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59-437: The hypoglossal nerve , also known as the twelfth cranial nerve , cranial nerve XII , or simply CN XII , is a cranial nerve that innervates all the extrinsic and intrinsic muscles of the tongue except for the palatoglossus , which is innervated by the vagus nerve . CN XII is a nerve with a sole motor function . The nerve arises from the hypoglossal nucleus in the medulla as a number of small rootlets, pass through

118-487: A "bag of worms" ( fasciculations ) or wasting ( atrophy ). The nerve is then tested by sticking the tongue out. If there is damage to the nerve or its pathways, the tongue will usually but not always deviate to one side, due to the genioglossus muscle receiving nerve signals on one side but not the other. When the nerve is damaged, the tongue may feel "thick," "heavy," or "clumsy." Weakness of tongue muscles can result in slurred speech, affecting sounds particularly dependent on

177-411: A branch from the anterior ramus of C1 . It then travels close to the vagus nerve and spinal division of the accessory nerve , spirals downwards behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath . At a point at the level of the angle of the mandible , the hypoglossal nerve emerges from behind the posterior belly of

236-411: A lack of complete separation between segments. The outer cells undergo a mesenchymal–epithelial transition to form an epithelium around each somite. The inner cells remain as mesenchyme . The Notch system, as part of the clock and wavefront model, forms the boundaries of the somites. DLL1 and DLL3 are Notch ligands , mutations of which cause various defects. Notch regulates HES1 , which sets up

295-419: A separate nerve over the course of evolution. The size of the hypoglossal nerve, as measured by the size of the hypoglossal canal, has been hypothesised to be associated with the progress of evolution of primates , with reasoning that larger nerves would be associated with improvements in speech associated with evolutionary changes. This hypothesis has been refuted. Cranial nerve Cranial nerves are

354-403: A series of roots in the fourth week of development, which have formed a single nerve and link to the tongue by the fifth week. The hypoglossal nerve provides motor control of the extrinsic muscles of the tongue: genioglossus , hyoglossus , styloglossus , and the intrinsic muscles of the tongue . These represent all muscles of the tongue except the palatoglossus muscle , which is innervated by

413-400: Is rostral to caudal (nose to tail gradient). Somites form one after the other down the length of the embryo from the head to the tail, with each new somite forming on the caudal (tail) side of the previous one. The timing of the interval is not universal. Different species have different interval timing. In the chick embryo, somites are formed every 90 minutes. In the mouse the interval

472-432: Is 2 hours. For some species, the number of somites may be used to determine the stage of embryonic development more reliably than the number of hours post-fertilization because rate of development can be affected by temperature or other environmental factors. The somites appear on both sides of the neural tube simultaneously. Experimental manipulation of the developing somites will not alter the rostral/caudal orientation of

531-664: Is fired via the stimulator lead in the neck, stimulating the hypoglossal nerve, and causing the tongue to protrude, thereby alleviating obstruction. The first recorded description of the hypoglossal nerve was by Herophilos (335–280 BC), although it was not named at the time. The first use of the name hypoglossal in Latin as nervi hypoglossi externa was used by Winslow in 1733. This was followed though by several different namings including nervi indeterminati , par lingual , par gustatorium , great sub-lingual by different authors, and gustatory nerve and lingual nerve (by Winslow). It

590-521: Is no known ganglion of the accessory nerve. The cranial part of the accessory nerve sends occasional branches to the superior ganglion of the vagus nerve. The cranial nerves provide motor and sensory supply mainly to the structures within the head and neck. The sensory supply includes both "general" sensation such as temperature and touch, and "special" senses such as taste , vision , smell , balance and hearing . The vagus nerve (X) provides sensory and autonomic (parasympathetic) supply to structures in

649-484: Is on the opposite side to the origin of the nerve, this is known as a contralateral function. Grossly , all cranial nerves have a nucleus . With the exception of the olfactory nerve (I) and optic nerve (II), all the nuclei are present in the brainstem. The midbrain has the nuclei of the oculomotor nerve (III) and trochlear nerve (IV); the pons has the nuclei of the trigeminal nerve (V), abducens nerve (VI), facial nerve (VII) and vestibulocochlear nerve (VIII); and

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708-458: Is that part of a somite that forms the muscles of the animal. Each myotome divides into an epaxial part ( epimere ), at the back, and a hypaxial part ( hypomere ) at the front. The myoblasts from the hypaxial division form the muscles of the thoracic and anterior abdominal walls. The epaxial muscle mass loses its segmental character to form the extensor muscles of the neck and trunk of mammals. In fishes, salamanders, caecilians, and reptiles,

767-480: The FDA ) may be offered the hypoglossal nerve stimulator as an alternative. The purpose of the hypoglossal nerve stimulator is to relieve tongue base obstruction during sleep by stimulating the tongue to protrude during inspiration (i.e., inhale). In this procedure, an electrical stimulator lead is placed around branches of the hypoglossal nerve that control tongue protrusion (e.g., genioglossus ) via an incision in

826-470: The cell bodies of neurons in the nerves that are outside of the brain. These ganglia are both parasympathetic and sensory ganglia. The sensory ganglia of the cranial nerves, directly correspond to the dorsal root ganglia of spinal nerves and are known as cranial nerve ganglia . Sensory ganglia exist for nerves with sensory function: V, VII, VIII, IX, X. There are also a number of parasympathetic cranial nerve ganglia . Sympathetic ganglia supplying

885-421: The digastric muscle . It then loops around a branch of the occipital artery and travels forward into the region beneath the mandible. The hypoglossal nerve moves forward lateral to the hyoglossus and medial to the stylohyoid muscles and lingual nerve . It continues deep to the genioglossus muscle and continues forward to the tip of the tongue. It distributes branches to the intrinsic and extrinsic muscle of

944-425: The hypoglossal canal and down through the neck, and eventually passes up again over the tongue muscles it supplies into the tongue. The nerve is involved in controlling tongue movements required for speech and swallowing , including sticking out the tongue and moving it from side to side. Damage to the nerve or the neural pathways which control it can affect the ability of the tongue to move and its appearance, with

1003-410: The hypoglossal nerve (XII). Cranial nerves are generally named according to their structure or function. For example, the olfactory nerve (I) supplies smell, and the facial nerve (VII) supplies the muscles of the face. Because Latin was the lingua franca of the study of anatomy when the nerves were first documented, recorded, and discussed, many nerves maintain Latin or Greek names, including

1062-454: The medulla has the nuclei of the glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI) and hypoglossal nerve (XII). The olfactory nerve (I) emerges from the olfactory bulb , and depending slightly on division the optic nerve (II) is considered to emerge from the lateral geniculate nuclei . Because each nerve may have several functions, the nerve fibres that make up the nerve may collect in more than one nucleus . For example,

1121-416: The medulla . The olfactory nerve (I) and optic nerve (II) emerge separately. The olfactory nerves emerge from the olfactory bulbs on either side of the crista galli , a bony projection below the frontal lobe , and the optic nerves (II) emerge from the lateral colliculus, swellings on either side of the temporal lobes of the brain. The cranial nerves give rise to a number of ganglia , collections of

1180-412: The nerves that emerge directly from the brain (including the brainstem ), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck , including the special senses of vision , taste , smell , and hearing . The cranial nerves emerge from the central nervous system above

1239-466: The vagus nerve . The hypoglossal nerve is of a general somatic efferent (GSE) type. These muscles are involved in moving and manipulating the tongue. The left and right genioglossus muscles in particular are responsible for protruding the tongue. The muscles, attached to the underside of the top and back parts of the tongue, cause the tongue to protrude and deviate towards the opposite side. The hypoglossal nerve also supplies movements including clearing

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1298-430: The affected genioglossus muscle, and will occur without fasciculations or wasting, with speech difficulties more evident. Damage to the hypoglossal nucleus will lead to wasting of muscles of the tongue and deviation towards the affected side when it is stuck out. This is because of the weaker genioglossal muscle. The hypoglossal nerve may be connected ( anastomosed ) to the facial nerve to attempt to restore function when

1357-521: The anterior-posterior axis through specifying the pre-somitic mesoderm before somitogenesis occurs. After somites are made, their identity as a whole has already been determined, as is shown by the fact that transplantation of somites from one region to a completely different region results in the formation of structures usually observed in the original region. In contrast, the cells within each somite retain plasticity (the ability to form any kind of structure) until relatively late in somitic development. In

1416-407: The body musculature remains segmented as in the embryo, though it often becomes folded and overlapping, with epaxial and hypaxial masses divided into several distinct muscle groups. The sclerotome (or cutis plate ) forms the vertebrae and the rib cartilage and part of the occipital bone; the myotome forms the musculature of the back, the ribs and the limbs; the syndetome forms the tendons and

1475-427: The boundaries of somites. EPHB2 is also important for boundaries. Fibronectin and N-cadherin are key to the mesenchymal–epithelial transition process in the developing embryo. The process is probably regulated by paraxis and MESP2. In turn, MESP2 is regulated by Notch signaling. Paraxis is regulated by processes involving the cytoskeleton . The Hox genes specify somites as a whole based on their position along

1534-459: The brain and brainstem, from front to back. The terminal nerves (0), olfactory nerves (I) and optic nerves (II) emerge from the cerebrum , and the remaining ten pairs arise from the brainstem, which is the lower part of the brain. The cranial nerves are considered components of the peripheral nervous system (PNS), although on a structural level the olfactory (I), optic (II), and trigeminal (V) nerves are more accurately considered part of

1593-411: The brain, as, when viewing the forebrain and brainstem from below, they are often visible in their numeric order. For example, the olfactory nerves (I) and optic nerves (II) arise from the base of the forebrain , and the other nerves, III to XII, arise from the brainstem. Cranial nerves have paths within and outside the skull . The paths within the skull are called "intracranial" and the paths outside

1652-554: The caudal half of the somite. Notch activation turns on LFNG which in turn inhibits the Notch receptor. Notch activation also turns on the HES1 gene which inactivates LFNG, re-enabling the Notch receptor, and thus accounting for the oscillating clock model. MESP2 induces the EPHA4 gene, which causes repulsive interaction that separates somites by causing segmentation. EPHA4 is restricted to

1711-584: The central nervous system (CNS). The cranial nerves are in contrast to spinal nerves , which emerge from segments of the spinal cord . Most typically, humans are considered to have twelve pairs of cranial nerves (I–XII), with the terminal nerve (0) more recently canonized. The nerves are: the olfactory nerve (I), the optic nerve (II), oculomotor nerve (III), trochlear nerve (IV), trigeminal nerve (V), abducens nerve (VI), facial nerve (VII), vestibulocochlear nerve (VIII), glossopharyngeal nerve (IX), vagus nerve (X), accessory nerve (XI), and

1770-430: The contribution of two specialized embryonic cell populations, cranial neural crest and ectodermal placodes. The components of the sensory nervous system of the head are derived from the neural crest and from an embryonic cell population developing in close proximity, the cranial sensory placodes (the olfactory, lens, otic, trigeminal, epibranchial and paratympanic placodes). The dual origin cranial nerves are summarized in

1829-414: The dermatome forms the skin on the back. In addition, the somites specify the migration paths of neural crest cells and the axons of spinal nerves . From their initial location within the somite, the sclerotome cells migrate medially towards the notochord . These cells meet the sclerotome cells from the other side to form the vertebral body. The lower half of one sclerotome fuses with the upper half of

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1888-428: The developing vertebrate embryo , somites split to form dermatomes, skeletal muscle (myotomes), tendons and cartilage (syndetomes) and bone (sclerotomes). Because the sclerotome differentiates before the dermatome and the myotome, the term dermomyotome refers to the combined dermatome and myotome before they separate out. The dermatome is the dorsal portion of the paraxial mesoderm somite which gives rise to

1947-595: The facial nerve is damaged. Attempts at repair by either wholly or partially connecting nerve fibres from the hypoglossal nerve to the facial nerve may be used when there is focal facial nerve damage (for example, from trauma or cancer). The hypoglossal nerve has also been clinically implicated in the treatment of obstructive sleep apnea . Certain patients with obstructive sleep apnea who are deemed eligible candidates (e.g., failed continuous positive airway pressure therapy, underwent appropriate testing with drug induced sleep endoscopy , and meet other criteria as outlined by

2006-1110: The following table: Contributions of neural crest cells and placodes to ganglia and cranial nerves (Ensheating glia of olfactory nerves) (m) (mix) (mix) -Inferior: geniculate, general and special afferent -Sphenopalatine, visceral efferent -Submandibular, visceral efferent -1st epibranchial placode (geniculate) -Hindbrain NCCs (2nd PA) -Hindbrain NCCs (2nd PA) (s) (mix) -Inferior, petrosal, general and special afferent -Otic, visceral efferent -2nd epibranchial placode (petrosal) -Hindbrain NCCs (from r6 into 3rd PA) (mix) Superior laryngeal branch; and recurrent laryngeal branch -Inferior: nodose, general and special afferent -Vagal: parasympathetic, visceral efferent -Hindbrain NCCs (4th& 6th PA); 3rd (nodose) and 4th epibranchial placodes -Hindbrain NCCs (4th & 6th PA) (m) Abbreviations: CN, cranial nerve; m, purely motor nerve; mix, mixed nerve (sensory and motor); NC, neural crest; PA, pharyngeal (branchial) arch; r, rhombomere; s, purely sensory nerve. * There

2065-407: The front of the medulla , the bottom part of the brainstem , in the anterolateral sulcus which separates the olive and the pyramid . The nerve passes through the subarachnoid space and pierces the dura mater near the hypoglossal canal , an opening in the occipital bone of the skull. After emerging from the hypoglossal canal, the hypoglossal nerve gives off a meningeal branch and picks up

2124-415: The head and neck reside in the upper regions of the sympathetic trunk , and do not belong to the cranial nerves. The ganglion of the sensory nerves, which are similar in structure to the dorsal root ganglion of the spinal cord , include: Additional ganglia for nerves with parasympathetic function exist, and include the ciliary ganglion of the oculomotor nerve (III), the pterygopalatine ganglion of

2183-466: The left and right hypoglossal nerves may occur with damage to the facial and trigeminal nerves as a result of damage from a clot following arteriosclerosis of the vertebrobasilar artery . Such a stroke may result in tight oral musculature, and difficulty speaking, eating and chewing. Progressive bulbar palsy , a form of motor neuron disease , is associated with combined lesions of the hypoglossal nucleus and nucleus ambiguus with wasting ( atrophy ) of

2242-422: The level of the first vertebra of the vertebral column . Each cranial nerve is paired and is present on both sides. There are conventionally twelve pairs of cranial nerves, which are described with Roman numerals I–XII. Some considered there to be thirteen pairs of cranial nerves, including the non-paired cranial nerve zero . The numbering of the cranial nerves is based on the order in which they emerge from

2301-636: The maxillary nerve (V2), the submandibular ganglion of the lingual nerve , a branch of the facial nerve (VII), and the otic ganglion of the glossopharyngeal nerve (IX). After emerging from the brain, the cranial nerves travel within the skull , and some must leave it in order to reach their destinations. Often the nerves pass through holes in the skull, called foramina , as they travel to their destinations. Other nerves pass through bony canals, longer pathways enclosed by bone. These foramina and canals may contain more than one cranial nerve and may also contain blood vessels. The cranial nerves are formed from

2360-409: The most common sources of damage being injury from trauma or surgery, and motor neuron disease . The first recorded description of the nerve was by Herophilos in the third century BC. The name hypoglossus springs from the fact that its passage is below the tongue , from hypo ( Greek : "under" ) and glossa ( Greek : "tongue" ). The hypoglossal nerve arises as a number of small rootlets from

2419-415: The motor nerves of the pons and medulla. This may cause difficulty with tongue movements, speech, chewing and swallowing caused by dysfunction of several cranial nerve nuclei. Motor neuron disease is the most common disease affecting the hypoglossal nerve. The hypoglossal nerve is tested by examining the tongue and its movements. At rest, if the nerve is injured a tongue may appear to have the appearance of

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2478-528: The mouth of saliva and other involuntary activities. The hypoglossal nucleus interacts with the reticular formation , involved in the control of several reflexive or automatic motions, and several corticonuclear originating fibers supply innervation aiding in unconscious movements relating to speech and articulation. Reports of damage to the hypoglossal nerve are rare. The most common causes of injury in one case series were compression by tumours and gunshot wounds. A wide variety of other causes can lead to damage of

2537-433: The neck and also to most of the organs in the chest and abdomen. The terminal nerve (0) may not have a role in humans, although it has been implicated in hormonal responses to smell, sexual response and mate selection. The olfactory nerve (I) conveys information giving rise to the sense of smell. Somite#Myotome The word somite is sometimes also used in place of the word metamere . In this definition,

2596-412: The neck. A sensor lead is then placed in the chest between the ribs in the layer between the internal intercostal muscles and external intercostal muscles . The stimulator and sensory lead are then connected via a tunneled wire to an implantable pulse generator. When turned on during sleep, the sensory lead in the chest detects the respiratory cycle. During inspiration (i.e., inhale), an electrical signal

2655-454: The nerve. These include surgical damage, medullary stroke, multiple sclerosis, Guillain-Barre syndrome, infection, sarcoidosis, and presence of an ectatic vessel in the hypoglossal canal. Damage can be on one or both sides, which will affect symptoms that the damage causes. Because of the close proximity of the nerve to other structures including nerves, arteries, and veins, it is rare for the nerve to be damaged in isolation. For example, damage to

2714-494: The notochord. The paraxial mesoderm is initially called the "segmental plate" in the chick embryo or the "unsegmented mesoderm" in other vertebrates. As the primitive streak regresses and neural folds gather (to eventually become the neural tube ), the paraxial mesoderm separates into blocks called somites. The pre-somitic mesoderm commits to the somitic fate before mesoderm becomes capable of forming somites. The cells within each somite are specified based on their location within

2773-424: The position of damage in this pathway. If the damage is to the nerve itself (a lower motor neuron lesion ), the tongue will curve toward the damaged side, owing to weakness of the genioglossus muscle of affected side which action is to deviate the tongue in the contralateral side . If the damage is to the nerve pathway (an upper motor neuron lesion ) the tongue will curve away from the side of damage, due to action of

2832-423: The skin ( dermis ). In the human embryo, it arises in the third week of embryogenesis . It is formed when a dermomyotome (the remaining part of the somite left when the sclerotome migrates), splits to form the dermatome and the myotome. The dermatomes contribute to the skin, fat and connective tissue of the neck and of the trunk, though most of the skin is derived from lateral plate mesoderm . The myotome

2891-399: The skull are called "extracranial". There are many holes in the skull called "foramina" by which the nerves can exit the skull. All cranial nerves are paired , which means they occur on both the right and left sides of the body. The muscle, skin, or additional function supplied by a nerve, on the same side of the body as the side it originates from, is an ipsilateral function. If the function

2950-417: The somite is a homologously -paired structure in an animal body plan , such as is visible in annelids and arthropods . The mesoderm forms at the same time as the other two germ layers , the ectoderm and endoderm . The mesoderm at either side of the neural tube is called paraxial mesoderm . It is distinct from the mesoderm underneath the neural tube, which is called the chordamesoderm that becomes

3009-425: The somite. Additionally, they retain the ability to become any kind of somite-derived structure until relatively late in the process of somitogenesis . The development of the somites depends on a clock mechanism as described by the clock and wavefront model . In one description of the model, oscillating Notch and Wnt signals provide the clock. The wave is a gradient of the fibroblast growth factor protein that

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3068-451: The somites, as the cell fates have been determined prior to somitogenesis. Somite formation can be induced by Noggin -secreting cells. The number of somites is species dependent and independent of embryo size (for example, if modified via surgery or genetic engineering). Chicken embryos have 50 somites; mice have 65, while snakes have 500. As cells within the paraxial mesoderm begin to come together, they are termed somitomeres , indicating

3127-434: The tongue for generation (i.e., lateral approximants , dental stops , alveolar stops , velar nasals , rhotic consonants etc.). Tongue strength may be tested by poking the tongue against the inside of their cheek, while an examiner feels or presses from the cheek. The hypoglossal nerve carries lower motor neurons that synapse with upper motor neurons at the hypoglossal nucleus . Symptoms related to damage will depend on

3186-453: The tongue innervates as it passes in this direction, and supplies several muscles (hyoglossus, genioglossus and styloglossus) that it passes. The rootlets of the hypoglossal nerve arise from the hypoglossal nucleus near the bottom of the brain stem . The hypoglossal nucleus receives input from both the motor cortices but the contralateral input is dominant; innervation of the tongue is essentially lateralized. Signals from muscle spindles on

3245-408: The tongue or lap ping water, decreased tongue strength, and generally cause deviation away from the affected side initially, and then to the affected side as contractures develop. The evolutionary origins of the nerve have been explored through studies of the nerve in rodents and reptiles. The nerve is regarded as arising evolutionarily from nerves of the cervical spine, which has been incorporated into

3304-409: The tongue travel through the hypoglossal nerve, moving onto the lingual nerve which synapses on the trigeminal mesencephalic nucleus . Neurons of the hypoglossal nucleus are derived from the basal plate of the embryonic medulla oblongata . The musculature they supply develops as the hypoglossal cord from the myotomes of the first four pairs of occipital somites. The nerve is first visible as

3363-476: The trigeminal nerve (V), which has a sensory and a motor role, has at least four nuclei . With the exception of the olfactory nerve (I) and optic nerve (II), the cranial nerves emerge from the brainstem . The oculomotor nerve (III) and trochlear nerve (IV) emerge from the midbrain , the trigeminal (V), abducens (VI), facial (VII) and vestibulocochlear (VIII) from the pons , and the glossopharyngeal (IX), vagus (X), accessory (XI) and hypoglossal (XII) emerge from

3422-449: The trochlear nerve (IV), named according to its structure, as it supplies a muscle that attaches to a pulley ( Greek : trochlea ). The trigeminal nerve (V) is named in accordance with its three components ( Latin : trigeminus meaning triplets ), and the vagus nerve (X) is named for its wandering course ( Latin : vagus ). Cranial nerves are numbered based on their position from front to back ( rostral-caudal ) of their position on

3481-472: Was listed in 1778 as nerve hypoglossum magnum by Soemmering. It was then named as the great hypoglossal nerve by Cuvier in 1800 as a translation of Winslow and finally named in English by Knox in 1832. The hypoglossal nerve is one of twelve cranial nerves found in amniotes including reptiles , mammals and birds. As with humans, damage to the nerve or nerve pathway will result in difficulties moving

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