic efferent” nerve) that innervates a single muscle: the superior oblique muscle of the eye. The trochlear nerve is unique among the cranial nerves in several respects. It is the smallest nerve in terms of the number of axons it contains. It has the greatest intracranial length. Other than the optic nerve (cranial nerve II), it is the only cranial nerve that decussates (crosses to the other side) before innervating its target. Finally, it is the only cranial nerve that exits from the dorsal aspect of the brainstem. Homologous trochlear nerves are found in all jawed vertebrates. The unique features of the trochlear nerve, including its dorsal exit from the brainstem and its contralateral innervation, are seen in the primitive brains of sharks. The human trochlear nerve is derived from the basal plate of the embryonic midbrain. The trochlear nerve emerges from the dorsal aspect of the brainstem at the level of the caudal mesencephalon, just below the inferior colliculus. It circles anteriorly around the brainstem and runs forward toward the eye in the subarachnoid space. It
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    62
    Supraorbital nerve

    Supraorbital nerve

    The supraorbital nerve is a terminal branch of the frontal nerve. It passes through the supraorbital foramen, and gives off, in this situation, palpebral filaments to the upper eyelid. Additionally it supplies the conjunctiva of the eye, the frontal sinus and the skin from the forehead extending back to the middle of the scalp. It then ascends upon the forehead, and ends in two branches, a medial and a lateral, which supply the integument of the scalp, reaching nearly as far back as the lambdoidal suture; they are at first situated beneath the Frontalis: Both branches supply small twigs to the pericranium. This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    63
    Vomer

    Vomer

    The vomer (/ˈvoʊmər/) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomeronasal organ, also called Jacobson's organ, is a chemoreceptor organ named for its closeness to the vomer and nasal bones, and is particularly developed in animals such as cats (who adopt a characteristic pose called the Flehmen reaction or flehming when making use of it), and is thought to have to do with the perception of certain pheromones. It has been suggested that by alternately thrusting with the tongue against the roof of the mouth while pressing with the fingers between the eyebrows, one can move the vomer, and if repeated for about 20 seconds, the sinuses will discharge, thus rapidly clearing a stuffy head without the use of drugs. The vomer is situated in the median plane, but its anterior portion is frequently bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal septum; it has two surfaces and four borders. The surfaces are marked by small furrows for blood
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    64
    Uterus

    Uterus

    The uterus (from Latin "uterus", plural uteri) or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species. It is within the uterus that the fetus develops during gestation, usually developing completely in placental mammals such as humans and partially in marsupials such as kangaroos and opossums. Two uteri usually form initially in a female fetus, and in placental mammals they may partially or completely fuse into a single uterus depending on the species. In many species with two uteri, only one is functional. Humans and other higher primates such as chimpanzees, along with horses, usually have a single completely fused uterus, although in some individuals the uteri may not have completely fused. In English, the term uterus is used consistently within the medical and related professions, while the Germanic-derived term womb is more common in everyday usage. Most animals that lay eggs, such as birds and reptiles, including most ovoviviparous species, have an oviduct instead of a uterus. Note however, that recent
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    65
    Sternum

    Sternum

    The sternum or breastbone, in vertebrate anatomy, is a flat bone that lies in in the middle front part of the rib cage. It is endochondral in origin . It probably first evolved in early tetrapods as an extension of the pectoral girdle; it is not found in fish. In amphibians and reptiles it is typically a shield-shaped structure, often composed entirely of cartilage. It is absent in both turtles and snakes. In birds it is a relatively large bone and typically bears an enormous projecting keel to which the flight muscles are attached. Only in mammals does the sternum take on the elongated, segmented form seen in humans. In some mammals, such as opossums, the individual segments never fuse and remain separated by cartilagenous plates throughout life.
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    66
    Caudate nucleus

    Caudate nucleus

    The caudate nucleus is a nucleus located within the basal ganglia of the brains of many animal species. The caudate nucleus is an important part of the brain's learning and memory system. The caudate nuclei are located near the center of the brain, sitting astride the thalamus. There is a caudate nucleus within each hemisphere of the brain. Individually, they resemble a C-shape structure with a wider "head" (caput in Latin) at the front, tapering to a "body" (corpus) and a "tail" (cauda). Sometimes a part of the caudate nucleus is referred to as the "knee" (genu). The head and body of the caudate nucleus form part of the floor of the anterior horn of the lateral ventricle. After the body travels briefly towards the back of the head, the tail curves back toward the anterior, forming the roof of the inferior horn of the lateral ventricle. This means that a coronal (on a plane parallel to the face) section that cuts through the tail will also cross the body and head of the caudate nucleus. The caudate nucleus is related anatomically to a number of other structures. It is separated from the lenticular nucleus (made up of the globus pallidus and the putamen) by the anterior limb of the
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    67
    Inner ear

    Inner ear

    The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts: The inner ear is found in all vertebrates, with substantial variations in form and function. The inner ear is innervated by the eighth cranial nerve in all vertebrates. The human inner ear develops during week 4 of embryonic development from the auditory placode, a thickening of the ectoderm which gives rise to the bipolar neurons of the cochlear and vestibular ganglions. As the auditory placode invaginates towards the embryonic mesoderm, it forms the auditory vesicle or otocysts. The auditory vesicle will give rise to the utricluar and saccular components of the membranous labyrinth. They contain the sensory hair cells and otoliths of the macula of utricle and of the saccule, respectively, which respond to linear acceleration and the force of gravity. The utricular division of the auditory vesicle also responds to angular acceleration, as well as the endolymphatic sac and duct that connect the saccule and utricle. Beginning in the fifth week of development, the
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    68
    Patella

    Patella

    The patella, also known as the knee cap or kneepan, is a thick, circular-triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint. It is the largest sesamoid bone in the human body. The patella is roughly triangular in shape with its base facing proximally (towards the torso) and its tip (apex patellae) facing distally (towards the feet). Its anterior and posterior surfaces are joined laterally (left/right) by a thinner margin and medially (towards centre) by a thicker margin. The anterior surface can be divided into three parts: The posterior surface is divided into two parts. The upper three-quarters articulates with the femur and is subdivided into a medial and a lateral facet by a vertical ledge which varies in shape. Four main types of articular surface can be distinguished: In the adult the articular surface is about 12 cm (1.9 sq in) and covered by cartilage, which can reach a maximal thickness of 6 mm (0.24 in) in the centre at about 30 years of age. The lower part of the posterior surface has vascular canaliculi filled and is filled by fatty tissue, the infrapatellar fat pad. Emarginations (i.e. patella
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    69
    Trapezoid bone

    Trapezoid bone

    The trapezoid bone (lesser multangular bone) is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the palmar surface; and by its having four articular facets touching each other, and separated by sharp edges. It is homologous with the "second distal carpal" of reptiles and amphibians. The etymology derives from the Greek trapezion which means "irregular quadrilateral," from tra- "four" and peza "foot" or "edge." Literally, "a little table" from trapeza meaning "table" and -oeides "shaped." The superior surface, quadrilateral, smooth, and slightly concave, articulates with the scaphoid. The inferior surface articulates with the proximal end of the second metacarpal bone; it is convex from side to side, concave from before backward and subdivided by an elevated ridge into two unequal facets. The dorsal and palmar surfaces are rough for the attachment of ligaments, the former being the larger of the two. The lateral surface, convex and smooth, articulates with the trapezium. The medial surface is concave and smooth in front, for
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    70
    Extensor carpi radialis brevis muscle

    Extensor carpi radialis brevis muscle

    The Extensor carpi radialis brevis is shorter and thicker than the extensor carpi radialis longus. The longus muscle can be found above the distal end of the Extensor carpi radialis brevis. It arises from the lateral epicondyle of the humerus, by the common extensor tendon; from the radial collateral ligament of the elbow-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles. The fibres end approximately at the middle of the forearm in the form of a flat tendon, which is closely connected with that of the extensor carpi radialis longus, and accompanies it to the wrist; it passes beneath the Abductor pollicis longus and Extensor pollicis brevis, beneath the extensor retinaculum, beneath the dorsal carpal ligament, and inserts into the lateral dorsal surface of the base of the third metacarpal bone, with a few fibres inserting into the medial dorsal surface of the second metacarpal bone. Under the dorsal carpal ligament the tendon lies on the back of the radius in a shallow groove called Lister's tubercle, to the ulnar side of that which lodges the tendon of the Extensor carpi radialis longus, and separated
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    71
    Oval window

    Oval window

    The oval window (or vestibular window) is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear. Vibrations that come into contact with the tympanic membrane travel through the three ossicles and into the inner ear. The oval window is the intersection of the middle ear with the inner ear, and is directly contacted by the stapes; by the time vibrations reach the oval window, they have been amplified over twenty times from what they were when they contacted the tympanic membrane, a testament to the amplifying power of the middle ear. It is a reniform (kidney-shaped) opening leading from the tympanic cavity into the vestibule of the internal ear; its long diameter is horizontal, and its convex border is upward. In the recent state it is occupied by the base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen. This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    72
    Purkinje fibers

    Purkinje fibers

    For the nervous cells, see Purkinje cell 'Purkinje fibers' (Purkyne tissue or Subendocardial branches) are located in the inner ventricular walls of the heart, just beneath the endocardium. These fibers are specialized myocardial fibers that conduct an electrical stimulus or impulse that enables the heart to contract in a coordinated fashion. Purkinje fibers are a unique end-organ cardiac extension of the Autonomic Nervous System. Further histologic examination reveals that these fibers are split into left and right trees as well as atrial and ventricular contributions. The electrical origin of atrial Purkinje fibers arrives from the Sinoatrial Node. The following electrical origin of the ventricular Purkinje fibers arrives from the Atrioventricular Node. Given no aberrant channels, the atrial and ventricular Purkinje trees are distinctly shielded from each other by collagen or the cardiac skeleton. The Purkinje fibers are uniquely dedicated to sympathetic electrical depolarization of the right and left atria and ventricles. The Purkinje fibers are further specialized to rapidly conduct impulses (numerous sodium ion channels and mitochondria, fewer myofibrils than the surrounding
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    73
    Lamina propria

    Lamina propria

    The lamina propria is a constituent of the moist linings known as mucous membranes or mucosa, which line various tubes in the body (such as the respiratory tract, the gastrointestinal tract, and the urogenital tract). The lamina propria (more correctly lamina propria mucosæ) is a thin layer of loose connective tissue which lies beneath the epithelium and together with the epithelium constitutes the mucosa. As its Latin name indicates it is a characteristic component of the mucosa, "the mucosa's own special layer". Thus the term mucosa or mucous membrane always refers to the combination of the epithelium plus the lamina propria. The lamina propria contains capillaries and a central lacteal (lymph vessel) in the small intestine, as well as lymphoid tissue. Lamina propria also contains glands with the ducts opening on to the mucosal epithelium, that secrete mucus and serous secretions. The lamina propria is also rich in immune cells known as lymphocytes. A majority of these cells are IgA-secreting B cells.
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    74
    Mucous membrane

    Mucous membrane

    The mucous membranes (or mucosae; singular mucosa) are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs. They are at several places contiguous with skin: at the nostrils, the mouth, the lips, the eyelids, the ears, the genital area, and the anus. The sticky, thick fluid secreted by the mucous membranes and glands is termed mucus. The term mucous membrane refers to where they are found in the body and not every mucous membrane secretes mucus. The glans clitoridis, glans penis (head of the penis), along with the inside of the foreskin and the clitoral hood, are mucous membranes. The urethra is also a mucous membrane. The secreted mucus traps the pathogens in the body, preventing any further activities of diseases.
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    75
    Sartorius muscle

    Sartorius muscle

    The Sartorius muscle – the longest muscle in the human body – is a long thin muscle that runs down the length of the thigh. Its upper portion forms the lateral border of the femoral triangle. The sartorius muscle arises by tendinous fibres from the anterior superior iliac spine, running obliquely across the upper and anterior part of the thigh in an inferomedial direction. It descends as far as the medial side of the knee, passing behind the medial condyle of the femur to end in a tendon. This tendon curves anteriorly to join the tendons of the gracilis and semitendinous muscles which together form the pes anserinus, finally inserting into the proximal part of the tibia on the medial surface of its body. Sartorius comes from the Latin word sartor, meaning tailor, and it is sometimes called the tailor's muscle. There are four hypotheses as to the genesis of the name: One is that this name was chosen in reference to the cross-legged position in which tailors once sat. Another is that it refers to the location of the inferior portion of the muscle being the "inseam" or area of the inner thigh tailors commonly measure when fitting a pant. A third is that the muscle closely resembles a
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    76
    Trapezius muscle

    Trapezius muscle

    In human anatomy, the trapezius is a large superficial muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to the spine of the scapula (shoulder blade). Its functions are to move the scapulae and support the arm. The trapezius has three functional regions: the superior region (descending part), which supports the weight of the arm; the intermediate region (transverse part), which retracts the scapulae; and the inferior region (ascending part), which medially rotates and depresses the scapulae. The trapezius muscle resembles a trapezium (trapezoid in American English), or diamond-shaped quadrilateral. The word "spinotrapezius" refers to the human trapezius, although it is not commonly used in modern texts. In other mammals, it refers to a portion of the analogous muscle. The superior or upper fibers of the trapezius arise from the external occipital protuberance, the medial third of the superior nuchal line of the occipital bone (both in the back of the head), and the ligamentum nuchae. From this origin they proceed downward and laterally to be inserted into the posterior border of the lateral third of the clavicle. The middle
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    77
    Basal ganglia

    Basal ganglia

    The basal ganglia (or basal nuclei) are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas. The basal ganglia are associated with a variety of functions, including voluntary motor control, procedural learning relating to routine behaviors or "habits" such as bruxism, eye movements, and cognitive, emotional functions. Currently popular theories implicate the basal ganglia primarily in action selection, that is, the decision of which of several possible behaviors to execute at a given time. Experimental studies show that the basal ganglia exert an inhibitory influence on a number of motor systems, and that a release of this inhibition permits a motor system to become active. The "behavior switching" that takes place within the basal ganglia is influenced by signals from many parts of the brain, including the prefrontal cortex, which plays a key role in executive functions. The main components of the basal ganglia are the striatum, the globus pallidus, the substantia nigra, and the subthalamic nucleus.
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    78
    Bronchus

    Bronchus

    A bronchus (plural bronchi, adjective bronchial) is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles. No gas exchange takes place in this part of the lungs. The human trachea (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle and of the fifth thoracic vertebra or up to two vertebrae higher or lower, depending on breathing, at the anatomical point known as the carina. The right main bronchus is wider, shorter, and more vertical than the left main bronchus. The right main bronchus subdivides into three lobar bronchi, while the left main bronchus divides into two. The lobar bronchi divide into tertiary bronchi, also known as segmentalinic bronchi, each of which supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung separated from the rest of the lung by a connective tissue septum. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. There are ten segments per lung, but due to anatomic development, several segmental bronchi
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    79
    Canine tooth

    Canine tooth

    In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or (in the case of those of the upper jaw) eye teeth, are relatively long, pointed teeth. However, they can appear more flattened, causing them to resemble incisors and leading them to be called incisiform. They evolved and are used primarily for firmly holding food in order to tear it apart, and occasionally as weapons. They are often the largest teeth in a mammal's mouth. Most species that develop them normally have four per individual, two in the upper jaw and two in the lower, separated within each jaw by its incisors; humans and dogs are examples. In most animals, canines are the anterior-most teeth in the maxillary bone. The four canines in humans are the two maxillary canines and the two mandibular canines. There are four canine teeth: two in the upper (maxillary) and two in the lower (mandibular) arch. A canine is placed laterally to each lateral incisor. They are larger and stronger than the incisors, and their roots sink deeply into the bones, and cause well-marked prominences upon the surface. The crown is large and conical, very convex on its labial surface, a little hollowed and uneven
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    80
    Globus pallidus

    Globus pallidus

    The globus pallidus (Latin for "pale globe") also known as paleostriatum, is a sub-cortical structure of the brain. It is part of the telencephalon, but retains close functional ties with the subthalamus - both of which are part of the extrapyramidal motor system. The globus pallidus is a major component of the basal ganglia core along with the striatum and its direct target, the substantia nigra. The latter are made up of similar neuronal elements, have similar afferents from the dorsal striatum and have a similar synaptology; neither receives cortical afferents. The origin of the name is not established. It was known by Dejerine (1906) but not by Santiago Ramón y Cajal (1909–1911). As the elements in no way have the shape of a globe, Foix and Nicolesco (1925), the Vogts (1941), Crosby et al. (1962) followed by the Terminologia anatomica proposed the simpler term (neuter adjective) of pallidum ("pale"). For a long time the globus pallidus was linked to the putamen and termed the lentiform nucleus (nucleus lenticularis or lentiformis), a heterogeneous anatomical entity that is part of the striatum rather than the pallidum. The link with the substantia nigra pars reticulata was
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    81
    Leydig cell

    Leydig cell

    Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH). Leydig cells are polyhedral in shape, display a large prominent nucleus, an eosinophilic cytoplasm and numerous lipid-filled vesicles. Leydig cells are named after the German anatomist Franz Leydig, who discovered them in 1850. Leydig cells release a class of hormones called androgens (19-carbon steroids). They secrete testosterone, androstenedione and dehydroepiandrosterone (DHEA), when stimulated by the pituitary hormone luteinizing hormone (LH). LH increases cholesterol desmolase activity (an enzyme associated with the conversion of cholesterol to pregnenolone), leading to testosterone synthesis and secretion by Leydig cells. Prolactin (PRL) increases the response of Leydig cells to LH by increasing the number of LH receptors expressed on Leydig cells. The mammalian Leydig cell is a polyhedral epithelioid cell with a single eccentrically located ovoid nucleus. The nucleus contains one to three prominent nucleoli and large amounts of dark-staining peripheral heterochromatin. The acidophilic
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    82
    Malleus

    Malleus

    The malleus or hammer is a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum. The word is Latin for hammer. It transmits the sound vibrations from the eardrum to the incus. The malleus is unique to mammals, and evolved from a lower jaw bone in basal amniotes called the articular, which still forms part of the jaw joint in reptiles and birds. Embryologically it is derived from the first pharyngeal arch along with the rest of the bones of mastication, such as the maxilla and mandible. sound waves hit the ear drum and together with the other bones it tends to transit the vibrations from the ear drum to the cochlea to the brain so as to enable one to hear.
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    83
    Oropharynx

    Oropharynx

    The Oropharynx (oral part of the pharynx) reaches from the Uvula to the level of the hyoid bone. It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil. Although older resources have stated that Fusobacterium is a common occurrence in the human oropharynx, the current consensus is that Fusobacterium should always be treated as a pathogen. The name is formed from their initials: All of these organisms are part of the normal oropharyngeal flora, which grow slowly, prefer a carbon dioxide–enriched atmosphere and share an enhanced capacity to produce endocardial infections, especially in young children. Actinomyces species that cause human disease do not exist freely in nature but are normal flora of the oropharynx.
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    84
    Osteoblast

    Osteoblast

    Osteoblasts (from the Greek words for "bone" and "germ" or embryonic) are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin. Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen. Osteoblasts are also responsible for mineralization of this matrix. Zinc, copper and sodium are some of the minerals required in this process. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which are in charge of production of matrix and mineral, and osteoclasts, which break down the tissue. The number of osteoblasts tends to decrease with age, affecting the balance of formation and resorption in the bone tissue, and potentially leading to osteoporosis. Osteoblasts arise from osteoprogenitor cells located in the deeper layer of periosteum and the bone marrow. Osteoprogenitors are immature progenitor cells that express the master regulatory transcription factor Cbfa1/Runx2. Osteoprogenitors are induced to differentiate under the influence of growth factors, in particular the bone morphogenetic proteins
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    85
    Parietal lobe

    Parietal lobe

    The parietal lobe is a part of the brain positioned above (superior to) the occipital lobe and behind (posterior to) the frontal lobe. The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the dorsal stream of the visual system. This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions. The name derives from the overlying parietal bone, which is named from the Latin paries-, wall. The parietal lobe is defined by three anatomical boundaries: The central sulcus separates the parietal lobe from the frontal lobe; the parieto-occipital sulcus separates the parietal and occipital lobes; the lateral sulcus (sylvian fissure) is the most lateral boundary, separating it from the temporal lobe; and the medial longitudinal fissure divides the two hemispheres. Immediately posterior to the central sulcus, and the most anterior part of the parietal lobe, is the postcentral gyrus (Brodmann area 3), the secondary somatosensory cortical area. Dividing this and the posterior parietal cortex is the postcentral sulcus. The
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    86
    Profunda femoris artery

    Profunda femoris artery

    The profunda femoris artery (also known as the deep femoral artery, or the deep artery of the thigh) is a branch of the femoral artery that, as its name suggests, travels more deeply (posteriorly) than the rest of the femoral artery. The profunda femoris branches off the femoral artery soon after its origin. It travels down the thigh closer to the femur than the femoral artery, running between the pectineus and the adductor longus, and running on the posterior side of adductor longus. The deep femoral artery does not leave the thigh. The profunda femoris gives off the following branches: This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    87
    Prosencephalon

    Prosencephalon

    In the anatomy of the brain of vertebrates, the prosencephalon (or forebrain) is the rostral-most (forward-most) portion of the brain. The prosencephalon, the mesencephalon (midbrain), and rhombencephalon (hindbrain) are the three primary portions of the brain during early development of the central nervous system. It controls body temperature, reproductive functions, eating, sleeping, and any display of emotions. At the five-vesicle stage, the prosencephalon separates into the diencephalon (prethalamus, thalamus, hypothalamus, subthalamus, epithalamus, and pretectum) and the telencephalon (cerebrum). The cerebrum consists of the cerebral cortex, underlying white matter, and the basal ganglia. By 5 weeks in utero, it is visible as a single portion toward the front of the fetus. At 8 weeks in utero, the prosencephalon splits into the left and right cerebral hemispheres. When the embryonic prosencephalon fails to divide the brain into two lobes, it results in a condition known as holoprosencephaly.
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    88
    Subclavian artery

    Subclavian artery

    In human anatomy, the subclavian arteries are two major arteries of the upper thorax (chest), below the clavicle (collar bone). They receive blood from the top (arch) of the aorta. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplies blood to the right arm, with some branches supplying the head and thorax. The usual branches of the subclavian on both sides of the body are the vertebral artery, the internal thoracic artery, the thyrocervical trunk, the costocervical trunk and the dorsal scapular artery. The subclavian becomes the axillary artery at the lateral border of the first rib. From its origin, the subclavian artery travels laterally, passing between anterior and middle scalene muscles, with the anterior scalene (scalenus anterior) on its anterior side and the middle scalene (scalenus medius) on its posterior. This is in contrast to the subclavian vein, which travels anterior to the scalenus anterior. As the subclavian artery crosses the lateral border of the first rib, it becomes the axillary artery. These may be remembered by the mnemonic VITamin C and D. Embryologically, the left subclavian simply arises from the left 7th
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    89
    Tibia

    Tibia

    The tibia ( /ˈtɪbiə/), shinbone or shankbone, is the larger and stronger of the two bones in the leg below the knee in vertebrates (the other being the fibula), and connects the knee with the ankle bones. The tibia is named for the Greek aulos flute, also known as a tibia. It is commonly recognized as the strongest weightbearing bone of the body. The tibia is found next to the fibula on the medial side of the leg. It is the second largest bone next to the femur. In the male, its direction is vertical, and parallel with the bone of the opposite side. In the female, it has a slightly oblique direction downward and laterally, to compensate for the greater obliqueness of the femur. Studies are inconclusive, however. It is prismoid in form, expanded above, where it enters into the knee-joint, contracted in the lower third, and again enlarged but to a lesser extent towards the ankle joint. The superior tibiofibular articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. The inferior tibiofibular articulation (tibiofibular syndesmosis) is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough
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    90
    Hypoglossal nerve

    Hypoglossal nerve

    The hypoglossal nerve is the twelfth cranial nerve (XII), leading to the tongue. The nerve arises from the hypoglossal nucleus and emerges from the medulla oblongata in the preolivary sulcus separating the olive and the pyramid. It then passes through the hypoglossal canal. On emerging from the hypoglossal canal, it gives off a small meningeal branch and picks up a branch from the anterior ramus of C1. It spirals behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. After passing deep to the posterior belly of the digastric muscle, it passes to the submandibular region, passes lateral to the Hyoglossus muscle, and inferior to the lingual nerve to reach and efferently innervate the tongue. It supplies motor fibres to all of the muscles of the tongue, except the palatoglossus muscle, which is innervated by the vagus nerve (cranial nerve X) or, according to some classifications, by fibres from the glossopharyngeal nerve (cranial nerve IX) that "hitchhike" within the vagus. It controls tongue movements of speech, food manipulation, and swallowing. The hypoglossal nerve is derived from the basal plate of the
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    91
    Inferior nasal conchae

    Inferior nasal conchae

    The inferior nasal concha (inferior turbinated bone) is one of the turbinates in the nose. It extends horizontally along the lateral wall of the nasal cavity [Fig. 1] and consists of a lamina of spongy bone, curled upon itself like a scroll. Each inferior nasal concha is considered a facial pair of bones since they arise from the maxillae bones and projects horizontally into the nasal cavity. They are also termed 'inferior nasal turbinates' because they function similar to that of a turbine. As the air passes through the turbinates, the air is churned against these mucosa-lined bones in order to receive warmth, moisture and cleansing. Superior to inferior nasal concha are the middle nasal concha and superior nasal concha which arise from the cranial portion of the skull. Hence, these two are considered as a part of the cranial bones. It has two surfaces, two borders, and two extremities. The medial surface is convex, perforated by numerous apertures, and traversed by longitudinal grooves for the lodgement of vessels. The lateral surface is concave, and forms part of the inferior meatus. Its upper border is thin, irregular, and connected to various bones along the lateral wall of
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    92
    Zygomatic bone

    Zygomatic bone

    In the human skull, the zygomatic bone (cheekbone, malar bone) is a paired bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. The zygomatic is homologous to the jugal bone of other tetrapods. It is situated at the upper and lateral part of the face and forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal and infratemporal fossa. It presents a malar and a temporal surface; four processes, the frontosphenoidal, orbital, maxillary, and temporal; and four borders. The term zygomatic derives from the Greek Ζυγόμα zygoma meaning "yoke". The zygomatic bone is occasionally referred to as the zygoma, but this term may also refer to the zygomatic arch or the zygomatic process. The malar surface is convex and perforated near its center by a small aperture, the zygomaticofacial foramen, for the passage of the zygomaticofacial nerve and vessels; below this foramen is a slight elevation, which gives origin to the Zygomaticus. The temporal surface, directed posteriorly and medially, is concave, presenting medially a rough, triangular area, for articulation with the maxilla (articular
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    93
    Dorsal scapular nerve

    Dorsal scapular nerve

    The dorsal scapular nerve arises from the brachial plexus, usually from the plexus root (anterior/ventral ramus) of C5. It provides motor innervation to the rhomboid muscles, which pull the scapula towards the spine and levator scapulae muscle, which elevates the scapula. Injury to this nerve is usually apparent when the scapula on one side is located farther from the midline. Once the nerve leaves C5 it commonly pierces the middle scalene muscle, and continues deep to levator scapulae and the rhomboids. It is accompanied by the one of two arteries. Either the dorsal scapular artery (the only artery that comes off of the third part of subclavian when present, although its origin is highly variable in different people) or when the dorsal scapular artery is absent, it is accompanied by the deep branch of the transverse cervical artery (an artery coming off of the thyrocervical trunk, a branch of the first part of the subclavian artery, the other two branches being vertebral artery and internal thoracic artery).
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    94
    Duodenum

    Duodenum

    The duodenum /ˌduːəˈdinəm/ is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum. In mammals the duodenum may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest part of the small intestine, where most chemical digestion takes place. The name duodenum is from the Latin duodenum digitorum, or "twelve fingers' breadth". In humans, the duodenum is a hollow jointed tube about 10–15 inches (25–38 centimetres) long connecting the stomach to the jejunum. It begins with the duodenal bulb and ends at the ligament of Treitz. The duodenum is largely responsible for the breakdown of food in the small intestine, using enzymes. Brunner's glands, which secrete mucus, are found in the duodenum. The duodenum wall is composed of a very thin layer of cells that form the muscularis mucosae. The duodenum is almost entirely retroperitoneal. The duodenum also regulates the rate of emptying of the stomach via hormonal pathways. Secretin and
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    95
    Endoderm

    Endoderm

    Endoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer), with the endoderm as the intermost layer. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of multiple systems. The following chart shows the products produced by the endoderm. Liver and pancreas cells are believed to derive from a common precursor. In humans,the endoderm can differentiate into distinguishable organs after 5 weeks of embryonic development. This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    96
    Entorhinal cortex

    Entorhinal cortex

    The entorhinal cortex (EC) (ento = interior, rhino = nose, entorinal = interior to the rhinal sulcus) is located in the medial temporal lobe and functions as a hub in a widespread network for memory and navigation. The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in autobiographical/declarative/episodic memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning, the association of impulses from the eye and the ear occurs in the entorhinal cortex. In rodents, the EC is located at the caudal end of the temporal lobe. In primates it is located at the rostral end of the temporal lobe and stretches dorsolaterally. It is usually divided into medial and lateral regions with three bands with distinct properties and connectivity running perpendicular across the whole area. A distinguishing characteristic of the EC is the lack of cell bodies where layer IV should be; this layer is called the lamina
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    97
    Vestibulocochlear nerve

    Vestibulocochlear nerve

    The vestibulocochlear nerve (auditory vestibular nerve) is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain. The acoustic nerve is derived from the embryonic otic placode. This is the nerve along which the sensory cells (the hair cells) of the inner ear transmit information to the brain. It consists of the cochlear nerve, carrying information about hearing, and the vestibular nerve, carrying information about balance. It emerges from the pons and exits the inner skull via the internal acoustic meatus (or internal auditory meatus) in the temporal bone. The vestibulocochlear nerve consists mostly of bipolar neurons and splits into two large divisions: the cochlear nerve and the vestibular nerve. The cochlear nerve travels away from the cochlea of the inner ear where it starts as the spiral ganglia. Processes from the organ of Corti conduct afferent transmission to the spiral ganglia. It is the inner hair cells of the organ of Corti that are responsible for activation of afferent receptors in response to pressure waves reaching the basilar membrane through the transduction of sound. The
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    98
    Epididymis

    Epididymis

    The epididymis ( /ɛpɨˈdɪdɨmɪs/; plural: epididymides /ɛpɨˌdɪdɨˈmiːdiːz/) is part of the male reproductive system and is present in all male amniotes. It is a single, narrow, tightly-coiled tube (in adult humans, six to seven meters in length) connecting the efferent ducts from the rear of each testicle to its vas deferens. A similar, but probably non-homologous, structure is found in cartilaginous fishes. The epididymis can be divided into three main regions: In reptiles, there is an additional canal between the testis and the head of the epididymis,which is painful when hit and which receives the various efferent ducts. This is, however, absent in all birds and mammals. The epididymis is covered by a two layered pseudostratified epithelium. The epithelium is separated by a basement membrane from the connective tissue wall which has smooth muscle cells. The major cell types in the epithelium are: Spermatozoa formed in the testis enter the caput epididymis, progress to the corpus, and finally reach the cauda region, where they are stored. Sperm entering the caput epididymis are incomplete - they lack the ability to swim forward (motility) and to fertilize an egg. It stores the sperm
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    Lumbricals of the hand

    Lumbricals of the hand

    The lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints and extend the interphalangeal joints. There are four of these small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone. Instead they attach proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions. The first and second lumbricals (the most radial two) are innervated by the median nerve. The third and fourth lumbricals (most ulnar two) are innervated by the deep branch of the ulnar nerve. This is the usual innervation of the lumbricals (occurring in 60% of individuals). However 1:3 (median:ulnar - 20% of individuals) and 3:1 (median:ulnar - 20% of individuals) also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit of flexor digitorum profundus (i.e. if the muscle units supplying the tendon to the middle finger are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve). There are four separate sources of blood supply for these muscles: the superficial palmar arch, the common palmar digital artery, the deep palmar arch,
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    Median nerve

    Median nerve

    The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve is formed from parts of the medial and lateral cords of the brachial plexus, and continues down the arm to enter the forearm with the brachial artery. It is formed from contributions from the lateral and medial cords of the brachial plexus, originating from ventral roots of C5 & C6 (lateral cord) and C8 & T1 (medial cord). The median nerve is the only nerve that passes through the carpal tunnel. Carpal tunnel syndrome is the disability that results from the median nerve being pressed in the carpal tunnel. After receiving inputs from both the lateral and medial cords of the brachial plexus, the median nerve enters the arm from axilla at the inferior margin of the teres major muscle. it then passes vertically down and courses with brachial artery on medial side of arm between biceps brachii and brachialis. At first lateral to the artery and lies anterior to the elbow joint, it then crosses anteriorly to run medial to the artery in the distal arm and into the cubital fossa. Inside the cubital fossa the median nerve
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    Outer ear

    Outer ear

    The outer ear is the external portion of the ear, which consists of the pinna, concha, and external auditory meatus. It gathers sound energy and focuses it on the eardrum (tympanic membrane). One consequence of the configuration of the external ear is to selectively boost the sound pressure 30- to 100-fold for frequencies around 3 kHz. This amplification makes humans most sensitive to frequencies in this range - and also explains why they are particularly prone to acoustical injury and hearing loss near this frequency. Most human speech sounds are also distributed in the bandwidth around 3 kHz. The visible part is called the pinna. It is composed of a thin plate of yellow elastic cartilage, covered with integument, and connected to the surrounding parts by ligaments and muscles; and to the commencement of the external acoustic meatus by fibrous tissue. Many mammals can move the pinna (with the auriculares muscles) in order to focus their hearing in a certain direction in much the same way that they can turn their eyes. Most humans, unlike most other mammals, do not have this ability. From the pinna the sound pressure waves move into the ear canal, a simple tube running through the
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    Cauda equina

    Cauda equina

    The cauda equina is a bundle of nerves occupying the spinal column below the spinal cord in most vertebrates that consists of nerve roots and rootlets attached to the spinal cord. It serves the legs. In humans, because the spinal cord stops growing in infancy while the bones of the spine continue growing, the spinal cord in adults ends at about the level of the vertebra L1/L2, and at birth at L3. However there is some variation in adults and the cord may end anywhere between vertebrae T12 to L3. Individual spinal nerve roots arise from the spinal cord as they do closer to the head, but as the differential growth occurs the top end of the nerve stays attached to the spinal cord and the lower end of the nerve exits the spinal column at its proper level, this results in a "bundle"-like structure of nerve fibres that extends caudally from the end of the spinal cord, gradually declining in number further down as individual pairs leave the spinal column. At the base of the Cauda Equina, there are approximately 10 fiber pairs, 3-5 lumbar, 5 sacral, and the single coccygeal nerve. All these roots and rootlets down the vertebral column give the appearance of a horse's tail, which is the
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    103
    Pancreas

    Pancreas

    The pancreas /ˈpæŋkriəs/ is a gland organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, somatostatin, and pancreatic polypeptide, and a digestive organ, secreting pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme. Under a microscope, stained sections of the pancreas reveal two different types of parenchymal tissue. Lightly staining clusters of cells are called islets of Langerhans, which produce hormones that underlie the endocrine functions of the pancreas. Darker-staining cells form acini connected to ducts. Acinar cells belong to the exocrine pancreas and secrete digestive enzymes into the gut via a system of ducts. The pancreas is a dual-function gland, having features of both endocrine and exocrine glands. The part of the pancreas with endocrine function is made up of approximately a million cell clusters called islets of Langerhans. Four main cell types exist in the islets. They are relatively
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    104
    Claustrum

    Claustrum

    The claustrum is a thin, irregular, sheet of neurons which is attached to the underside of the neocortex in the center of the brain. It is suspected to be present in the brains of all mammals. The claustrum is a fraction of a millimetre to a few millimetres deep, and is a vertical curved sheet of subcortical gray matter oriented sagittally between the white matter tracts of the external capsule and extreme capsule. The claustrum is lateral to the putamen and medial to the insular cortex and is considered by some sources to be part of the basal ganglia. There are lateral and medial tracts connecting the claustrum to many parts of the cortex and perhaps to the hippocampus, the amygdala, and the caudate nucleus (connections with subcortical centers are a matter of debate). One of the interesting features of the claustrum is the uniformity in the types of cells, indicating a uniform type of processing by all claustral neurons. Though organized into modality specific regions, the claustrum contains a great deal of longitudinal connections between its neurons that could serve to synchronize the entire anterior-posterior extent of the claustrum. Francis Crick and Christof Koch have
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    105
    Epiglottis

    Epiglottis

    The epiglottis is a flap that is made of elastic cartilage tissue covered with a mucous membrane, attached to the entrance of the larynx. It projects obliquely upwards behind the tongue and the hyoid bone, pointing dorsally. The term, like tonsils, is often incorrectly used to refer to the uvula. There are taste buds on the epiglottis. The epiglottis guards the entrance of the glottis, the opening between the vocal folds. It is normally pointed upward while one is breathing with its underside functioning as part of the pharynx, but while one is swallowing, elevation of the hyoid bone draws the larynx upward; as a result, the epiglottis folds down to a more horizontal position, with its superior side functioning as part of the pharynx. In this manner it prevents food from going into the trachea and instead directs it to the esophagus, which is posterior. The epiglottis is one of nine cartilaginous structures that make up the larynx (voice box). While one is breathing, it lies completely within the pharynx. When one is swallowing it serves as part of the anterior of the larynx. In some languages, the epiglottis is used to produce speech sounds, though this sound-type is rather rare.
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    Frontal bone

    Frontal bone

    The frontal bone is a bone in the human skull. The name comes from the Latin word frons (meaning "forehead"). The bone resembles a cockleshell in form, and consists of three portions: The frontal bone is presumed to be derived from neural crest cells. The border of the squama frontalis is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the sphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid. In most vertebrates, the frontal bone is paired, rather than presenting the single, fused structure found in humans. It typically lies on the upper part of the head, between the eyes, but in many non-mammalian animals it does not form part of the orbital cavity. Instead, in reptiles, bony fish and amphibians it is often separated from the orbits by one or two additional bones not found in mammals. These bones, the prefrontals and
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    107
    Pubic symphysis

    Pubic symphysis

    The pubic symphysis or symphysis pubis is the midline cartilaginous joint (secondary cartilaginous) uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis. In males, the suspensory ligament of the penis attaches to the pubic symphysis. In females, the pubic symphysis is intimately close to the clitoris. In normal adults it can be moved roughly 2 mm and with 1 degree rotation. This increases for women at the time of child birth. Symphysis pubis is a nonsynovial amphiarthrodial joint, and comes from the Greek word "symphysis", meaning growing together. The anterior width of the symphysis pubis is 3-5 mm greater than its intrapelvic posterior width. This joint is connected by fibrocartilage and may contain a fluid filled cavity; the center is avascular, possibly due to the nature of the compressive forces passing through this joint, which may lead to harmful vascular disease. The ends of both pubic bones are covered by a thin layer of hyaline cartilage attached to the fibrocartilage. The fibrocartilaginous disk is reinforced
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    Subarachnoid space

    Subarachnoid space

    In the central nervous system, the subarachnoid cavity (subarachnoid space) is the interval between the arachnoid membrane and pia mater. It is occupied by spongy tissue consisting of trabeculae (delicate connective tissue filaments that extend from the arachnoid mater and blend into the pia mater) and intercommunicating channels in which the cerebrospinal fluid is contained. This cavity is small on the surface of the hemispheres of the brain. On the summit of each gyrus the pia mater and the arachnoid are in close contact, but in the sulci between the gyri, triangular spaces are left, in which the subarachnoid trabecular tissue is found. Whilst the pia mater closely follows the surface of the brain and dips into the sulci, the arachnoid bridges across them from gyrus to gyrus. At certain parts of the base of the brain, the arachnoid is separated from the pia mater by wide intervals, which communicate freely with each other and are named subarachnoid cisternæ; in these the subarachnoid tissue is less abundant. The subarachnoid space is the location of the interface between the vascular tissue and the cerebrospinal fluid and is active in the blood brain barrier. The arachnoid mater
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    Sympathetic nervous system

    Sympathetic nervous system

    The (ortho-) sympathetic nervous system (SNS) is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response. It is, however, constantly active at a basic level to maintain homeostasis. Alongside the other two components of the autonomic nervous system, the sympathetic nervous system aids in the control of most of the body's internal organs. Stress—as in the flight-or-fight response—is thought to counteract the parasympathetic system, which generally works to promote maintenance of the body at rest. In truth, the functions of both the parasympathetic and sympathetic nervous systems are not so straightforward, but this is a useful rule of thumb. There are two kinds of neurons involved in the transmission of any signal through the sympathetic system; pre- and post- ganglionic. The shorter preganglionic neurons originate from the thoracolumbar region of the spinal cord (levels T1 - L2, specifically) and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron. From there, the long postganglionic
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    110
    Choroid

    Choroid

    The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The structure of the choroid is generally divided into four layers: There are two circulations of the eye: the retinal and uveal, supplied in humans by posterior ciliary arteries, originating from the ophthalmic artery. The arteries of the uveal circulation, supplying the uvea and outer and middle layers of the retina, are branches of the ophthalmic artery and enter the eyeball without passing with the optic nerve. The retinal circulation, on the other hand, derives its circulation from the central retinal artery, also a branch of the ophthalmic artery, but passing in conjunction with the optic nerve. They are branching in a segmental distribution to the end arterioles and not anastomoses. This is clinically significant for diseases affecting
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    Brachiocephalic artery

    Brachiocephalic artery

    The brachiocephalic artery (or brachiocephalic trunk or innominate artery) is an artery of the mediastinum that supplies blood to the right arm and the head and neck. It is the first branch of the aortic arch, and soon after it emerges, the brachiocephalic artery divides into the right common carotid artery and the right subclavian artery. There is no brachiocephalic artery for the left side of the body. The left common carotid, and the left subclavian artery, come directly off the aortic arch. However, there are two brachiocephalic veins. It arises, on a level with the upper border of the second right costal cartilage, from the commencement of the arch of the aorta, on a plane anterior to the origin of the left carotid; it ascends obliquely upward, backward, and to the right to the level of the upper border of the right sternoclavicular articulation, where it divides into the right common carotid and right subclavian arteries. The artery then crosses the trachea in front of it obliquely from the left to the right, roughly at the middle of the trachea or the level of the ninth tracheal cartilage. In infants, it often divides cephalad to the sternoclavicular articulation, within the
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    112
    Choroid plexus

    Choroid plexus

    The choroid plexus (from Greek khorion "membrane enclosing the fetus, afterbirth"; "plexus": Mod.L., lit. "braid, network") is a structure in the ventricles of the brain where cerebrospinal fluid (CSF) is produced. The choroid plexus consists of modified ependymal cells. Choroid plexus is present in all components of the ventricular system except for the cerebral aqueduct, frontal horn of the lateral ventricle, and occipital horn of the lateral ventricle. It is found in the superior part of the inferior horn of the lateral ventricles. It follows up along this boundary, continuous with the inferior of the body of the lateral ventricles. It passes into the interventricular foramen, and is present at the top of the third ventricle. There is also choroid plexus in the fourth ventricle, in the section closest to the bottom half of the cerebellum. The choroid plexus (CP) consists of many capillaries, separated from the ventricles by choroid epithelial cells. Liquid filters through these cells from blood to become cerebrospinal fluid. There is also much active transport of substances into, and out of, the CSF as it is made. There are four choroid plexi in the brain, one in each of the
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    Jejunum

    Jejunum

    The jejunum (/dʒiːˈdʒuːnəm/) is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of jejunum. The jejunum lies between the duodenum and the ileum. The change from the duodenum to the jejunum is usually defined as the Duodenojejunal flexure and is attached, and thus "hung up", to the ventricle (see stomach) by the ligament of Treitz. In adult humans, the small intestine is usually between 5.5 and 6m long, 2.5m of which is the jejunum. The pH in the jejunum is usually between 7 and 9 (neutral or slightly alkaline). If the jejunum is impacted by blunt force the emesis reflex will be initiated. The jejunum and the ileum are suspended by mesentery which gives the bowel great mobility within the abdomen. It also contains circular and longitudinal smooth muscle which helps to move food along by a process known as peristalsis. The jejunum is the second portion of the small intestine, and it has a lining which is specialized in the absorption of carbohydrates and proteins. The proteins have been broken down
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    Mandible

    Mandible

    In vertebrates, the mandible, lower jaw or jawbone is a bone forming the skull with the cranium. In lobe-finned fishes and the early fossil tetrapods, the bone homologous to the mandible of mammals is merely the largest of several bones in the lower jaw. In such animals, it is referred to as the dentary bone, and forms the body of the outer surface of the jaw. It is bordered below by a number of splenial bones, while the angle of the jaw is formed by a lower angular bone and a suprangular bone just above it. The inner surface of the jaw is lined by a prearticular bone, while the articular bone forms the articulation with the skull proper. Finally a set of three narrow coronoid bones lie above the prearticular bone. As the name implies, the majority of the teeth are attached to the dentary, but there are commonly also teeth on the coronoid bones, and sometimes on the prearticular as well. This complex primitive pattern has, however, been simplified to various degrees in the great majority of vertebrates, as bones have either fused or vanished entirely. In teleosts, only the dentary, articular, and angular bones remain, while in living amphibians, the dentary is accompanied only by
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    115
    Pulmonary artery

    Pulmonary artery

    The pulmonary artery carries deoxygenated blood from the heart to the lungs. It is one of the only arteries (other than the umbilical arteries in the fetus) that carry deoxygenated blood. In the human heart, the pulmonary trunk (pulmonary artery or main pulmonary artery) begins at the base of the right ventricle. It is short and wide - approximately 5 cm (2 inches) in length and 3 cm (1.2 inches) in diameter. It then branches into two pulmonary arteries (left and right), which deliver de-oxygenated blood to the corresponding lung. In contrast to the pulmonary arteries, the bronchial arteries supply nutrition to the lungs themselves. Pulmonary hypertension occurs alone and as a consequence of a number of lung diseases. It can also be a consequence of heart disease (Eisenmenger's syndrome) but equally a cause (right-ventricular heart failure); it also occurs as a consequence of pulmonary embolism and scleroderma. It is characterised by reduced exercise tolerance. Severe forms, generally, have a dismal prognosis.
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    Thalamus

    Thalamus

    The thalamus (from Greek θάλαμος, "inner chamber") is a midline symmetrical structure within the brains of vertebrates including humans, situated between the cerebral cortex and midbrain. Its function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness. The thalamus surrounds the third ventricle. It is the main product of the embryonic diencephalon. The thalamus is perched on top of the brainstem, near the center of the brain, with nerve fibers projecting out to the cerebral cortex in all directions. The medial surface of the thalamus constitutes the upper part of the lateral wall of the third ventricle, and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the Interthalamic adhesion. Both parts of this structure of the brain in the human are each about the size and shape of a walnut. These are about three centimetres in length, at the widest part 2.5 centimetres across and about 2 centimetres in height (the nut relative to an unshelled nut with the nut-shell join in the horizontal plane). The two halves of the thalamus are prominent bulb-shaped masses, about
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    Incus

    Incus

    The incus or anvil is the anvil-shaped small bone or ossicle in the middle ear. Incus means "anvil" in Latin. It connects the malleus to the stapes. It was first described by Alessandro Achillini of Bologna. The incus transmits sound vibrations from the malleus to the stapes. The Anatomy Wiz Incus
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    Ischiocavernosus muscle

    Ischiocavernosus muscle

    The ischiocavernosus muscle is a muscle just below the surface of the perineum, present in both men and women. It helps flex the anus, and (in males) stabilize the erect penis or (in females) tense the vagina during orgasm. Kegel exercises (also known as pelvic floor exercises) can help tone the ischiocavernosus muscle. Ischiocavernosus compresses the crus penis, and retards the return of the blood through the veins, and thus serves to maintain the organ erect. It arises by tendinous and fleshy fibers from the inner surface of the tuberosity of the ischium, behind the crus penis; and from the rami of the pubis and ischium on either side of the crus. From these points fleshy fibers succeed, and end in an aponeurosis which is inserted into the sides and under surface of the crus penis. This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    Knee

    Knee

    The knee joint joins the thigh with the lower leg and consists of two articulations: one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus (a pivotal hinge joint), which permits flexion and extension as well as a slight medial and lateral rotation. Since in humans the knee supports nearly the whole weight of the body, it is vulnerable to both acute injury and the development of osteoarthritis. It is often grouped into tibiofemoral and patellofemoral components. (The fibular collateral ligament is often considered with tibiofemoral components.) The knee is a hinge type synovial joint, which is composed of three functional compartments: the femoropatellar articulation consists of the patella, or "kneecap", and the patellar groove on the front of the femur through which it slides; and the medial and lateral femorotibial articulations linking the femur, or thigh bone, with the tibia, the main bone of the lower leg. The joint is bathed in synovial fluid which is contained inside the synovial membrane called the joint capsule. The posterolateral corner of the knee is
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    Phrenic nerve

    Phrenic nerve

    The phrenic nerve is a nerve that originates in the neck and passes down between the lung and heart to reach the diaphragm. It is important for breathing, as it passes motor information to the diaphragm and receives sensory information from it. There are two phrenic nerves, a left and a right one. The phrenic nerve originates mainly from the 4th cervical nerve, but also receives contributions from the 5th and 3rd cervical nerves (C3-C5) in humans. The phrenic nerves contain motor, sensory, and sympathetic nerve fibers. These nerves provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura and pericardium. The phrenic nerve descends obliquely with the Internal Jugular Vein across the anterior scalene, deep to the prevertebral layer of deep cervical fascia and the transverse cervical and suprascapular arteries. On the left, the phrenic nerve crosses anterior to the first part of the subclavian artery. On the right, it lies on the anterior scalene muscle and crosses anterior to the 2nd part of the subclavian artery. On both sides, the phrenic nerve runs posterior to the subclavian vein
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    Prostate

    Prostate

    The prostate (from Greek προστάτης - prostates, literally "one who stands before", "protector", "guardian") is a compound tubuloalveolar exocrine gland of the male reproductive system in most mammals. In 2002, female paraurethral glands, or Skene's glands, were officially renamed the female prostate by the Federative International Committee on Anatomical Terminology. The prostate differs considerably among species anatomically, chemically, and physiologically. The function of the prostate is to secrete a slightly acidic fluid, milky or white in appearance, that usually constitutes 20–30% of the volume of the semen along with spermatozoa and seminal vesicle fluid. Semen is made alkaline overall with the secretions from the other contributing glands, including, at least, the seminal vesicle fluid. The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. The alkalinization of semen is primarily accomplished through secretion from the seminal vesicles. The prostatic fluid is expelled in the first ejaculate fractions, together with most of the spermatozoa. In comparison with the few spermatozoa expelled together with mainly seminal
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    Sphenoid bone

    Sphenoid bone

    The sphenoid bone (/ˈsfiːnɔɪd/; from Greek sphenoeides, "wedgelike") is an unpaired bone situated at the front middle of the skull in front of the temporal bone and basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the orbit. Its shape somewhat resembles that of a butterfly or bat with its wings extended. It is divided into the following parts: Two sphenoidal conchae are situated at the anterior and posterior part of the body. The sphenoid bone of humans is homologous with a number of bones that are often separate in other animals, and have a somewhat complex arrangement. In the early lobe-finned fishes and tetrapods, the pterygoid bones were flat, wing-like bones forming the major part of the roof of the mouth. Above the pterygoids were the epipterygoid bones, which formed part of a flexible joint between the braincase and the palatal region, as well as extending a vertical bar of bone towards the roof of the skull. Between the pterygoids lay an elongated, narrow parasphenoid bone, which also spread over some of the lower surface of the braincase, and connected, at its forward end, with a sphenethmoid bone helping to protect
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    Extensor hallucis longus muscle

    Extensor hallucis longus muscle

    The Extensor hallucis longus is a thin muscle, situated between the Tibialis anterior and the Extensor digitorum longus that functions to extend the big toe, dorsiflex the foot, and assists with foot inversion. It arises from the anterior surface of the fibula for about the middle two-fourths of its extent, medial to the origin of the Extensor digitorum longus; it also arises from the interosseous membrane to a similar extent. The anterior tibial vessels and deep peroneal nerve lie between it and the Tibialis anterior. The fibers pass downward, and end in a tendon, which occupies the anterior border of the muscle, passes through a distinct compartment in the cruciate crural ligament, crosses from the lateral to the medial side of the anterior tibial vessels near the bend of the ankle, and is inserted into the base of the distal phalanx of the great toe. Opposite the metatarsophalangeal articulation, the tendon gives off a thin prolongation on either side, to cover the surface of the joint. An expansion from the medial side of the tendon is usually inserted into the base of the proximal phalanx. Occasionally united at its origin with the Extensor digitorum longus. Extensor ossis
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    Great saphenous vein

    Great saphenous vein

    The great saphenous vein (GSV), also long saphenous vein, is the large (subcutaneous) superficial vein of the leg and thigh. The terms "safaina" (Greek, meaning "manifest," "to be clearly seen") and "el safin" (Arabic, meaning "hidden/concealed") have both been claimed as the origin for the word "saphenous." The GSV originates from where the dorsal vein of the first digit (the large toe) merges with the dorsal venous arch of the foot. After passing anterior to the medial malleolus (where it often can be visualized and palpated), it runs up the medial side of the leg. At the knee, it runs over the posterior border of the medial epicondyle of the femur bone. The great saphenous vein then courses laterally to lie on the anterior surface of the thigh before entering an opening in the fascia lata called the saphenous opening. It joins with the femoral vein in the region of the femoral triangle at the saphenofemoral junction. At the ankle it receives branches from the sole of the foot through the medial marginal vein; in the lower leg it anastomoses freely with the small saphenous vein, communicates with the anterior and posterior tibial veins and receives many cutaneous veins; in the
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    Metacarpus

    Metacarpus

    In human anatomy, the metacarpus is the intermediate part of the hand skeleton that is located between the phalanges (bones of the fingers) and the carpus which forms the connection to the forearm. The metacarpus consists of metacarpal bones. Its equivalent in the foot is the metatarsus. The metacarpals form a transverse arch to which the rigid row of distal carpal bones are fixed. The peripheral metacarpals (those of the thumb and little finger) form the sides of the cup of the palmar gutter and as they are brought together they deepen this concavity. The index metacarpal is the most firmly fixed, while the thumb metacarpal articulates with the trapezium and acts independently from the others. The middle metacarpals are tightly united to the carpus by intrinsic interlocking bone elements at their bases. The ring metacarpal forms a transitional element of the semi-independent last metacarpal. Each metacarpal bone consists of a body and two extremities. The body (corpus; shaft) is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front. It presents three surfaces: medial, lateral, and dorsal. The base or carpal extremity (basis) is of
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    Trapezium

    Trapezium

    The trapezium bone (greater multangular bone) is a carpal bone in the wrist. It forms the radial border of the carpal tunnel. The trapezium is distinguished by a deep groove on its anterior surface. It is situated at the radial side of the carpus, between the scaphoid and the first metacarpal bone (the metacarpal bone of the thumb). It is homologous with the first distal carpal of reptiles and amphibians. The etymology derives from the Greek trapezion which means "irregular quadrilateral;" literally, "a little table," from trapeza meaning table. Also, from tra- "four" and peza "foot" or "edge." The superior surface is directed upward and medialward; medially it is smooth, and articulates with the scaphoid; laterally it is rough and continuous with the lateral surface. The inferior surface is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base of the first metacarpal bone. This saddle-shaped articulation is partially responsible for the thumb's opposable motion. The dorsal surface is smooth. The palmar surface is narrow and rough. At its upper part is a deep groove, running from above obliquely downward
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    Abducent nerve

    Abducent nerve

    The abducens nerve or abducent nerve (the sixth cranial nerve, also called the sixth nerve or simply VI) is a somatic efferent nerve that controls the movement of a single muscle, the lateral rectus muscle of the eye, in humans. In most other mammals it also innervates the musculus retractor bulbi, which can retract the eye for protection. Homologous abducens nerves are found in all vertebrates except lampreys and hagfishes. The human CN VI is derived from the basal plate of the embryonic pons. The Latin name for the sixth cranial nerve is nervus abducens. The Terminologia Anatomica officially recognizes two different English translations: abducent nerve and abducens nerve. Either term is correct. “Abducens” is more common in recent literature, while “abducent” predominates in the older literature. The United States National Library of Medicine uses “abducens nerve” in its Medical Subject Heading (MeSH) vocabulary to index the vast MEDLINE and PubMed biomedical databases. The 39th edition of Gray’s Anatomy (2005) also prefers “abducens nerve.” The abducens nerve leaves the brainstem at the junction of the pons and the medulla, medial to the facial nerve. In order to reach the eye,
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    Flexor digitorum superficialis muscle

    Flexor digitorum superficialis muscle

    Flexor digitorum superficialis (flexor digitorum sublimis) is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest part of the superficial layer of this compartment, and sometimes considered to be a distinct, "intermediate layer" of this compartment. It is relatively common for the Flexor digitorum superficialis to be missing from the little finger, bilaterally and unilaterally, which can cause problems when diagnosing a little finger injury. The muscle has two classically described heads - the humeroulnar and radial - and it is between these heads that the median nerve and ulnar artery pass. The ulnar collateral ligament of elbow joint gives its origin to part of this muscle. Four long tendons come off this muscle near the wrist and travel through the carpal tunnel formed by the flexor retinaculum. These tendons, along with those of flexor digitorum profundus, are enclosed by a common flexor sheath. The tendons attach to the anterior margins on the bases of the middle phalanges of the four fingers. These tendons have a split (Camper's Chiasm) at the end of
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    Acromion process

    Acromion process

    In human anatomy, the acromion (from Greek: akros, "highest", ōmos, "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade), together with the coracoid process extending laterally over the shoulder joint. The acromion is a continuation of the scapular spine, and hooks over anteriorly. It articulates with the clavicle (collar bone) to form the acromioclavicular joint. The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity. Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concave. Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the deltoid. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the trapezius, and presents about its center a small oval surface for articulation with the acromial end of the
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    Brachial plexus

    Brachial plexus

    The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5-C8, T1). It proceeds through the neck, the axilla (armpit region), and into the arm. It is a bunch of nerves passing through the cervico-axillary canal to reach axilla and supplies brachium, antebrachium and hand. The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla innervated by the intercostobrachial nerve. Lesions can lead to severe functional impairment. The brachial plexus is divided into Roots, Trunks, Divisions, Cords, and Branches. There are five "terminal" branches and numerous other "pre-terminal" or "collateral" branches that leave the plexus at various points along its length. Bold indicates primary spinal root component of nerve. Italics indicate spinal roots that frequently, but not always, contribute to the nerve. Some mnemonics for remembering the branches:
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    Femoral artery

    Femoral artery

    The femoral artery (Latin: arteria femoralis) is a large artery in the thigh. It begins at the inguinal ligament (femoral head). In this segment, it is also called the common femoral artery (arteria femoralis communis) and gives the deep femoral artery, which provides blood to the thigh. After the branching of the deep femoral artery, it is called the superficial femoral artery (arteria femoralis superficialis) in clinical parlance, because of its superficial course. It continues along the femur to provide blood to the arteries that circulate the knee and the foot and enters the adductor canal. After it emerges from it through the adductor hiatus, it is named the popliteal artery. The femoral arteries receive blood through the external iliac artery. This connection occurs at the femoral triangle behind the inguinal ligament, which is usually near the head of the femur bone. That proximal section of the femoral artery, known specifically as the common femoral artery (CFA), leaves the femoral triangle through an apex beneath the sartorius muscle. It then divides into a deep femoral artery, more commonly known as the Profunda, which provides blood to the thigh, and the superficial
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    Femur

    Femur

    The femur (pl. femurs or femora), or thigh bone, is the most proximal (closest to the center of the body) bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in the rear legs. The femur is the largest bone in the human body. The head of the femur articulates with the acetabulum. By most measures the femur is one of the strongest bones in the body. In primitive tetrapods, the main points of muscle attachment along the femur are the internal trochanter and fourth trochanter, and a ridge along the ventral surface of the femoral shaft referred to as the adductor crest. The neck of the femur is generally minimal or absent in the most primitive forms, reflecting a simple attachment to the acetabulum. The greater trochanter was present in the extinct archosaurs, as well as in modern birds and mammals, being associated with the loss of the primitive sprawling gait. The lesser trochanter is a unique development of mammals, which lack both the internal and fourth trochanters. The adductor crest is also
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    Glossopharyngeal nerve

    Glossopharyngeal nerve

    The glossopharyngeal nerve is the ninth (IX) of twelve pairs of cranial nerves (24 nerves total). It exits the brainstem out from the sides of the upper medulla, just rostral (closer to the nose) to the vagus nerve. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest. There are a number of functions of the glossopharyngeal nerve: (From: inferior salivary nucleus - through jugular foramen - tympanic n.(of Jacobson)- lesser petrosal n. - through foramen ovale - Otic ganglion (Pre-Ganglionic Parasympathetic fibers synapse, to start Post-Ganglionic Parasympathetic fibers) - Auriculotemporal n.(Parasympathetics hitchhikes to reach Parotid gland) The glossopharyngeal nerve consists of five components with distinct functions: Branchial motor (special visceral efferent) - supplies the stylopharyngeus muscle. Visceral motor (general visceral efferent) provides parasympathetic innervation of the parotid gland. Visceral sensory (general visceral afferent) carries visceral sensory information from the carotid sinus and body. General sensory (general somatic
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    Large intestine

    Large intestine

    The large intestine (or large bowel) is the last part of the digestive system in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body. This article is primarily about the human gut, though the information about its processes are directly applicable to most mammals. The large intestine consists of the cecum, colon, rectum and anal canal. It starts in the right iliac region of the pelvis, just at or below the right waist, where it is joined to the bottom end of the small intestine. From here it continues up the abdomen, then across the width of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus. The large intestine is about 4.9 feet (1.5 m) long, which is about one-fifth of the whole length of the intestinal canal. In Terminologia Anatomica the large intestine includes the cecum, colon, rectum, and anal canal. However, some sources exclude the anal canal. The large intestine takes about 16 hours to finish the digestion of the food. The colon absorbs vitamins which are created by the colonic bacteria - such as vitamin K (especially important as the daily
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    Nasal cavity

    Nasal cavity

    The nasal cavity (or nasal fossa) is a large air filled space above and behind the nose in the middle of the face. The nasal cavity conditions the air to be received by the other areas of the respiratory tract. Owing to the large surface area provided by the nasal conchae, the air passing through the nasal cavity is warmed or cooled to within 1 degree of body temperature. In addition, the air is humidified, and dust and other particulate matter is removed by vibrissae, short, thick hairs, present in the vestibule. The cilia of the respiratory epithelium move the particulate matter towards the pharynx where it passes into the esophagus and is digested in the stomach. The lateral wall of the nasal cavity is mainly made up by the maxilla, however there is a deficiency that is compensated by: the perpendicular plate of the palatine bone, the medial pterygoid plate, the labyrinth of the ethmoid and the inferior concha. The nasal cavity is enclosed by the nasal bone above. The floor of the nasal cavity, which forms the roof of the mouth, is made up by the bones of the hard palate: the horizontal plate of the palatine bone posteriorly and the palatine process of the maxilla anteriorly. To
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    Peritoneum

    Peritoneum

    The peritoneum ( /ˌpɛrɨtənˈiəm/) is the serous membrane that forms the lining of the abdominal cavity or the coelom—it covers most of the intra-abdominal (or coelomic) organs—in amniotes and some invertebrates (annelids, for instance). It is composed of a layer of mesothelium supported by a thin layer of connective tissue. The peritoneum both supports the abdominal organs and serves as a conduit for their blood and lymph vessels and nerves. The abdominal cavity (the space bounded by the vertebrae, abdominal muscles, diaphragm and pelvic floor) should not be confused with the intraperitoneal space (located within the abdominal cavity, but wrapped in peritoneum). The structures within the intraperitoneal space are called "intraperitoneal" (e.g. the stomach), the structures in the abdominal cavity that are located behind the intraperitoneal space are called "retroperitoneal" (e.g. the kidneys), and those structures below the intraperitoneal space are called "subperitoneal" or "infraperitoneal" (e.g. the bladder). Although they ultimately form one continuous sheet, two types or layers of peritoneum and a potential space between them are referenced: There are two main regions of the
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    Pudendal nerve

    Pudendal nerve

    The pudendal nerve is a sensory and somatic nerve in the pelvic region that innervates the external genitalia of both sexes, as well as sphincters for the bladder and the rectum. It originates in Onuf's nucleus in the sacral region of the spinal cord, and travels in the S2-S4 nerves of the sacral plexus. The pudendal nerve originates in the sacral plexus; it derives its fibers from the ventral rami of the second, third, and fourth sacral nerves (S2, S3, S4). It passes between the piriformis and coccygeus muscles and leaves the pelvis through the lower part of the greater sciatic foramen. It crosses the spine of the ischium, and reenters the pelvis through the lesser sciatic foramen. It accompanies the internal pudendal vessels upward and forward along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal. The pudendal nerve gives off the inferior rectal nerves. It soon divides into two terminal branches: the perineal nerve, and the dorsal nerve of the penis (in males) or the dorsal nerve of the clitoris (in females). Research shows that variations in pudendal nerve origin are possible. For example, the pudendal
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    Sciatic nerve

    Sciatic nerve

    The sciatic nerve (also known as the ischiadic nerve and the ischiatic nerve) is a large nerve in humans and other animals. It begins in the lower back and runs through the buttock and down the lower limb. It is the longest and widest single nerve in the human body going from the top of the leg to the foot on the posterior aspect. The sciatic supplies nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot. It is derived from spinal nerves L4 through S3. It contains fibres from both the anterior and posterior divisions of the lumbosacral plexus. The nerve gives off articular and muscular branches. The muscular branch eventually gives off the tibial nerve and common fibular nerve, which innervates the muscles of the (lower) leg. The tibial nerve goes on to innervate all muscles of the foot except the extensor digitorum brevis (which is innervated by the common fibular nerve). The sciatic nerve innervates the skin on the posterior aspect of the thigh and gluteal regions, as well as the entire lower leg (except for its medial aspect). Pain caused by a compression or irritation of the sciatic nerve by a problem in the lower back is
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    Urinary bladder

    Urinary bladder

    The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible (or elastic) organ, the bladder sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. Bladders occur throughout much of the animal kingdom, but are very diverse in form and in some cases are not homologous with the urinary bladder in humans. The human urinary bladder is derived in embryo from the urogenital sinus and, it is initially continuous with the allantois. In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the prostate, and separated from the rectum by the rectovesical excavation. In females, the bladder sits inferior to the uterus and anterior to the vagina; thus, its maximum capacity is lower than in males. It is separated from the uterus by the vesicouterine excavation. In infants and young children, the urinary bladder is in the abdomen even when empty. The detrusor muscle is a layer of the urinary bladder wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. When the bladder is stretched, this signals the
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    Bronchiole

    Bronchiole

    The bronchioles or bronchioli are the first passageways by which the air passes through the nose or mouth to the air sacs of the lungs in which branches no longer contain cartilage or glands in their submucosa. They are branches of the bronchi. The bronchioles terminate by entering the circular sacs called alveoli. A pulmonary lobule is the portion of the lung ventilated by one bronchiole. Bronchioles are approximately 1mm or less in diameter and their walls consist of ciliated cuboidal epithelium and a layer of smooth muscle. Bronchioles divide into even smaller terminal bronchioles that are 0.5mm or less in diameter. Terminal bronchioles in turn divide into respiratory bronchioles which divide into alveolar ducts. Terminal bronchioles mark the end of the conducting division of air flow in the respiratory system while respiratory bronchioles are the beginning of the respiratory division where actual gas exchange takes place. The diameter of the bronchioles plays an important role in air flow. The bronchioles change diameter to either increase or reduce air flow. An increase in diameter is called bronchodilation and is stimulated by either epinephrine or sympathetic nerves to
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    Carpus

    Carpus

    Carpus is anatomical assembly connecting the hand to forearm. In human anatomy, the main role of the carpus is to facilitate effective positioning of the hand and powerful use of the extensors and flexors of the forearm, but the mobility of individual carpal bones increase the freedom of movements at the wrist. In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers (or toes in quadrupeds), whereas those of the metacarpus do. The corresponding part of the foot is the tarsus. The carpal bones allow the wrist to move and rotate vertically. The Latin word "carpus" is derived from Greek καρπὁς meaning "wrist". The root "carp-" translates to "pluck", an action performed by the wrist. In human anatomy, the carpal bones can be classified as belonging to two transverse rows or three longitudinal columns. The pair of rows together form an arch which is convex proximally and concave distally. On the palmar side, the carpus is concave, forming the carpal tunnel which is covered by the flexor retinaculum. Because the proximal row is simultaneously related to the articular
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    Intervertebral disc

    Intervertebral disc

    Intervertebral discs (or intervertebral fibrocartilage) lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together. Discs consist of an outer annulus fibrosus, which surrounds the inner nucleus pulposus. The annulus fibrosus consists of several layers of fibrocartilage. The strong annular fibers contain the nucleus pulposus and distribute pressure evenly across the disc. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel with the consistency of jelly. The nucleus of the disc acts as a shock absorber, absorbing the impact of the body's daily activities and keeping the two vertebrae separated. The disc can be likened to a jelly doughnut: whereby the annulus fibrosis is similar to the dough and the nucleus pulposis is the jelly. If one presses down on the front of the doughnut the jelly moves posteriorly or to the back. When one develops a prolapsed disc the jelly/nucleus pulposus is forced out of the doughnut/disc and may put pressure on the nerve located near the disc. This can give one the symptoms of sciatica. There is one disc between
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    Left ventricle

    Left ventricle

    The left ventricle is one of four chambers (two atria and two ventricles) in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve. The left ventricle is shorter and more conical in shape than the right, and on transverse section its concavity presents an oval or nearly circular outline. It forms a small part of the sternocostal surface and a considerable part of the diaphragmatic surface of the heart; it also forms the apex of the heart. The left ventricle is thicker and more muscular than the right ventricle because it pumps blood at a higher pressure. By teenage and adult age, its walls have thickened to three to sixty-nine times greater than that of the right ventricle. This reflects the typical five times greater pressure workload this chamber performs while accepting blood returning from the pulmonary veins at ~80mmHg pressure (equivalent to around 11 kPa) and pushing it forward to the typical ~120mmHg pressure (around 16.3 kPa) in the aorta during each heartbeat. (The pressures stated are resting values and stated as relative to surrounding atmospheric which is the typical "0" reference
    6.33
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    144
    Eardrum

    Eardrum

    The eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in air to vibration in fluid. The malleus bone bridges the gap between the eardrum and the other ossicles. There are two general regions of the tympanic membrane: the pars flaccida (upper region, see picture on right) and the pars tensa. The pars flaccida consists of two layers, is relatively fragile, and is associated with eustachian tube dysfunction and cholesteatomas. The larger pars tensa region consists of three layers: skin, fibrous tissue, and mucosa. It is comparatively robust, and is the region most commonly associated with perforations. Rupture or perforation of the eardrum can lead to conductive hearing loss. Collapse or retraction of the eardrum can also cause conductive hearing loss or even cholesteatoma. The Bajau people of the Pacific intentionally rupture their eardrums at an early age in order to facilitate diving and
    8.00
    1 votes
    145
    Fibula

    Fibula

    The fibula (/ˈfɪbjələ/) or calf bone is a leg bone located on the lateral side of the tibia, with which it is connected above and below. It is the smaller of the two bones, and, in proportion to its length, the most slender of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the level of the knee joint, and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia, and forms the lateral part of the ankle joint. The word fibula can be dated back to c. 1670 to describe a clasp or brooch, and was first used in English for the smaller bone in the lower leg c. 1706. It derives from Latin fībula, also meaning a clasp or brooch. The bone was so called because it resembles a clasp like a modern safety pin. The bone has the following components: The blood supply is important for planning free tissue transfer because the fibula is commonly used to reconstruct the mandible. The shaft is supplied in its middle third by a large nutrient vessel from the fibular artery. It is also perfused from its periosteum which receives
    8.00
    1 votes
    146
    Pronator quadratus

    Pronator quadratus

    Pronator quadratus is a square shaped muscle on the distal forearm that acts to pronate (turn so the palm faces downwards) the hand. As it is on the anterior side of the arm, it is innervated by a branch of the median nerve, the anterior interosseous nerve (roots C8 and T1 with T1 being primary). Arterial blood comes via the interosseous artery. Its fibers run perpendicular to the direction of the arm, running from the most distal quarter of the anterior ulna to the distal quarter of the anterior radius. It is the only muscle that attaches only to the ulna at one end and the radius at the other end. When pronator quadratus contracts, it pulls the lateral side of the radius towards the ulna, thus pronating the hand. Its deep fibers serve to keep the two bones in the forearm bound together. It also aids in wrist extension.
    8.00
    1 votes
    147
    Xiphoid process

    Xiphoid process

    The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process (extension) of the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major joints, this is non-movable. Much the way the first seven ribs articulate with the sternum, the cartilage in the celiac plexus joins on the xiphoid process, reinforcing it, and indirectly attaches the costal cartilage to the sternum. In newborn babies and young (especially slender) infants, the tip of the xiphoid process may be both seen and felt as a lump just below the sternal notch. The xiphoid process is considered to be at the level of the 9th thoracic vertebra and the T6 dermatome. The xiphoid process can be naturally bifurcated, and sometimes perforated. These variances in morphology are inheritable, which can help group family members together when dealing with burial remains. These morphological differences pose no health risk, and are simply a difference in form. Pressure on the xiphoid process should be avoided when administering chest compressions in CPR, as this
    8.00
    1 votes
    148
    Brachioradialis

    Brachioradialis

    Brachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by way of the brachioradialis tendon, and to the lateral supracondylar ridge of the humerus. Brachioradialis flexes the forearm at the elbow. When the forearm is pronated, the brachioradialis tends to supinate as it flexes. In a supinated position, it tends to pronate as it flexes. The brachioradialis is a stronger elbow flexor when the forearm is in a midposition between supination and pronation at the radioulnar joint. When pronated, the brachioradialis is more active during elbow flexion since the biceps brachii is in a mechanical disadvantage. With the insertion of the muscle so far from the fulcrum of the elbow, the brachioradialis does not generate as much force as the brachialis or the biceps. It is effective mainly when those muscles have already partially flexed at the elbow. The brachioradialis flexes the forearm at the elbow, especially when quick movement is required and when a weight is lifted during slow flexion of the forearm. The
    5.25
    4 votes
    149
    Pia mater

    Pia mater

    Pia mater ( /ˈpaɪ.ə ˈmeɪtər/ or  /ˈpiː.ə ˈmɑːtər/) often referred to as simply the pia, is the delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord. The word finds its roots in Latin, meaning literally "tender mother." The other two meningeal membranes are the dura mater and the arachnoid mater. Pia mater is a thin fibrous tissue that is impermeable to fluid. This allows the pia mater to enclose cerebrospinal fluid. By containing this fluid the pia mater works with the other meningeal layers to protect and cushion the brain. The pia mater allows blood vessels to pass through and nourish the brain. The perivascular space created between blood vessels and pia mater functions as a lymphatic system for the brain. When the pia mater becomes irritated and inflamed the result is meningitis. Pia mater is the thin, translucent, mesh-like meningeal envelope, spanning nearly the entire surface of the brain. It is only absent at the natural openings between the ventricles, the foramen of Majendie and the foramina of Luschka. The pia is firmly adhered to the surface of the brain and loosely connected to the arachnoid layer. Because of this continuum, the
    5.25
    4 votes
    150
    Suboccipital nerve

    Suboccipital nerve

    The suboccipital nerve is the dorsal primary ramus of the first cervical nerve (C1). It exits the spinal cord between the skull and the first cervical vertebra, the atlas. It lies within the suboccipital triangle along with the vertebral artery, where the artery enters the foramen magnum. It supplies muscles of the suboccipital triangle, the rectus capitis posterior major, obliquus capitis superior, and obliquus capitis inferior. The suboccipital nerve also innervates rectus capitis posterior minor.
    5.25
    4 votes
    151
    Brachialis muscle

    Brachialis muscle

    The brachialis (brachialis anticus) is a muscle in the upper arm that flexes the elbow joint. It lies deeper than the biceps brachii, and is a synergist that assists the biceps brachii in flexing at the elbow. It makes up part of the floor of the region known as the cubital fossa. The brachialis originates from the lower half of the front of the humerus, near the insertion of the deltoid muscle, which it embraces by two angular processes. Its origin extends below to within 2.5 cm of the margin of the articular surface of the humerus at the elbow joint. It also arises from the intermuscular septa of the arm, but more extensively from the medial than the lateral; it is separated from the lateral below by the brachioradialis and extensor carpi radialis longus muscles. Its fibers converge to a thick tendon, which is inserted into the tuberosity of the ulna and the rough depression on the anterior surface of the coronoid process of the ulna. The brachialis muscle is innervated by the musculocutaneous nerve, which runs on its superficial surface, between it and the biceps brachii. Part of it is also innervated by the radial nerve (proprioceptive branch) which allows it to be split during
    7.00
    2 votes
    152
    Metatarsus

    Metatarsus

    The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side (side of great toe): the first, second, third, fourth, and fifth metatarsal. The metatarsals are analogous to the metacarpal bones of the hand. The five metatarsals are dorsally convex long bones consisting of a shaft or body, a base, and a head. The body is prismoid in form, tapers gradually from the tarsal to the phalangeal extremity, and is curved longitudinally, so as to be concave below, slightly convex above. The base or posterior extremity is wedge-shaped, articulating proximally with the tarsal bones, and by its sides with the contiguous metatarsal bones: its dorsal and plantar surfaces are rough for the attachment of ligaments. The head or anterior extremity presents a convex articular surface, oblong from above downward, and extending farther backward below than above. Its sides are flattened, and on each is a depression, surmounted by a tubercle, for ligamentous attachment. Its plantar surface is grooved antero-posteriorly
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    153
    Nasopharynx

    Nasopharynx

    The nasopharynx (nasal part of the pharynx) is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent (open). In front it communicates through the choanae with the nasal cavities. On its lateral wall is the pharyngeal ostium of the auditory tube, somewhat triangular in shape, and bounded behind by a firm prominence, the torus tubarius or cushion, caused by the medial end of the cartilage of the tube which elevates the mucous membrane. Two folds arise from the cartilaginous opening: Behind the ostium of the auditory tube is a deep recess, the pharyngeal recess (fossa of Rosenmüller). On the posterior wall is a prominence, best marked in childhood, produced by a mass of lymphoid tissue, which is known as the pharyngeal tonsil. Above the pharyngeal tonsil, in the middle line, an irregular flask-shaped depression of the mucous membrane sometimes extends up as far as the basilar process of the occipital bone; it is known as the pharyngeal bursa. This article was originally based on an entry from a public domain edition of Gray's
    7.00
    2 votes
    154
    Nucleus accumbens

    Nucleus accumbens

    The nucleus accumbens (NAcc), also known as the accumbens nucleus or as the nucleus accumbens septi (Latin for nucleus leaning against the septum or as The pleasure center)), is a collection of neurons and forms the main part of the ventral striatum. It is thought to play an important role in reward, pleasure, laughter, addiction, aggression, fear, and the placebo effect. Each half of the brain has one nucleus accumbens. It is located where the head of the caudate and the anterior portion of the putamen meet just lateral to the septum pellucidum. The nucleus accumbens and the olfactory tubercle collectively form the ventral striatum, which is part of the basal ganglia. The nucleus accumbens can be divided into two structures—the nucleus accumbens core and the nucleus accumbens shell. These structures have different morphology and function. The principal neuronal cell type found in the nucleus accumbens is the medium spiny neuron. The neurotransmitter produced by these neurons is gamma-aminobutyric acid (GABA), one of the main inhibitory neurotransmitters of the central nervous system. These neurons are also the main projection or output neurons of the nucleus accumbens. While 95%
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    155
    Pericardium

    Pericardium

    The pericardium (from the Greek περι, "around" and κάρδιον, "heart" /perikardion/) is a double-walled sac containing the heart and the roots of the great vessels. Pericardium is a tough double layered membrane which covers the heart. The space between the two layers of it is filled with a pericardium fluid which protects the heart from any kind of external jerk or shock. There are two layers to the pericardial sac: the outermost fibrous pericardium and the inner serous pericardium. The serous pericardium, in turn, is divided into two layers, the parietal pericardium, which is fused to and inseparable from the fibrous pericardium, and the visceral pericardium, which is part of the epicardium. The epicardium is the layer immediately outside of the heart muscle proper (the myocardium). The visceral layer extends to the beginning of the great vessels, becoming one with the parietal layer of the serous pericardium. This happens at two areas; where the aorta and pulmonary trunk leave the heart and where the superior vena cava, inferior vena cava and pulmonary veins enter the heart. In between the parietal and visceral pericardial layers there is a potential space called the pericardial
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    2 votes
    156
    Rhinencephalon

    Rhinencephalon

    In animal anatomy, the rhinencephalon is a part of the brain involved with olfaction. The term rhinencephalon has been used to describe different structures at different points in time. One definition includes the olfactory bulb, olfactory tract, anterior olfactory nucleus, anterior perforated substance, medial olfactory stria, lateral olfactory stria, parts of the amygdala and prepyriform area. Some references classify other areas of the brain related to perception of smell as rhinencephalon, but areas of the human brain that receive fibers strictly from the olfactory bulb are limited to those of the paleopallium. As such, the rhinencephalon includes the olfactory bulb, the olfactory tract, the olfactory tubercle and striae, the anterior olfactory nucleus and parts of the amygdala and the piriform cortex.
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    2 votes
    157
    Sternocleidomastoid muscle

    Sternocleidomastoid muscle

    In human anatomy, the sternocleidomastoid muscle ( /ˌstɜrnɵˌkliːdɵˈmæstɔɪd/), also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck. When acting together it flexes the neck and extends the head. When acting alone it rotates to the opposite side (contralaterally) and slightly (laterally) flexes to the same side. It also acts as an accessory muscle of inspiration, along with the scalene muscles of the neck. It is given the name sternocleidomastoid because it originates at the manubrium of the sternum (sterno-) and the clavicle (cleido-), and has an insertion at the mastoid process of the temporal bone of the skull. The sternocleidomastoid passes obliquely across the side of the neck. It is thick and narrow at its central part, but broader and thinner at either end. The two heads are separated from one another at their origins by a triangular interval (supraclavicular fossa) but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin
    7.00
    2 votes
    158
    Broca's area

    Broca's area

    Broca's area is a region of the hominid brain with functions linked to speech production. The production of language has been linked to the Broca's area since Pierre Paul Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal gyrus of the brain. Since then, the approximate region he identified has become known as Broca's area, and the deficit in language production as Broca's aphasia. Broca's area is now typically defined in terms of the pars opercularis and pars triangularis of the inferior frontal gyrus, represented in Brodmann's cytoarchitectonic map as areas 44 and 45 of the dominant hemisphere. Studies of chronic aphasia have implicated an essential role of Broca's area in various speech and language functions. Further, functional MRI studies have also identified activation patterns in Broca's area associated with various language tasks. However, slow destruction of the Broca's area by brain tumors can leave speech relatively intact suggesting its functions can shift to nearby areas in the brain. Broca's area is often identified by visual inspection of the topography of the brain either by macrostructural
    6.00
    3 votes
    159
    Chorion

    Chorion

    The chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes. The chorionic villi emerge from the chorion, invade the endometrium, and allow transfer of nutrients from maternal blood to fetal blood. The chorion consists of two layers: an outer formed by the trophoblast, and an inner formed by the somatic mesoderm; the amnion is in contact with the latter. The trophoblast is made up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer of Langhans, and an external layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblast. The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo. The chorionic villi are at first small and non-vascular, and consist of the trophoblast only, but they increase in size and ramify, whereas the mesoderm, carrying branches of the umbilical vessels, grows into them, and, in this
    6.00
    3 votes
    160
    Coracoid

    Coracoid

    The coracoid process (from Greek κόραξ, crow) is a small hook-like structure on the lateral edge of the superior anterior portion of the scapula. Pointing laterally forward, it, together with the acromion, serves to stabilize the shoulder joint. It is palpable in the deltopectoral groove between the deltoid and pectoralis major muscles. "Coracoid" in itself means "like a raven's beak", with reference to its shape. (Greek "Korax" = Raven) It is the site of attachment for several structures: The coracoid process is a thick curved process attached by a broad base to the upper part of the neck of the scapula; it runs at first upward and medialward; then, becoming smaller, it changes its direction, and projects forward and lateralward. The ascending portion, flattened from before backward, presents in front a smooth concave surface, across which the Subscapularis passes. The horizontal portion is flattened from above downward; its upper surface is convex and irregular, and gives attachment to the Pectoralis minor; its under surface is smooth; its medial and lateral borders are rough; the former gives attachment to the Pectoralis minor and the latter to the coracoacromial ligament; the
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    161
    Ectoderm

    Ectoderm

    Ectoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the mesoderm (middle layer) and endoderm (most proximal layer), with the ectoderm as the most exterior (or distal) layer. It emerges first and forms from the outer layer of germ cells. Generally speaking, the ectoderm differentiates to form the nervous system (spine, peripheral nerves and brain), tooth enamel and the epidermis (the outer part of integument). It also forms the lining of mouth, anus, nostrils, sweat glands, hair and nails. In vertebrates, the ectoderm has three parts: external ectoderm (also known as surface ectoderm), the neural crest, and neural tube. The latter two are known as neuroectoderm.
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    162
    Pharynx

    Pharynx

    The human pharynx (plural: pharynges) is the part of the throat situated immediately inferior to (below) the mouth and nasal cavity, and superior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx (epipharynx), the oropharynx (mesopharynx), and the laryngopharynx (hypopharynx). The pharynx is part of the digestive system and also the respiratory system; it is also important in vocalization. The most cephalad portion of the pharynx. It extends from the base of the skull to the upper surface of the soft palate. It includes the space between the internal nares and the soft palate and lies superior to the oral cavity. The pharyngeal tonsils, more commonly referred to as the adenoids, are lymphoid tissue structures located in the posterior wall of the nasopharynx. Polyps or mucus can obstruct the nasopharynx, as can congestion due to an upper respiratory infection. The Eustachian tubes, which connect the middle ear to the pharynx, open into the nasopharynx. The opening and closing of the Eustachian tubes serves to equalize the barometric pressure in the middle ear with that of the ambient atmosphere. The anterior aspect of the
    6.00
    3 votes
    163
    Trigeminal nerve

    Trigeminal nerve

    The trigeminal nerve (the fifth cranial nerve, also called the fifth nerve, or simply CNV or CN5) is a nerve responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. It is the largest of the cranial nerves. Its name ("trigeminal" = tri- or three, and -geminus or twin, or thrice twinned) derives from the fact that each trigeminal nerve, one on each side of the pons, has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has both sensory and motor functions. Sensory information from the face and body is processed by parallel pathways in the central nervous system. The motor division of the trigeminal nerve is derived from the basal plate of the embryonic pons, while the sensory division originates from the cranial neural crest. The sensory function of the trigeminal nerve is to provide the tactile, proprioceptive, and nociceptive afference of the face and mouth. The motor function activates the muscles of mastication, the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the
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    3 votes
    164
    Loop of Henle

    Loop of Henle

    In the kidney, the loop of Henle (or Henle's loop or ansa nephroni) is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer F. G. J. Henle, the loop of Henle's main function is to create a concentration gradient in the medulla of the kidney. By means of a countercurrent multiplier system, which utilizes electrolyte pumps, the loop of Henle creates an area of high urine concentration deep in the medulla, near the collecting duct. Water present in the filtrate in the collecting duct flows through aquaporin channels out of the collecting duct, moving passively down its concentration gradient. This process reabsorbs water and creates a concentrated urine for excretion. It can be divided into five parts: The loop of Henle is supplied by blood in a series of straight capillaries descending from the cortical efferent arterioles. These capillaries (called the vasa recta; recta is from the Latin for "straight") also have a countercurrent multiplier mechanism that prevents washout of solutes from the medulla, thereby maintaining the medullary concentration. As water is osmotically driven from the descending limb
    5.67
    3 votes
    165
    Oocyte

    Oocyte

    An oocyte (UK: /ˈəʊəsʌɪt/, US: /ˈoʊ.oʊ.saɪt/), ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC) which undergoes mitosis to form an oogonium. During oogenesis the oogonium becomes a primary oocyte. The formation of an oocyte is called oocytogenesis, which is a part of oogenesis. Oogenesis results in the formation of both primary oocytes before birth, and of secondary oocytes after it as part of ovulation. Oocytes are rich in cytoplasm which contains yolk granules to nourish the cell early in development. During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle. The only normal human type of secondary oocyte has the 23rd (sex) chromosome as 23,X (female-determining), whereas sperm can have 23,X (female-determining) or 23,Y (male-determining). The space wherein an ovum or immature ovum is located is the cell-nest. Because the fate of an oocyte is to become fertilized and ultimately grow into a fully functioning organism, it must be ready to
    5.67
    3 votes
    166
    Palatine bone

    Palatine bone

    The palatine bone (/ˈpælətaɪn/) is a bone in many species of the animal kingdom, commonly termed the palatum (Latin palatum; unrelated to palatium 'palace', from which other senses of palatine derive). It is situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid. It contributes to the walls of three cavities: the floor and lateral wall of the nasal cavity, the roof of the mouth, and the floor of the orbit; it enters into the formation of two fossæ, the pterygopalatine and pterygoid fossæ; and one fissure, the inferior orbital fissure. The palatine bone somewhat resembles the letter L, and consists of a Horizontal plate of palatine bone and a Perpendicular plate of palatine bone and three outstanding processes—viz., the Pyramidal process of palatine bone, which is directed backward and lateralward from the junction of the two parts, and the Orbital process of palatine bone and Sphenoidal process of palatine bone, which surmount the vertical part, and are separated by a deep notch, the sphenopalatine notch. The human palatine articulates with six bones: the sphenoid, ethmoid, maxilla, inferior nasal concha, vomer and opposite
    5.67
    3 votes
    167
    Radial nerve

    Radial nerve

    The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin. It originates from the posterior cord of the brachial plexus, carrying fibers from the ventral roots of spinal nerves C5, C6, C7, C8 & T1. The radial nerve and its branches provide motor innervation to the dorsal arm muscles (the triceps brachii and the anconeus) and the extrinsic extensors of the wrists and hands; it also provides cutaneous sensory innervation to most of the back of the hand. The ulnar nerve provides cutaneous sensory innervation to the back of the little finger and adjacent half of the ring finger. The radial nerve divides into a deep branch, which becomes the posterior interosseous nerve, and a superficial branch, which goes on to innervate the dorsum (back) of the hand. The radial nerve originates as a terminal branch of the posterior cord of the brachial plexus. It goes through the arm, first in the posterior compartment of the arm, and later in the anterior compartment of the
    5.67
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    168
    Axis

    Axis

    In anatomy, the second cervical vertebra (C2) of the spine is named the axis (from Latin axis, "axle") or epistropheus. It forms the pivot upon which the first cervical vertebra (the atlas), which carries the head, rotates. The most distinctive characteristic of this bone is the strong odontoid process ("dens") which rises perpendicularly from the upper surface of the body. That peculiar feature gives to the vertebra a rarely used third name: vertebra dentata. It is the bone responsible for death in Judicial Hanging as the odontoid process usually breaks and hits the medulla oblongata, damaging the vital centres. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra. It presents in front a median longitudinal ridge, separating two lateral depressions for the attachment of the Longus colli muscles. Its under surface is concave from before backward and convex from side to side. The dens, or odontoid process, exhibits a slight constriction or neck where it joins the body. The pedicles are broad and strong, especially in front, where they coalesce with the sides of the body and the root of the odontoid
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    169
    Brain stem

    Brain stem

    In vertebrate anatomy the brainstem (or brain stem) is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. It is usually described as including the medulla oblongata (myelencephalon), pons (part of metencephalon), and midbrain (mesencephalon). Less frequently, parts of the diencephalon are included. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves. Though small, this is an extremely important part of the brain as the nerve connections of the motor and sensory systems from the main part of the brain to the rest of the body pass through the brain stem. This includes the corticospinal tract (motor), the posterior column-medial lemniscus pathway (fine touch, vibration sensation and proprioception) and the spinothalamic tract (pain, temperature, itch and crude touch). The brain stem also plays an important role in the regulation of cardiac and respiratory function. It also regulates the central nervous system, and is pivotal in maintaining consciousness and regulating the sleep cycle. The brain stem has many basic functions including heart rate, breathing, sleeping and eating. 1. Conduit
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    2 votes
    170
    Brodmann area 40

    Brodmann area 40

    Brodmann area 40, or BA40, is part of the parietal cortex in the human brain. The inferior part of BA40 is in the area of the supramarginal gyrus, which lies at the posterior end of the lateral fissure, in the inferior lateral part of the parietal lobe. It is bounded approximately by the intraparietal sulcus, the inferior postcentral sulcus, the posterior subcentral sulcus and the lateral sulcus. Cytoarchitecturally it is bounded caudally by the angular area 39 (H), rostrally and dorsally by the caudal postcentral area 2, and ventrally by the subcentral area 43 and the superior temporal area 22 (Brodmann-1909). Cytoarchitectonically defined subregions of rostral BA40/the supramarginal gyrus are PF, PFcm, PFm, PFop, and PFt. Area PF is the homologue to macaque area PF, part of the mirror neuron system, and active in humans during imitation. The supramarginal gyrus part of Brodmann area 40 is the region in the inferior parietal lobe that is involved in reading both in regards to meaning and phonology.
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    171
    Corpus callosum

    Corpus callosum

    The corpus callosum (Latin: tough body), also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication. It is the largest white matter structure in the brain, consisting of 200–250 million contralateral axonal projections. The posterior portion of the corpus callosum is called the splenium; the anterior is called the genu (or "knee"); between the two is the truncus, or "body", of the corpus callosum. The part between the body and the splenium is often markedly thinned and thus referred to as the "isthmus". The rostrum is the part of the corpus callosum that projects posteriorly and inferiorly from the anteriormost genu, as can be seen on the sagittal image of the brain displayed on the right. The rostrum is so named for its resemblance to a bird's beak. Thinner axons in the genu connect the prefrontal cortex between the two halves of the brain. Thicker axons in the midbody of the corpus callosum and in the splenium interconnect areas of the premotor and supplementary motor regions and motor cortex,
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    172
    Maxilla

    Maxilla

    The maxilla (/mækˈsɪlə/; plural: maxillae /mækˈsɪliː/) is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible (lower jaw), which is also a fusion of two halves at the mandibular symphysis. Sometimes (e.g. in bony fish), the maxilla is called "upper maxilla," with the mandible being the "lower maxilla." Conversely, in birds the upper jaw is often called "upper mandible." The alveolar process of the maxilla holds the upper teeth, and is referred to as the maxillary arch. The maxilla attaches laterally to the zygomatic bones (cheek bones). The maxilla assists in forming the boundaries of three cavities: The maxilla also enters into the formation of two fossae: the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. Each half of the fused maxilla consists of: The maxilla articulates with nine bones: Sometimes it articulates with the orbital surface, and sometimes with the lateral pterygoid plate of the sphenoid. In most vertebrates, the foremost part of the upper jaw, to which the incisors are attached in mammals consists of a separate pair of bones, the premaxillae. These fuse with the
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    173
    Orbit

    Orbit

    In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is 30 ml, of which the eye occupies 6.5 ml. The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and point back into the head. Each consists of a base, an apex and four walls. They protect the eye from mechanical injury. The base, which opens in the face, has four borders. The following bones take part in their formation: The apex lies near the medial end of superior orbital fissure and contains the optic canal (containing the optic nerve and ophthalmic artery), which communicates with middle cranial fossa. The roof (superior wall) is formed primarily by the orbital plate frontal bone, and also the lesser wing of sphenoid near the apex of the orbit. The orbital surface presents medially by trochlear fovea and laterally by lacrimal fossa. The floor (inferior wall) is formed by the orbital surface of maxilla, the orbital surface of zygomatic bone and the minute orbital process of palatine bone. Medially,
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    174
    Aortic valve

    Aortic valve

    The aortic valve is one of the valves of the heart. It is normally tricuspid (with three leaflets), although in 1% of the population it is found to be congenitally bicuspid (two leaflets). It lies between the left ventricle and the aorta. During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound (S2). There are two protypical processes that can affect the aortic valve - aortic stenosis in which the valve fails to open fully, thereby obstructing blood flow out from the heart, and aortic insufficiency, also called aortic regurgitation, in which the aortic valve is incompetent and blood flows passively back to the heart in the wrong direction. These two conditions frequently co-exist. The most common congenital abnormality of the heart is the bicuspid
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    3 votes
    175
    Femoral triangle

    Femoral triangle

    The femoral triangle (of Scarpa) is an anatomical region of the upper inner human thigh. It is bounded by: Its floor is formed by the pectineus and adductor longus muscles medially and iliopsoas muscle laterally. Its roof is formed by the fascia lata, except at the saphenous opening where it is formed by the cribriform fascia. The femoral triangle is shaped like the sail of a sailing ship. Its boundaries can be remembered using the mnemonic, "SAIL" for Sartorius, Adductor longus and Inguinal Ligament. It is important as a number of vital structures pass through it, right under the skin. The following structures are contained within the femoral triangle (from lateral to medial): 1) Terminal part of the femoral nerve and its branches; the femoral branch of genitofemoral nerve, which innervates the skin covering the roof of the femoral triangle; and the Lateral cutaneous nerve of thigh, which later divides into anterior and posterior branches. 2) The three compartments of the femoral sheath (From lateral to medial): Since the femoral triangle provides easy access to a major artery, coronary angioplasty and peripheral angioplasty is often performed by entering the femoral artery at
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    176
    Amnion

    Amnion

    The amnion is a membrane building the amniotic sac that surrounds and protects an embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota”; but not in amphibians and fish (Ichthyopsida), which are consequently termed “Anamniota”. The primary role of this is the protection of the embryo for its development. It stems from the extraembryonic somatic mesoderm on the outer side and the extraembryonic ectoderm on the inner side. In the human embryo, the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac, and appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk—the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion. When first formed, the amnion is in contact
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    177
    Hamate bone

    Hamate bone

    The hamate bone (unciform bone) is a bone in the human wrist readily distinguishable by its wedge shape and a hook-like process projecting from its volar surface. It is situated at the medial and lower angle of the carpus, with its base downward, resting on the fourth and fifth metacarpal bones, and its apex directed upward and lateralward. The bone is also found in many other mammals, and is homologous with the "fourth distal carpal" of reptiles and amphibians. The etymology derives from the Latin hamatus "hooked," from hamus which means "hook." The hamate bone has six surfaces: This is the bone most commonly fractured when an amateur golfer hits the ground hard with a golf club on the downswing. The fracture is usually a hairline fracture, commonly missed on normal X-Rays. Symptoms are pain aggravated by gripping, tenderness over the hamate and symptoms of irritation of the ulnar nerve. This is characterized by numbness and weakness of the pinky finger with partial involvement of the ring finger as well, the "ulnar 1½ fingers." It is also a common injury in baseball players. Several professional baseball players have had the bone removed during the course of their careers. This
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    178
    Labyrinth

    Labyrinth

    The labyrinth is a system of fluid passages in the inner ear, including both the cochlea, which is part of the auditory system, and the vestibular system, which provides the sense of balance. It is named by analogy with the mythical maze that imprisoned the Minotaur, because of its appearance. The bony labyrinth, or osseous labyrinth, is the network of passages with bony walls lined with periosteum. The bony labyrinth is lined with the membranous labyrinth. There is a layer of perilymph between them. The three parts of the bony labyrinth are the vestibule of the ear, the semicircular canals, and the cochlea. The vestibular system is the region of the inner ear where the semicircular canals converge, close to the cochlea (the hearing organ). The vestibular system works with the visual system to keep objects in focus when the head is moving. Joint and muscle receptors also are important in maintaining balance. The brain receives, interprets, and processes the information from these systems that control our balance. Interference with or infection of the labyrinth can result in a syndrome of ailments called Labyrinthitis. The symptoms of Labyrinthitis include temporary nausea,
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    179
    Ligamentum arteriosum

    Ligamentum arteriosum

    The ligamentum arteriosum (or arterial ligament) is a small ligament attached to the superior surface of the pulmonary trunk and the inferior surface of the aortic arch. It is a nonfunctional vestige of the ductus arteriosus, and is formed within three weeks of birth. The ligamentum arteriosum is closely related to the left recurrent laryngeal nerve, a branch of the left vagus nerve. After splitting from the left vagus nerve, the left recurrent laryngeal loops around the aortic arch posterior to the ligamentum arteriosum, after which it ascends to the larynx. This ligament also plays a role in major trauma; it fixes the aorta in place during rapid decelerations recoil, consequently potentially resulting in ruptured aorta.
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    180
    Occipital bone

    Occipital bone

    The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal. The foramen magnum (Latin for large hole) is a large oval aperture with its long diameter antero-posterior; it is wider behind than in front where it is encroached upon by the condyles. It transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the membrana tectoria and alar ligaments. The superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. The inferior angle is fused with the body of the sphenoid. The lateral angles are situated at the extremities of the grooves for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal and the mastoid part of the temporal. The superior borders extend from the superior to the lateral angles: they are deeply serrated
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    181
    Scrotum

    Scrotum

    In some male mammals, the scrotum is a dual-chambered protuberance of skin and muscle, containing the testicles and divided by a septum. It is an extension of the perineum, and is located between the penis and anus. In humans and some other mammals, the scrotum becomes covered with pubic hairs at puberty. The scrotum is homologous to the labia majora in females. The scrotum may be informally or colloquially referred to as the ballsack or ballbag. The function of the scrotum appears to be to keep the temperature of the testes slightly lower than that of the rest of the body. For human beings, the scrotum temperature should be about 35-36 degrees Celsius (95-96.8 degrees Fahrenheit) , i.e. one to two degrees Celsius below the accepted normal body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit). Higher temperatures may be damaging to sperm count. The temperature is controlled by the scrotum moving the testicles closer to the abdomen when the ambient temperature is cold, and farther away when it is hot. Moving the testes away from the abdomen and increasing the exposed surface area allow a faster dispersion of excess heat. This is done by means of contraction and relaxation
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    182
    Vertebral subluxation

    Vertebral subluxation

    Vertebral subluxation is a term that is commonly used by some chiropractors (specifically, "straight chiropractors") to describe signs and symptoms of the spinal column. Those chiropractors who assert this concept also add a visceral component to the definition. Chiropractors maintain that a vertebral subluxation complex is a dysfunctional biomechanical spinal segment which is fixated. Chiropractors additionally assert that the dysfunction actively alters neurological function, which in turn, is believed to lead to neuromusculoskeletal and visceral disorders. The WHO acknowledges this difference between the medical and chiropractic definitions of a subluxation. Medical doctors only refer to "significant structural displacements" as subluxations, whereas chiropractors suggest that a dysfunctional segment, whether displaced significantly or not, should be referred to as a subluxation. This difference has been noted in the proceedings of the chiropractic profession's Mercy Center Consensus Conference: "The chiropractic profession refers to this concept as a 'subluxation'. This use of the word subluxation should not be confused with the term's precise anatomic usage which considers
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    183
    McBurney's point

    McBurney's point

    McBurney's point is the name given to the point over the right side of the abdomen that is one-third of the distance from the anterior superior iliac spine to the navel. This point roughly corresponds to the most common location of the base of the appendix where it is attached to the cecum. Deep tenderness at McBurney's point, known as McBurney's sign, is a sign of acute appendicitis. The clinical sign of referred pain in the epigastrium when pressure is applied is also known as Aaron's sign. Specific localization of tenderness to McBurney's point indicates that inflammation is no longer limited to the lumen of the bowel (which localizes pain poorly), and is irritating the lining of the peritoneum at the place where the peritoneum comes into contact with the appendix. Tenderness at McBurney's point suggests the evolution of acute appendicitis to a later stage, and thus, the increased likelihood of rupture. Other abdominal processes can also sometimes cause tenderness at McBurney's point. Thus, this sign is highly useful but neither necessary nor sufficient to make a diagnosis of acute appendicitis. Also, the anatomical position of the appendix is highly variable (for example in
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    184
    Ureter

    Ureter

    In human anatomy, the ureters are tubes made of smooth muscle fibers that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually 25–30 cm (10–12 in) long and ~3-4 mm in diameter. In humans, the ureters arise from the renal pelvis on the medial aspect of each kidney before descending towards the bladder on the front of the psoas major muscle. The ureters cross the pelvic brim near the bifurcation of the iliac arteries (which they cross anteriorly). This is a common site for the impaction of kidney stones (the others being the ureterovesical valve, where the ureter meets the bladder, and the pelvouteric junction, where the renal pelvis meets the ureter in the renal hilum). The ureters run posteroinferiorly on the lateral walls of the pelvis and then curve anteriormedially to enter the bladder through the back, at the vesicoureteric junction, running within the wall of the bladder for a few centimetres. The backflow of urine is prevented by valves known as ureterovesical valves. In females, the ureters pass through the mesometrium and under the uterine arteries on the way to the urinary bladder. An effective phrase for remembering this anatomical
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    185
    Ileum

    Ileum

    The ileum /ˈɪliːəm/ is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum. The ileum follows the duodenum and jejunum and is separated from the cecum by the ileocecal valve (ICV). In humans, the ileum is about 2–4 m long, and the pH is usually between 7 and 8 (neutral or slightly alkaline). The function of the ileum is mainly to absorb vitamin B12 and bile salts and whatever products of digestion that were not absorbed by the jejunum. The wall itself is made up of folds, each of which has many tiny finger-like projections known as villi on its surface. In turn, the epithelial cells that line these villi possess even larger numbers of microvilli. Therefore the ileum has an extremely large surface area both for the adsorption (attachment) of enzyme molecules and for the absorption of products of digestion. The DNES (diffuse neuroendocrine system) cells of the ileum secrete various hormones (gastrin, secretin, cholecystokinin) into the blood. Cells in the lining of the ileum secrete
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    186
    Brodmann area

    Brodmann area

    A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells. Brodmann areas were originally defined and numbered by the German anatomist Korbinian Brodmann based on the cytoarchitectural organization of neurons he observed in the cerebral cortex using the Nissl stain. Brodmann published his maps of cortical areas in humans, monkeys, and other species in 1909, along with many other findings and observations regarding the general cell types and laminar organization of the mammalian cortex. (The same Brodmann area number in different species does not necessarily indicate homologous areas.) A similar, but more detailed cortical map was published by Constantin von Economo and Georg N. Koskinas in 1925. Brodmann areas have been discussed, debated, refined, and renamed exhaustively for nearly a century and remain the most widely known and frequently cited cytoarchitectural organization of the human cortex. Many of the areas Brodmann defined based solely on their neuronal organization have since been correlated closely to diverse cortical functions. For example, Brodmann areas 1, 2 and 3 are the primary somatosensory
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    187
    Cingulate cortex

    Cingulate cortex

    The cingulate cortex is a part of the brain situated in the medial aspect of the cortex. It includes the cortex of the cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cingulate sulcus. The cingulate cortex is usually considered part of the limbic lobe. It receives inputs from the thalamus and the neocortex, and projects to the entorhinal cortex via the cingulum. It is an integral part of the limbic system, which is involved with emotion formation and processing, learning, and memory. The combination of these three functions makes the cingulate gyrus highly influential in linking behavioral outcomes to motivation (e.g. a certain action induced a positive emotional response, which results in learning). This role makes the cingulate cortex highly important in disorders such as depression and schizophrenia. It also plays a role in executive function and respiratory control. Cingulum means belt in Latin. The name was likely chosen because this cortex, in great part, surrounds the corpus callosum. Cingulate is an adjective (cingularis or cingulatus). The cingulate cortex is a part of the "grand lobe limbique" of Broca (1898) that
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    188
    Extensor carpi radialis longus muscle

    Extensor carpi radialis longus muscle

    Extensor carpi radialis longus is one of the five main muscles that control movements at the wrist. This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the second metacarpal bone (metacarpal of the index finger). As the name suggests, this muscle is an extensor at the wrist joint and travels along the radial side of the arm, so will also abduct (radial abduction) the hand at the wrist. That is, it manipulates the wrist so as to move the hand towards the thumb (i.e., abduction—away from the mid-position of the hand) and away from the palmar side (i.e., extension—increased angle between the palm and the front of the forearm). It originates from the lateral supracondylar ridge of the humerus, from the lateral intermuscular septum, and by a few fibers from the lateral epicondyle of the humerus. The fibres end at the upper third of the forearm in a flat tendon, which runs along the lateral border of the radius, beneath the Abductor pollicis longus and Extensor pollicis brevis; it then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the Extensor carpi radialis brevis,
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    189
    Vagus nerve

    Vagus nerve

    The vagus nerve ( /ˈveɪɡəs/ VAY-gəs), also called pneumogastric nerve or cranial nerve X, is the tenth of twelve (excluding CN0) paired cranial nerves. Upon leaving the medulla between the medullary pyramid and the inferior cerebellar peduncle, it extends through the jugular foramen, then passing into the carotid sheath between the internal carotid artery and the internal jugular vein down below the head, to the neck, chest and abdomen, where it contributes to the innervation of the viscera. Besides output to the various organs in the body, the vagus nerve conveys sensory information about the state of the body's organs to the central nervous system. 80-90% of the nerve fibers in the vagus nerve are afferent (sensory) nerves communicating the state of the viscera to the brain. The medieval Latin word vagus means literally "wandering" (the words vagrant, vagabond, and vague come from the same root). Sometimes the branches are spoken of in the plural and are thus called vagi (/ˈveɪdʒaɪ/, US dict: vā′·jī). The vagus is also called the pneumogastric nerve since it innervates both the lungs and the stomach. The motor division of the vagus nerve is derived from the basal plate of the
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    190
    Hepatic portal vein

    Hepatic portal vein

    The hepatic portal vein is a blood vessel that conducts blood from the gastrointestinal tract and spleen to the liver. This blood is rich in nutrients that were extracted from food, and the liver processes these nutrients; it also filters toxins that may have been ingested with the food. The liver receives about 75% of its blood through the hepatic portal vein, with the remainder coming from the hepatic artery proper. The blood leaves the liver to the heart in the hepatic veins. The hepatic portal vein is not a true vein, because it conducts blood to capillary beds in the liver and not directly to the heart. It is a major component of the hepatic portal system, one of only two portal venous systems in the body. The other is the hypophyseal portal system. The hepatic portal vein is usually formed by the confluence of the superior mesenteric and splenic veins and also receives blood from the inferior mesenteric, gastric, and cystic veins. Conditions involving the hepatic portal vein cause considerable illness and death. An important example of such a condition is elevated blood pressure in the hepatic portal vein. This condition, called portal hypertension, is a major complication of
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    191
    Atlas

    Atlas

    In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine. It is named for the Atlas of Greek mythology, because it supports the globe of the head. The atlas is the topmost vertebra, and – along with the Axis – forms the joint connecting the skull and spine. The atlas and axis are specialized to allow a greater range of motion than normal vertebrae. They are responsible for the nodding and rotation movements of the head. The atlanto-occipital joint allows the head to nod up and down on the vertebral column. The dens acts as a pivot that allows the atlas and attached head to rotate on the axis, side to side. The Atlas' chief peculiarity is that it has no body, it is ring-like, and consists of an anterior and a posterior arch and two lateral masses. The Atlas and Axis are important neurologically because the brain stem extends down to the Axis. The anterior arch forms about one-fifth of the ring: its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles and the anterior longitudinal ligament; posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for
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    192
    Bartholin's gland

    Bartholin's gland

    The Bartholin's glands (also called Bartholin glands or greater vestibular glands) are two glands located slightly posterior and to the left and right of the opening of the vagina. They secrete mucus to lubricate the vagina and are homologous to bulbourethral glands in males. However, while Bartholin's glands are located in the superficial perineal pouch in females, bulbourethral glands are located in the deep perineal pouch in males. They secrete mucus to provide vaginal lubrication. Bartholin's glands secrete relatively minute amounts (one or two drops) of fluid when a woman is sexually aroused. The minute droplets of fluid were once believed to be important for lubricating the vagina, but research from Masters and Johnson demonstrated that vaginal lubrication comes from deeper within the vagina. The fluid may slightly moisten the labial opening of the vagina, serving to make contact with this sensitive area more comfortable for the woman. Although unusual, it is possible for the Bartholin's glands to become irritated or infected, resulting in pain. If the duct becomes obstructed, a Bartholin's cyst can develop, and a Bartholin's cyst in turn can become infected and form an
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    193
    Mandibular nerve

    Mandibular nerve

    The mandibular nerve (V3) is the largest of the three branches of the trigeminal nerve. It is made up of two roots: The two roots (sensory and motor) exit the middle cranial fossa through the foramen ovale. The two roots then combine. Immediately in the infratemporal fossa beneath the base of the skull, the nerve gives off two branches from its medial side: a recurrent branch (nervus spinosus) and the nerve to the medial pterygoid muscle. The mandibular nerve then divides into two trunks, an anterior and a posterior. The mandibular nerve gives off the following branches: The mandibular nerve also gives off branches to the otic ganglion The mandibular nerve innervates:
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    194
    Medulla oblongata

    Medulla oblongata

    The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and deals with autonomic, involuntary functions, such as breathing, heart rate and blood pressure. The medulla is often thought of as being in two parts: The region between the anterior median sulcus and the anterolateral sulcus is occupied by an elevation on either side known as the pyramid of medulla oblongata. This elevation is caused by the corticospinal tract. In the lower part of the medulla some of these fibers cross each other thus obliterating the anterior median fissure. This is known as the decussation of the pyramids. Some other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as the external arcuate fibers. The region between the anterolateral and posterolateral sulcus in the upper part of the medulla is marked by a swelling known as the Olivary body. It is caused by a large mass of gray matter known as the
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    195
    Putamen

    Putamen

    The putamen is a round structure located at the base of the forebrain (telencephalon). The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus. The main function of the putamen is to regulate movements and influence various types of learning. It employs dopamine to perform its functions. The putamen also plays a role in degenerative neurological disorders, such as Parkinson's disease. The word "putamen" is from Latin, referring to that which "falls off in pruning", from "puto", meaning "to prune". It is pronounced pyu-ta'men. Until recently, very few studies were conducted that were focused specifically on the putamen. However, many studies have been done on the basal ganglia and the interactions among the brain structures it comprises. In the 1970s, the first single unit recordings were done with monkeys monitoring pallidal neuron activity related to movement. The putamen is a structure in the forebrain. Along with the caudate nucleus it forms the dorsal striatum. The caudate and putamen contain the same types
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    196
    Retroperitoneum

    Retroperitoneum

    The retroperitoneal space (retroperitoneum) is the anatomical space in the abdominal cavity behind (retro) the peritoneum. It has no specific delineating anatomical structures. Organs are retroperitoneal if they have peritoneum on their anterior side only. Structures that are not suspended by mesentery in the abdominal cavity and that lie between the parietal peritoneum and abdominal wall are classified as retroperitoneal. The retroperitoneum can be further subdivided into the following: Structures that lie behind the peritoneum are termed "retroperitoneal". Organs that were once suspended within the abdominal cavity by mesentery but migrated posterior to the peritoneum during the course of embryogenesis to become retroperitoneal are considered to be secondarily retroperitoneal organs. A useful mnemonic to aid recollection of the abdominal retroperitoneal viscera is SAD PUCKER, or DUKE CRAPS: Another mnemonic going along with SAD PUCKER is 112 212111, this correlating to which ones are Primarily (1) or Secondarily (2) Retroperitoneal. Bounded by the anterior and posterior leafs of the renal fascia. It contains the following structures: Bounded by the posterior layer of peritoneum
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    197
    Substantia nigra

    Substantia nigra

    The substantia nigra is a brain structure located in the mesencephalon (midbrain) that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", reflecting the fact that parts of the substantia nigra appear darker than neighboring areas. This is due to high levels of melanin in dopaminergic neurons. Parkinson's disease is characterized by the death of dopaminergic neurons in the substantia nigra pars compacta. Although the substantia nigra appears as a continuous band in brain sections, anatomical studies have found that it actually consists of two parts with very different connections and functions, the pars compacta and pars reticulata. The pars compacta serves mainly as an input to the basal ganglia circuit, supplying the striatum with dopamine. The pars reticulata, on the other hand, serves mainly as an output, conveying signals from the basal ganglia to numerous other brain structures. The substantia nigra, along with four other nuclei, is part of the basal ganglia. The substantia nigra lies in the midbrain, dorsal to the cerebral peduncles. Humans have two substantiae nigrae, one on each side of the midline. The substantia
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    198
    Vas deferens

    Vas deferens

    The vas deferens (plural: vasa deferentia), also called ductus deferens (Latin: "carrying-away vessel"; plural: ductus deferentes), is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation. There are two ducts, connecting the left and right epididymis to the ejaculatory ducts in order to move sperm. Each tube is about 30 centimeters long (in humans) and is muscular (surrounded by smooth muscle). Its epithelium is lined by stereocilia. They are part of the spermatic cords. During ejaculation the smooth muscle in the walls of the vas deferens contracts reflexively, thus propelling the sperm forward. This is also known as peristalsis. The sperm is transferred from the vas deferens into the urethra, collecting secretions from the male accessory sex glands such as the seminal vesicles, prostate gland and the bulbourethral glands, which form the bulk of semen. The procedure of deferentectomy, also known as a vasectomy, is a method of contraception in which the vasa deferentia are permanently cut, though in some cases it can be reversed. A modern variation, which is also known as a vasectomy even though it does not include
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    199
    Acetabulum

    Acetabulum

    The acetabulum ( /æsɨˈtæbjʊləm/) is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. There are three bones of the os coxae (hip bone) that come together to form the acetabulum. Contributing a little more than two-fifths of the structure is the ischium, which provides lower and side boundaries to the acetabulum. The ilium forms the upper boundary, providing a little less than two-fifths of the structure of the acetabulum. The rest is formed by the pubis, near the midline. It is bounded by a prominent uneven rim, which is thick and strong above, and serves for the attachment of the acetabular labrum, which reduces its opening, and deepens the surface for formation of the hip joint. At the lower part of the acetabulum is the acetabular notch, which is continuous with a circular depression, the acetabular fossa, at the bottom of the cavity of the acetabulum. The rest of the acetabulum is formed by a curved, crescent-moon shaped surface, the lunate surface, where the joint is made with the head of the femur. Its counterpart in the pectoral girdle is the glenoid fossa. In reptiles and in birds, the acetabula are deep
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    Cardiac muscle

    Cardiac muscle

    Cardiac muscle (heart muscle) is a type of involuntary striated muscle found in the walls and histological foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle. The cells that comprise cardiac muscle, called cardiomyocytes or myocardiocyteal muscle cells,can contain one, two, or very rarely three or four cell nuclei. Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems. This complex of actions makes up the systole of the heart. Cardiac muscle cells, like all tissues in the body, rely on an ample blood supply to deliver oxygen and nutrients and to remove waste products such as carbon dioxide. The coronary arteries fulfill this function. Cardiac muscle is adapted to be highly resistant to fatigue: it has a large number of mitochondria, enabling continuous aerobic respiration via oxidative phosphorylation, numerous myoglobins (oxygen-storing pigment) and a good blood supply, which provides nutrients and oxygen. The heart is so tuned to aerobic
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    Cingulate sulcus

    Cingulate sulcus

    The cingulate sulcus is a sulcus (brain fold) on the medial wall of the cerebral cortex. The frontal and parietal lobes are separated by the cingulate sulcus from the cingulate gyrus.
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    Mammary gland

    Mammary gland

    A mammary gland is an organ in female mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In humans, the mammary glands are situated on the breasts. In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders. The mammary glands of other mammals that have more than two breasts, such as dogs and cats, are sometimes called dugs. A mammary gland is a specific type of apocrine gland specialized for manufacture of colostrum when giving birth. Mammary glands can be identified as apocrine because they exhibit striking "decapitation" secretion. Many sources assert that mammary glands are modified sweat glands. Some authors dispute that and argue instead that they are sebaceous glands. The basic components of a mature mammary gland are the alveoli (hollow cavities, a few millimetres large) lined with milk-secreting cuboidal cells and surrounded by myoepithelial cells. These alveoli join up to form groups known as lobules, and each lobule has a lactiferous duct that drains into openings in the nipple. The myoepithelial cells can contract under the stimulation of oxytocin thereby excreting milk secreted from
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    Vagina

    Vagina

    The vagina (from Latin vāgīna, literally "sheath" or "scabbard") is a fibromuscular tubular tract which is a sex organ and has two main functions; sexual intercourse and childbirth. In humans, this passage leads from the opening of the vulva to the uterus (womb), but the vaginal tract ends at the cervix. Unlike men, who have only one genital orifice, women have two, the urethra and the vagina. The vaginal opening is much larger than the urethral opening, and both openings are protected by the labia. The inner mould of the vagina has a foldy texture which can create friction for the penis during intercourse. During arousal, the vagina gets moist to facilitate the entrance of the penis. The Latinate plural "vaginae" is rarely used in English. In casual conversation, the word vagina is often used to refer to the vulva or to the female genitals in general. The traditional dictionary definition refers exclusively to the specific internal structure. The human vagina is an elastic muscular canal that extends from the cervix to the vulva. The internal lining of the vagina consists of stratified squamous epithelium. Beneath this lining is a layer of smooth muscle, which may contract during
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    Cerebral peduncle

    Cerebral peduncle

    Mainly, the three common areas that give rise to the cerebral peduncles are the cortex, the spinal cord and the cerebellum. The cerebral peduncle, by most classifications, is everything in the mesencephalon except the tectum. The region includes the midbrain tegmentum, crus cerebri and pretectum. By this definition, the cerebral peduncles are also known as the basis pedunculi, while the large ventral bundle of efferent fibers is referred to as the crus cerebri or the pes pedunculi. There are numerous nerve tracts located within this section of the brainstem. Of note, in the cerebral peduncular loop fibers from motor areas of the brain project to the cerebral peduncle and then project to various thalamic nuclei. Important fibers running through the cerebral peduncles include the corticospinal tract and the corticobulbar tract, among others. This area contains many nerve tracts conveying motor information to and from the brain to the rest of the body.
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    Lesser occipital nerve

    Lesser occipital nerve

    The lesser occipital nerve or small occipital nerve is a cutaneous spinal nerve arising between the second and third cervical vertebrae, along with the greater occipital nerve. It innervates the scalp in the lateral area of the head posterior to the ear. It arises from the lateral branch of the ventral ramus of the second cervical nerve, sometimes also from the third; it curves around and ascends along the posterior border of the Sternocleidomastoideus. Near the cranium it perforates the deep fascia, and is continued upward along the side of the head behind the auricula, supplying the skin and communicating with the greater occipital, the great auricular, and the posterior auricular branch of the facial. The smaller occipital varies in size, and is sometimes duplicated. It gives off an auricular branch, which supplies the skin of the upper and back part of the auricula, communicating with the mastoid branch of the great auricular. This branch is occasionally derived from the greater occipital nerve. Disorder in this nerve causes occipital neuralgia. This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information
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    Taste bud

    Taste bud

    Taste buds contain the receptors for taste. They are located around the small structures on the upper surface of the tongue, soft palate, upper esophagus and epiglottis, which are called papillae. These structures are involved in detecting the five (known) elements of taste perception: salty, sour, bitter, sweet, and umami. Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves. On average, the human tongue has 2,000–8,000 taste buds. The majority of taste buds on the tongue sit on raised protrusions of the tongue surface called papillae. There are four types of papillae present in the human tongue: Salts, sweet, sour and umami tastes causes depolarization of the taste cells, although different mechanisms are applied. Bitter causes an internal release of Ca2+, no external Ca2+ is required. The bud is formed by two kinds of cells:
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    Anterior cruciate ligament

    Anterior cruciate ligament

    The anterior cruciate ligament (ACL) is a cruciate ligament which is one of the four major ligaments of the human knee. In the quadruped stifle (analogous to the knee), based on its anatomical position, it is also referred to as the cranial cruciate ligament. The ACL originates from deep within the notch of the distal femur. Its proximal fibers fan out along the medial wall of the lateral femoral condyle. There are two bundles of the ACL—the anteromedial and the posterolateral, named according to where the bundles insert into the tibial plateau. The ACL attaches in front of the intercondyloid eminence of the tibia, being blended with the anterior horn of the medial meniscus. These attachments allow it to resist anterior translation and medial rotation of the tibia, in relation to the femur. The ACL is quite commonly injured in athletes of varying sports. These situations are often remedied by surgery followed by several months of physical therapy. A 2010 Los Angeles Times review of two seemingly conflicting medical studies discussed whether ACL reconstruction was advisable. One study found that children under 14 who had ACL reconstruction fared better after early surgery than those
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    Brachial artery

    Brachial artery

    The brachial artery is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries which run down the forearm. In some individuals, the bifurcation occurs much earlier and the ulnar and radial arteries extend through the upper arm. The pulse of the brachial artery is palpable on the anterior aspect of the elbow, medial to the tendon of the biceps, and, with the use of a stethoscope and sphygmomanometer (blood pressure cuff) often used to measure the blood pressure. The brachial artery is closely related to the median nerve; in proximal regions, the median nerve is immediately lateral to the brachial artery. Distally, the median nerve crosses the medial side of the brachial artery and lies anterior to the elbow joint. as well as important anastomotic networks of the elbow and (as the axillary artery) the shoulder. The biceps head is lateral to the brachial artery. The median nerve is medial to the brachial artery for most of its course.
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    Colon

    Colon

    The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided (largely bacterial) fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a major role in absorption of foods and nutrients. However, the colon does absorb water, sodium and some fat soluble vitamins. In mammals, the colon consists of four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon (the proximal colon usually refers to the ascending colon and transverse colon). The cecum, colon, rectum and anal canal make up the large intestine. The location of the parts of the colon is either in the abdominal cavity (intraperitoneal) or behind it in the retroperitoneum. Retroperitoneal organs in general do not have a complete covering of peritoneum, so they are fixed in location. Intraperitoneal organs are completely surrounded by peritoneum and are therefore mobile. Of the colon, the ascending colon, descending colon and rectum are retroperitoneal, while the caecum, appendix, transverse colon and sigmoid
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    Ethmoid bone

    Ethmoid bone

    The ethmoid bone (/ˈɛθmɔɪd/; from Greek ethmos, "sieve") is a bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits. The cubical bone is lightweight due to a spongy construction. The ethmoid bone is one of the bones that makes up the orbit of the eye. The ethmoid has three parts: the cribriform plate, the ethmoidal labyrinth, and the perpendicular plate. The ethmoid articulates with fifteen bones: Fracture of the lamina papyracea, the lateral plate of the ethmoid labyrinth bone, permits communication between the nasal cavity and the ipsilateral orbit through the inferomedial orbital wall, resulting in orbital emphysema. Increased pressure within the nasal cavity, as seen during sneezing, for example, leads to temporary exophthalmos. The porous, fragile nature of the ethmoid bone makes it particularly susceptible to fractures. The ethmoid is usually fractured from an upward force to the nose. This could occur by hitting the dashboard in a car crash or landing on the ground after a fall. The ethmoid fracture can produce bone fragments that penetrate the cribriform plate. This trauma can lead to a leak of
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    Extensor carpi ulnaris muscle

    Extensor carpi ulnaris muscle

    In human anatomy, the extensor carpi ulnaris is a skeletal muscle located on the ulnar side of the forearm. It acts to extend and adduct at the carpus/wrist. Being an extensor muscle, extensor carpi ulnaris is on the posterior side of the forearm. It originates from the lateral epicondyle of the humerus and the posterior border of the ulna, and crosses the forearm to the ulnar (medial) side to insert at the base of the 5th metacarpal. The extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint. The muscle is a minor extensor of the carpus in carnivores, but has become a flexor in ungulates. In this case it is described as ulnaris lateralis. Despite its name, the extensor carpi ulnaris is innervated by the deep branch of the radial nerve . It would therefore be paralyzed in an injury to the posterior cord of the brachial plexus.
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    Long thoracic nerve

    Long thoracic nerve

    The long thoracic nerve (external respiratory nerve of Bell; posterior thoracic nerve) supplies the Serratus anterior. This nerve characteristically arises by three roots from the fifth, sixth, and seventh cervical nerves (C5-C7) but the root from C7 may be absent. The roots from C5 and C6 pierce the Scalenus medius, while the C7 root passes in front of the muscle. The nerve descends behind the brachial plexus and the axillary vessels, resting on the outer surface of the Serratus anterior. It extends along the side of the thorax to the lower border of that muscle, supplying filaments to each of its digitations (finger-like projections). Due to its long, relatively superficial course, it is susceptible to injury either through direct trauma or stretch. Injury has been reported in almost all sports, typically occurring from a blow to the ribs underneath an outstretched arm. The long thoracic nerve can also be damaged during surgery for breast cancer, specifically radical mastectomies that involve removal of axillary lymph nodes. Injuries to the nerve can result from carrying heavy bags over the shoulder for a prolonged time. There are also reports of isolated damage to this nerve as
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    Papillary muscle

    Papillary muscle

    In anatomy, the papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves (a.k.a. the mitral and tricuspid valves) via the chordae tendinae and contract to prevent inversion or prolapse of these valves. There are five total papillary muscles in the heart, three in the right ventricle and two in the left. The anterior, posterior, and septal papillary muscles of the right ventricle each attach via chordae tendineae to the tricuspid valve. The anterior and posterior papillary muscles of the left ventricle attach via chordae tendineae to the mitral valve. The papillary muscles of both the right and the left ventricles begin to contract shortly before ventricular systole and maintain tension throughout. This prevents regurgitation--backward flow of ventricular blood into the atrial cavities--by bracing the atrioventricular valves against prolapse--being forced back into the atria by the high pressure in the ventricles. Papillary muscle rupture, as can be caused by a heart infarct, and dysfunction, as can be caused by ischemia, can both lead to the complication of mitral valve prolapse.
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    Temporomandibular joint

    Temporomandibular joint

    The temporomandibular joint is the joint of the jaw and is frequently referred to as TMJ. There are two TMJs, one on each side, working in unison. The name is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium (skull), and the lower jaw bone called the mandible. The unique feature of the TMJs is the articular disc. The disc is composed of fibrocartilagenous tissue (like the firm and flexible elastic cartilage of the ear) which is positioned between the two bones that form the joint. The TMJs are one of the few synovial joints in the human body with an articular disc, another being the sternoclavicular joint. The disc divides each joint into two. The lower joint compartment formed by the mandible and the articular disc is involved in rotational movement—this is the initial movement of the jaw when the mouth opens. The upper joint compartment formed by the articular disk and the temporal bone is involved in translational movement—this is the secondary gliding motion of the jaw as it is opened widely. The part of the mandible which mates to the under-surface of the disc is the condyle and the part of the temporal bone which mates to
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    Ulnar nerve

    Ulnar nerve

    In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body (meaning unprotected by muscle or bone), so injury is common. This nerve is directly connected to the little finger, and the adjacent half of the ring finger, supplying the palmar side of these fingers, including both front and back of the tips, perhaps as far back as the fingernail beds. One method of injuring the nerve is to strike the medial epicondyle of the humerus from posteriorly, or inferiorly with the elbow flexed. The ulnar nerve is trapped between the bone and the overlying skin at this point. This is commonly referred to as bumping one's "funny bone". This name is thought to be a pun, based on the sound resemblance between the name of the bone of the upper arm, the "humerus" and the word "humorous". Alternatively, according to the Oxford English Dictionary it may refer to "the peculiar sensation experienced when it is struck". The ulnar nerve originates from the C8-T1 nerve roots which form part of the medial cord of the brachial plexus, and descends on
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    Ventricular system

    Ventricular system

    The ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord. The system comprises four ventricles: There are several small holes or foramina that connect these ventricles, though only the first two of the list below are generally considered part of the ventricular system: The ventricles are filled with cerebrospinal fluid (CSF) which bathes and cushions the brain and spinal cord within their bony confines. Cerebrospinal fluid is produced by modified ependymal cells of the choroid plexus found in all components of the ventricular system except for the cerebral aqueduct and the posterior and anterior horns of the lateral ventricles. CSF flows from the lateral ventricles via the foramina of Monro into the third ventricle, and then the fourth ventricle via the cerebral aqueduct in the brainstem. From there it can pass into the central canal of the spinal cord or into the cisterns of the subarachnoid space via three small foramina: the central foramen of Magendie and the two lateral foramina of Luschka. The fluid then flows around the superior sagittal sinus to be reabsorbed via the arachnoid villi
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    Flexor carpi radialis muscle

    Flexor carpi radialis muscle

    In anatomy, flexor carpi radialis is a muscle of the human forearm that acts to flex and (radial) abduct the hand. This muscle originates on the medial epicondyle of the humerus. It runs just laterally of flexor digitorum superficialis and inserts on the anterior aspect of the base of the second metacarpal, and has small slips to both the third metacarpal and trapezial tuberosity. On the anterior aspect of a person's forearm, proximal to the wrist, flexor carpi radialis is the most lateral (closest to the thumb) tendon visible when the wrist is brought into flexion. As are most of the flexors of the hand, FCR is innervated by the median nerve. It gets its blood from the ulnar artery. The muscle, like all flexors of the forearm, can be strengthened by exercises that resist its flexion. A wrist roller can be used and wrist curls with dumbbells can also be performed.
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    Greater auricular nerve

    Greater auricular nerve

    The great auricular nerve originates from the cervical plexus, composed of branches of spinal nerves C2 and C3. It provides sensory innervation for the skin over parotid gland and mastoid process, and both surfaces of the outer ear. Although this nerve is frequently referred to as the "greater" auricular nerve, this is not the proper nomenclature since there is no "lesser" auricular nerve. Great refers to the distinction between it and the Auriculotemporal nerve, which is the less influential of the two. It is the largest of the ascending branches. It arises from the second and third cervical nerves, winds around the posterior border of the Sternocleidomastoideus, and, after perforating the deep fascia, ascends upon that muscle beneath the Platysma to the parotid gland, where it divides into an anterior and a posterior branch. This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    Stapes

    Stapes

    The stapes is the stirrup-shaped small bone or ossicle in the middle ear which is attached through the incudostapedial joint to the incus laterally and to the fenestra ovalis, the "oval window", medially. Stapes means stirrup in Latin. The oval window is adjacent to the vestibule of the inner ear. The stapes is the smallest and lightest bone in the human body. It was described by the professor Giovanni Filippo Ingrassia in 1546 at the University of Naples. The stapes transmits the sound vibrations from the incus to the membrane of the inner ear inside the fenestra ovalis. The stapes is also stabilized by the stapedius muscle, which is innervated by the facial nerve. In non-mammalian tetrapods, the bone homologous to the stapes is usually called the columella; however, in reptiles, either term may be used. In fish, the homologous bone is called the hyomandibular, and is part of the gill arch supporting either the spiracle or the jaw, depending on species. As the stapes first develops embryologically from the 6th to 8th week of life, it surrounds the stapedial artery, which supplies the majority of the vasculature of the embryonic head. After that period, the external carotid artery
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    Brachiocephalic vein

    Brachiocephalic vein

    The left and right brachiocephalic veins (or innominate veins) in the upper chest are formed by the union of each corresponding internal jugular vein and subclavian vein. This is at the level of the sternoclavicular joint. These great vessels merge to form the superior vena cava. The brachiocephalic veins are the major veins returning blood to the superior vena cava.
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    Distal convoluted tubule

    Distal convoluted tubule

    The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting duct system. It is partly responsible for the regulation of potassium, sodium, calcium, and pH. It is the primary site for the kidneys' hormone based regulation of calcium (Ca). On its apical surface (lumen side), cells of the DCT have a thiazide-sensitive Na-Cl cotransporter and are permeable to Ca, via TRPV5 channel. On the basolateral surface (blood) there is an ATP dependent Na/K antiport pump, a secondary active Na/Ca transporter-- antiport, and an ATP dependent Ca transporter. The basolateral ATP dependent Na/K pump produces the gradient for Na to be absorbed from the apical surface via the Na/Cl synport and for Ca to be reclaimed into the blood by the Na/Ca basolateral antiport. Thiazide diuretics inhibit Na/Cl reabsorption from the DCT by blocking the thiazide-sensitive Na-Cl cotransporter. By inhibiting the cotransporter, thiazide diuretics increase the gradient potential for Na. This increases the activity of the basolateral Na/Ca antiport and causes the increase in calcium reclamation associated with thiazide diuretics. The DCT is lined with simple cuboidal
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    Fibularis longus

    Fibularis longus

    In human anatomy, the peroneus longus (also known as fibularis longus) is a superficial muscle in the lateral compartment of the leg, and acts to evert and plantar flex the ankle. The muscle, the longest and most superficial of the three peroneus muscles, is attached proximally to the head of the fibula and its 'belly' runs down most of this bone. It becomes a tendon that goes posteriorly around the lateral malleolus of the ankle, then continues under the foot to attach to the medial cuneiform and first metatarsal. The terms Peroneus (i.e., Longus and Brevis) and Peroneal (i.e., Artery, Retinaculum) are derived from the Greek word Perone (pronounced Pair-uh-knee) meaning pin of a brooch or a buckle. In medical terminology, both terms refer to being of or relating to the fibula or to the outer portion of the leg. It arises from the head and upper two-thirds of the lateral surface of the body of the fibula, from the deep surface of the fascia, and from the intermuscular septa between it and the muscles on the front and back of the leg; occasionally also by a few fibers from the lateral condyle of the tibia. Between its attachments to the head and to the body of the fibula there is a
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    Levator ani

    Levator ani

    The levator ani is a broad, thin muscle, situated on the side of the pelvis. It is attached to the inner surface of the side of the lesser pelvis, and unites with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity. It supports the viscera in pelvic cavity, and surrounds the various structures which pass through it. In combination with the coccygeus muscle, it forms the pelvic diaphragm. The levator ani is divided into three parts: The levator ani arises, in front, from the posterior surface of the superior ramus of the pubis lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia. Posteriorly, this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a varying distance above the arch, in some cases reaching nearly as high as the canal for the obturator vessels and nerve. The fibers pass downward and backward to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the coccyx; those placed more
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    Raphe nuclei

    Raphe nuclei

    The raphe nuclei ("raffe", Greek: ραφή = seam) are a moderate-size cluster of nuclei found in the brain stem. Their main function is to release serotonin to the rest of the brain. Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act in these nuclei, as well as at their targets. The raphe nuclei are traditionally considered to be the medial portion of the reticular formation, and they appear as a ridge of cells in the center and most medial portion of the brain stem. In order from caudal to rostral, the raphe nuclei are known as the nucleus raphe obscurus, the raphe magnus, the raphe pontis, the raphe pallidus, the nucleus centralis superior, nucleus raphe dorsalis, nuclei linearis intermedius and linearis rostralis. Some scientists chose to group the linearis nuclei into one nucleus, shrinking the number of raphe to seven, e.g., NeuroNames makes the following ordering: These nuclei interact with almost every pertinent portion of the brain, but only a few of them have specifically independent interaction. These select nuclei are discussed as follows. Overall, the caudal raphe nuclei, including the raphe magnus, pallidus and raphe obscurus, all project
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    Saccule

    Saccule

    The saccule is a bed of sensory cells situated in the inner ear. The saccule translates head movements into neural impulses which the brain can interpret. The saccule is sensitive to linear translations of the head, specifically movements up and down (for example, moving on an elevator). When the head moves vertically, the sensory cells of the saccule are disturbed and the neurons connected to them begin transmitting impulses to the brain. These impulses travel along the vestibular portion of the eighth cranial nerve to the vestibular nuclei in the brainstem. The vestibular system is important in maintaining balance, or equilibrium. The vestibular system includes the saccule, utricle, and the three semicircular canals. The vestibule is the name of the fluid-filled, membranous duct than contains these organs of balance. The vestibule is encased in the temporal bone of the skull. The saccule, or sacculus, is the smaller of the two vestibular sacs. It is globular in form and lies in the recessus sphæricus near the opening of the scala vestibuli of the cochlea. Its cavity does not directly communicate with that of the utricle. The anterior part of the saccule exhibits an oval
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    Scaphoid bone

    Scaphoid bone

    The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb-side of the wrist (also called the lateral or radial side). It forms the radial border of the carpal tunnel. The scaphoid bone is the largest bone of the proximal row of wrist bones, its long axis being from above downward, lateralward, and forward. It is approximately the size and shape of a medium sized cashew. The etymology of the scaphoid bone (Greek: σφηνῳδής) is derived from the Greek skaphos which means "a boat," and the Greek eidos which means "kind". This refers to the shape of the bone, supposedly reminiscent of a boat, and in older literature on human anatomy the scaphoid is referred to as the navicular bone of the hand, since there is also a bone in a similar position in the foot, called the navicular. In reptiles, birds, and amphibians, this bone is instead commonly referred to as the radiale, because of its articulation with the radius. The superior surface is convex, smooth, of triangular shape, and articulates with the lower end of the radius. The inferior surface, directed downward, backward and laterally is also smooth, convex, and triangular, and is
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    Soft palate

    Soft palate

    The soft palate (also known as velum or muscular palate) is the soft tissue constituting the back of the roof of the mouth. The soft palate is distinguished from the hard palate at the front of the mouth in that it does not contain bone. The soft palate is movable, consisting of muscle fibers sheathed in mucous membrane. It is responsible for closing off the nasal passages during the act of swallowing, and also for closing off the airway. During sneezing, it protects the nasal passage by diverting a portion of the excreted substance to the mouth. The uvula hangs from the end of the soft palate. Research shows that the uvula is not actually involved in snoring processes. This has been shown through inconsistent results from uvula removal surgery. Snoring is more closely associated with fat deposition in the pharynx, enlarged tonsils of Waldeyer's ring, or deviated septum problems. Touching the uvula or the end of the soft palate evokes a strong gag reflex in most people. A speech sound made with the middle part of the tongue (dorsum) touching the soft palate is known as a velar consonant. It is possible for the soft palate to retract and elevate during speech to separate the oral
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    Superior vena cava

    Superior vena cava

    The superior vena cava (also known as the cava or cva) is a large diameter, yet short, vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium. It is located in the anterior right superior mediastinum. It is formed by the left and right brachiocephalic veins (also referred to as the innominate veins), which also receive blood from the upper limbs, eyes and neck, behind the lower border of the first right costal cartilage. The azygos vein joins it just before it enters the right atrium, at the upper right front portion of the heart. It is also known as the cranial vena cava in animals. No valve divides the superior vena cava from the right atrium. As a result, the (right) atrial and (right) ventricular contractions are conducted up into the internal jugular vein and, through the sternocleidomastoid muscle, can be seen as the jugular venous pressure. In tricuspid valve regurgitation, these pulsations are very strong.
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    Utricle

    Utricle

    The utricle, or utriculus, along with the saccule is one of the two otolith organs located in the vertebrate inner ear. The utricle and the saccule are parts of the balancing apparatus (membraneous labyrinth) located within the vestibule of the bony labyrinth (small oval chamber). These use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle is larger than the saccule and is of an oblong form, compressed transversely, and occupies the upper and back part of the vestibule, lying in contact with the recessus ellipticus and the part below it. The utricle contains mechanoreceptors called hair cells that distinguish between degrees of tilting of the head, thanks to their apical stereocilia set-up. These are covered by otolith which, due to gravity, pull on the stereocilia and tilt them. Depending on whether the tilt is in the direction of the kinocilium or not, the resulting hair cell polarisation is excitatory (depolarising) or inhibitory (hyperpolarisation), respectively. Any orientation of the head causes a combination of stimulation to the utricles and saccules of the two ears. The brain interprets head orientation by comparing
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    Abdominal cavity

    Abdominal cavity

    The abdominal cavity is the body cavity of the human body (and animal bodies) that holds the bulk of the viscera. It is located below (or inferior to) the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm (a thin sheet of muscle under the lungs), and its oblique floor is the pelvic inlet (the superior opening of the pelvis). It is a part of the abdominopelvic cavity. It is well connected with the pleural (thoracic) cavity. Organs of the abdominal cavity include the stomach, liver, gallbladder, spleen, pancreas, small intestine, kidneys, and large intestine. The abdominal cavity is lined with a protective membrane termed the peritoneum. The kidneys are located in the abdominal cavity behind the peritoneum, in the retroperitoneum. The viscera are also covered, in the front, with a layer of peritoneum called the greater omentum (or omental apron).
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    Arachnoid granulation

    Arachnoid granulation

    Arachnoid granulations (or arachnoid villi) are small protrusions of the arachnoid (the thin second layer covering the brain) through the dura mater (the thick outer layer). They protrude into the venous sinuses of the brain, and allow cerebrospinal fluid (CSF) to exit the sub-arachnoid space and enter the blood stream. Largest granulations lie along the superior sagittal sinus, a large venous space running from front to back along the centre of the head (on the inside of the skull). They are, however, present along other dural sinuses as well. Smaller granulations are called villi, large calcified ones are referred to as pacchionian bodies. The arachnoid granulations act as one-way valves. Normally the pressure of the CSF is higher than that of the venous system, so CSF flows through the villi and granulations into the blood. If the pressure is reversed for some reason, fluid will not pass back into the subarachnoid space (of the brain). The reason for this is not known. It has been suggested that the endothelial cells of the venous sinus create vacuoles of CSF, which move through the cell and out into the blood. The importance of arachnoid granulations for the drainage of CSF is
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    Capitate bone

    Capitate bone

    In the human hand, the capitate bone is the largest of the carpal bones, and occupies the center of the wrist. It presents, above, a rounded portion or head, which is received into the concavity formed by the scaphoid and lunate bones; a constricted portion or neck; and below this, the body. The bone is also found in many other mammals, and is homologous with the "third distal carpal" of reptiles and amphibians. The etymology derives from the Latin capitātus, "having a head," from capit-, meaning "head." The superior surface is round, smooth, and articulates with the lunate bone. The inferior surface is divided by two ridges into three facets, for articulation with the second, third, and fourth metacarpal bones, that for the third being the largest. The dorsal surface is broad and rough. The volar surface is narrow, rounded, and rough, for the attachment of ligaments and a part of the Adductor pollicis muscle. The lateral surface articulates with the lesser multangular by a small facet at its anterior inferior angle, behind which is a rough depression for the attachment of an interosseous ligament. Above this is a deep, rough groove, forming part of the neck, and serving for the
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    Cranial nerves

    Cranial nerves

    Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum; the remaining ten pairs emerge from the brainstem. Human cranial nerves are nerves similar to those found in many other vertebrates. Cranial nerves XI and XII evolved in other species to amniotes (non-amphibian tetrapods), thus totaling twelve pairs. In some primitive cartilaginous fishes, such as the spiny dogfish or mud shark (Squalus acanthias), there is a terminal nerve numbered zero, since it exits the brain before the traditionally designated first cranial nerve. Because they exit from the brainstem as opposed to the spinal column, these are part of the central nervous system. As the list is important to keep in mind during the examination of the nervous system, there are many mnemonic devices in circulation to help remember the names and order of the cranial nerves. Because the mind recalls rhymes well, the best mnemonics often use rhyming schemes. An example mnemonic sentence for the initial letters
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    Deltoid muscle

    Deltoid muscle

    In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central nervous system. It was previously called the Deltoideus and the name is still used by some anatomists. It is called so because it is in the shape of the Greek letter Delta (triangle). It is also known as the common shoulder muscle, particularly in lower animals (e.g., in domestic cats). Deltoid is also further shortened in slang as "delt". The plural forms of all three incarnations are deltoidei, deltoids and delts. A study of 30 shoulders revealed an average weight of 191.9 grams (6.77 oz) (range 84 grams (3.0 oz)–366 grams (12.9 oz)) in humans. The deltoid originates in three distinct sets of fibers, often referred to as "heads": Fick divided these three groups of fibers, often referred to as parts (Latin: pars) or bands, into seven functional components: the anterior part has two components (I and II); the lateral one (III); and the posterior four (IV, V, VI, and VII) components. In
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    Exocrine gland

    Exocrine gland

    In the animal kingdom, the general term gland falls into two major categories with further subtypes falling under each of these. An Exocrine gland is distinguished by the fact that it excretes its essential product by way of a duct to some environment external to itself, be it either inside the body or on a surface of the body. Examples of exocrine glands include the sweat glands, salivary glands, mammary glands, pancreas and liver. An Endocrine gland is its counterpart. It secretes its essential product without the use of a duct directly into the bloodstream or else by diffusion into its surrounding tissue (paracrine signaling) where it often affects only target cells near the release site. Examples of endocrine glands include the adrenal glands, located atop the kidneys and responsible for the secretion of certain hormones such as adrenaline, cortisol and others. The testes, sing: testicle, in males and ovaries in females are not only gonads, organs which generate male and female germ cells respectively, but are also endocrine glands in that they produce various androgens and estrogens together known as steroidal sex hormones. Exocrine glands contain a glandular portion and a
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    Foramen magnum

    Foramen magnum

    In anatomy, the foramen magnum (Latin: 'great hole') is a large opening in the occipital bone of the cranium. It is one of the several oval or circular apertures in the base of the skull (the foramina), through which the medulla oblongata (an extension of the spinal cord) enters and exits the skull vault. Apart from the transmission of the medulla oblongata and its membranes, the foramen magnum transmits the spinal accessory nerve, vertebral arteries, the anterior and posterior spinal arteries, the membrana tectoria and alar ligaments. In humans, the foramen magnum is farther underneath the head than in great apes. Thus, in humans, the neck muscles (including the occipitofrontalis muscle) do not need to be as robust in order to hold the head upright. Comparisons of the position of the foramen magnum in early hominid species are useful to determine how comfortable a particular species was when walking on two limbs (bipedalism) rather than four (quadrupedalism). This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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    Frontal lobe

    Frontal lobe

    The frontal lobe is an area in the brain of mammals, located at the front of each cerebral hemisphere and positioned anterior to (in front of) the parietal lobe and superior and anterior to the temporal lobes. It is separated from the parietal lobe by a space between tissues called the central sulcus, and from the temporal lobe by a deep fold called the lateral (Sylvian) sulcus. The precentral gyrus, forming the posterior border of the frontal lobe, contains the primary motor cortex, which controls voluntary movements of specific body parts. The frontal lobe contains most of the dopamine-sensitive neurons in the cerebral cortex. The dopamine system is associated with reward, attention, short-term memory tasks, planning, and motivation. Dopamine tends to limit and select sensory information arriving from the thalamus to the fore-brain. A report from the National Institute of Mental Health says a gene variant that reduces dopamine activity in the prefrontal cortex is related to poorer performance and inefficient functioning of that brain region during working memory tasks, and to slightly increased risk for schizophrenia. On the lateral surface of the human brain, the central sulcus
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    Greater occipital nerve

    Greater occipital nerve

    The greater occipital nerve is a spinal nerve, specifically the medial branch of the dorsal primary ramus of cervical spinal nerve 2. This nerve arises from between the first and second cervical vertebrae, along with the lesser occipital nerve. It ascends after emerging from the suboccipital triangle obliquely between the inferior oblique and semispinalis capitis muscle. It then passes through the trapezius muscle and ascends to innervate the skin along the posterior part of the scalp to the vertex. It innervates the scalp at the top of the head, over the ear and over the parotid glands. Disorder of this nerve is one of the causes of cervicogenic headaches, referred to as occipital neuralgias. A common site, and usually misdiagnosed area of entrapment for the greater occipital nerve is at the obliquus capitis inferior muscle.
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    Hypothalamus

    Hypothalamus

    The hypothalamus (from Greek ὑπό = under and θάλαμος = room, chamber) is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus is located below the thalamus, just above the brain stem. In the terminology of neuroanatomy, it forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is roughly the size of an almond. The hypothalamus is responsible for certain metabolic processes and other activities of the autonomic nervous system. It synthesizes and secretes certain neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger, thirst, fatigue, sleep, and circadian cycles. The hypothalamus is a brain structure composed of distinct nuclei and less anatomically distinct areas. It is found in all vertebrate nervous systems. In mammals, the axons of magnocellular neurosecretory cells of the paraventricular nucleus and
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    Inguinal canal

    Inguinal canal

    The inguinal canal is a passage in the anterior (toward the front of the body) abdominal wall which in men conveys the spermatic cord and in women the round ligament. The inguinal canal is larger and more prominent in men. Each person has two, on the left and right sides of the abdomen. The inguinal canal is situated just above the medial half of the inguinal ligament. In both sexes the canal transmits the ilioinguinal nerve. Approximately 3.75 to 4 cm . It is obliquely directed anteroinferiorly and medially. A first-order approximation is to visualize the canal as a cylinder, To help define the boundaries, the canal is often further approximated as a box with six sides. Not including the two rings, the remaining four sides are usually called the "anterior wall", "posterior wall", "roof", and "floor". These consist of the following: The classic description of the contents of spermatic cord in the male are: 3 arteries: artery to vas deferens (or ductus deferens), testicular artery, cremasteric artery; 3 fascial layers: external spermatic, cremasteric, and internal spermatic fascia; 3 other structures: pampiniform plexus, vas deferens (ductus deferens), testicular lymphatics; 3
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    Latissimus dorsi muscle

    Latissimus dorsi muscle

    The latissimus dorsi (plural: latissimi dorsi), meaning 'broadest [muscle] of the back' (Latin latus meaning 'broad', latissimus meaning 'broadest' and dorsum meaning the back), is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm, and partly covered by the trapezius on its median dorsal region. The latissimus dorsi is responsible for extension, adduction, transverse extension also known as horizontal abduction, flexion from an extended position, and (medial) internal rotation of the shoulder joint. It also has a synergistic role in extension and lateral flexion of the lumbar spine. Due to bypassing the scapulothoracic joint and attaching directly to the spine, the actions the lat has on moving the arm can also influence the movement of the scapula, such as their downward rotation during a pull up. The number of dorsal vertebra to which it is attached vary from four to eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of the ilium. A muscular slip, the axillary arch, varying from 7 to 10 cm in length, and from 5 to 15 mm in breadth, occasionally springs from the upper edge of the latissimus dorsi about the middle of
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    Mesencephalon

    Mesencephalon

    The midbrain or mesencephalon (from the Greek mesos - middle, and enkephalos - brain) is a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation. Anatomically, it comprises the tectum (or corpora quadrigemina), tegmentum, the ventricular mesocoelia (or "iter"), and the cerebral peduncles, as well as several nuclei and fasciculi. Caudally the mesencephalon adjoins the pons (metencephalon) and rostrally it adjoins the diencephalon (Thalamus, hypothalamus, etc.). The midbrain is located below the cerebral cortex, and above the hindbrain placing it near the center of the brain. During embryonic development, the midbrain arises from the second vesicle, also known as the mesencephalon, of the neural tube. Unlike the other two vesicles, the prosencephalon and rhombencephalon, the mesencephalon remains undivided for the remainder of neural development. It does not split into other brain areas. while the prosencephalon, for example, divides into the telencephalon and the diencephalon. Throughout embryonic development, the cells within the midbrain continually multiply and compress the still-forming
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    Organ of Corti

    Organ of Corti

    The organ of Corti (or spiral organ) is the organ in the inner ear found only in mammals that contains auditory sensory cells, or "hair cells." The organ was named after the Italian anatomist Marquis Alfonso Giacomo Gaspare Corti (1822–1876), who conducted microscopic research of the mammalian auditory system. The organ of Corti has highly specialized structures that respond to fluid-borne vibrations in the cochlea with a shearing vector in the hairs of some cochlear hair cells. It contains between 15,000-20,000 auditory nerve receptors. Each receptor has its own hair cell. The shear on the hairs opens non-selective transduction ion channels that are permeable to potassium and calcium, leading to hair cell plasma membrane depolarization, activation of voltage-dependent calcium channels at the synaptic basolateral pole of the cells which triggers vesicle exocytosis and liberation of glutamate neurotransmitter to the synaptic cleft and electrical signaling to the auditory cortex via spiral ganglion neurons. The pinna and middle ear act as mechanical transformers and amplifiers, so that by the time sound waves reach the organ of Corti, their pressure amplitude is 22 times that of the
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    Pleural cavity

    Pleural cavity

    In human anatomy, the pleural cavity is the potential space between the two pleura (visceral and parietal) of the lungs. The pleura is a serous membrane which folds back onto itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural cavity; it normally contains a small amount of pleural fluid. The outer pleura (parietal pleura) is attached to the chest wall. The inner pleura (visceral pleura) covers the lungs and adjoining structures, viz. blood vessels, bronchi and nerves. The parietal pleura is highly sensitive to pain, while the visceral pleura is not, due to its lack of sensory innervation. The pleural cavity, with its associated pleurae, aids optimal functioning of the lungs during respiration. The pleural cavity also contains pleural fluid, which allows the pleurae to slide effortlessly against each other during ventilation. Surface tension of the pleural fluid also leads to close apposition of the lung surfaces with the chest wall. This relationship allows for greater inflation of the alveoli during respiration. The pleural cavity transmits movements of the chest wall to the lungs, particularly during heavy
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    Pons

    Pons

    The pons (pronounced /ˈpɔnz/) is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio (pons Varolii). It is cranial to the medulla oblongata, caudal to the midbrain, and ventral to the cerebellum. In humans and other bipeds, this means it is above the medulla, below the midbrain, and anterior to the cerebellum. This white matter includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus. The pons in humans measures about 2.5 cm in length. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. They connect the cerebellum to the pons and midbrain. The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Within the pons is the pneumotaxic center, a nucleus in the pons that regulates the
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    Rectum

    Rectum

    The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others. The human rectum is about 12 centimetres (4.7 in) long, and begins at the rectosigmoid junction (the end of the sigmoid colon), at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used. In humans, the rectum is followed by the anal canal, before the gut terminates at the anal verge. The rectum intestinum acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed from the feces. If defecation is delayed
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    Spermatic cord

    Spermatic cord

    The spermatic cord is the name given to the cord-like structure in males formed by the vas deferens and surrounding tissue that run from the abdomen down to each testicle. The pampiniform plexus, testicular artery, artery of the ductus deferens, lymphatic vessels, testicular nerves, and ductus deferens all run deep to the internal spermatic fascia. The genital branch of the genitofemoral nerve, cremasteric artery, and ilioinguinal nerve all run on the superficial surface of the external spermatic fascia. The classic and memorable description of the contents of spermatic cord in the male are: The spermatic cord is ensheathed in three layers of tissue: The spermatic cord is sensitive to torsion, in which the testicle rotates within its sac and kinks off its own blood supply. Testicular torsion may result in irreversible damage to the testicle within hours. A collection of serous fluid in the spermatic cord is named 'funiculocele'. The contents of the abdominal cavity may protrude into the inguinal canal, producing an indirect inguinal hernia.
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    Temporal lobe

    Temporal lobe

    The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in auditory perception and is home to the primary auditory cortex. It is also important for the processing of semantics in both speech and vision. The temporal lobe contains the hippocampus and plays a key role in the formation of long-term memory. The superior temporal gyrus includes an area (within the Sylvian fissure) where auditory signals from the cochlea (relayed via several subcortical nuclei) first reach the cerebral cortex. This part of the cortex (primary auditory cortex) is involved in hearing. Adjacent areas in the superior, posterior and lateral parts of the temporal lobes are involved in high-level auditory processing. In humans this includes speech, for which the left temporal lobe in particular seems to be specialized. Wernicke's area, which spans the region between temporal and parietal lobes, plays a key role (in tandem with Broca's area, which is in the frontal lobe). The functions of the left temporal lobe are not limited to low-level perception but extend to comprehension, naming,
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    Temporalis muscle

    Temporalis muscle

    The temporal muscle, also known as the temporalis, is one of the muscles of mastication. It covers much of the temporal bone. It arises from the temporal fossa and the deep part of temporal fascia. It passes medial to the zygomatic arch and inserts onto the coronoid process of the mandible. The temporal muscle is covered by the temporal fascia, also known as the temporal aponeurosis. The muscle is accessible on the temples, and can be seen and felt contracting while the jaw is clenching and unclenching. As with the other muscles of mastication, control of the temporal muscle comes from the third (mandibular) branch of the trigeminal nerve. Specifically, the muscle is innervated by the deep temporal nerves. The muscle receives its blood supply from the deep temporal arteries which anastomose with the middle temporal artery. Contraction of the temporal muscle retrudes and elevates the mandible. The posterior horizontal fibers retract the mandible while the anterior vertical fibers elevate the mandible. The temporalis is derived from the first pharyngeal arch in development.
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    Thumb

    Thumb

    The thumb is the first digit of the hand. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outer-most digit. The Medical Latin English noun for thumb is pollex (compare hallux for big toe), and the corresponding adjective for thumb is pollical. The English word "finger" has two senses, even in the context of appendages of a single typical human hand: Linguistically, it appears that the original sense was the broader of these two: penkwe-ros (also rendered as penqrós) was, in the inferred Proto-Indo-European language, a suffixed form of penkwe (or penqe), which has given rise to many Indo-European-family words (tens of them defined in English dictionaries) that involve or flow from concepts of fiveness. The thumb shares the following with each of the other four fingers: The thumb contrasts with each of the other four by being the only digit that: and hence the etymology of the word: "tum" is Proto-Indo-European for " swelling " (cf "tumour" and "thigh") since the thumb is the stoutest of the digits. In humans, opposition and apposition are two movements unique to the thumb but these words are not
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