cranial nerves

There are twelve pairs of cranial nerves; they are attached to the brain and are transmitted through foramina in the base of the cranium. The different pairs are named from before backward as follows:

1st. Olfactory, 2d. Optic, 3d. Oculomotor, 4th. Trochlear, 5th. Trigeminal, 6th. Abducent, 7th. Facial with (13th Intermediate), 8th. Vestibulocochlear, 9th. Glossopharyngeal, 10th. Vagus, 11th. Accessory, 12th. Hypoglossal

The area of attachment of a cranial nerve to the surface of the brain is termed its superficial or apparent origin. The fibers of the nerve can be traced into the substance of the brain to a special nucleus of gray substance. The motor or efferent cranial nerves arise within the brain from groups of nerve cells which constitute their nuclei of origin.

 The sensory or afferent cranial nerves arise from groups of nerve cells outside the brain; these nerve cells may be grouped to form ganglia on the trunks of the nerves or may be situated in peripheral sensory organs such as the nose and eye. The central processes of these cells run into the brain, and there end by arborizing around nerve cells, which are grouped to form nuclei of termination. The nuclei of origin of the motor nerves and the nuclei of termination of the sensory nerves are brought into relationship with the cerebral cortex, the former through the geniculate fibers of the internal capsule, the latter through the lemniscus. The geniculate fibers arise from the cells of the motor area of the cortex, and, after crossing the middle line, end by arborizing around the cells of the nuclei of origin of the motor cranial nerves. On the other hand, fibers arise from the cells of the nuclei of termination of the sensory nerves, and after crossing to the opposite side, join the lemniscus, and thus connect these nuclei, directly or indirectly, with the cerebral cortex.

The Olfactory Nerves

The olfactory nerves or nerves of smell are distributed to the mucous membrane of the olfactory region of the nasal cavity: this region comprises the superior nasal concha, and the corresponding part of the nasal septum.

The nerves originate from the central or deep processes of the olfactory cells of the nasal mucous membrane. They form a plexiform net-work in the mucous membrane, and are then collected into about twenty branches, which pierce the cribriform plate of the ethmoid bone in two groups, a lateral and a medial group, and end in the glomeruli of the olfactory bulb. Each branch receives tubular sheaths from the dura mater and pia mater, the former being lost in the periosteum of the nose, the latter in the neurolemma of the nerve.

The olfactory nerves are non-medullated, and consist of axis-cylinders surrounded by nucleated sheaths, in which, however, there are fewer nuclei than are found in the sheaths of ordinary non-medullated nerve fibers.

The olfactory center in the cortex is generally associated with the rhinencephalon.

The olfactary nerves are developed from the cells of the ectoderm which lines the olfactory pits; these cells undergo proliferation and give rise to what are termed the olfactory cells of the nose. The axons of the olfactory cells grow into the overlying olfactory bulb and form the olfactory nerves.

The Optic Nerve (N. Opticus) The optic nerve, or nerve of sight consists mainly of fibers derived from the ganglionic cells of the retina. These axons terminate in arborizations around the cells in the lateral geniculate body, pulvinar, and superior colliculus which constitute the lower or primary visual centers. From the cells of the lateral geniculate body and the pulvinar fibers pass to the cortical visual center, situated in the cuneus and in the neighborhood of the calcarine fissure. A few fibers of the optic nerve, of small caliber, pass from the primary centers to the retina and are supposed to govern chemical changes in the retina and also the movements of some of its elements (pigment cells and cones). There are also a few fine fibers, afferent fibers, extending from the retina to the brain, that are supposed to be concerned in pupillary reflexes.

The optic nerve is peculiar in that its fibers and ganglion cells are probably third in the series of neurons from the receptors to the brain. Consequently the optic nerve corresponds rather to a tract of fibers within the brain than to the other cranial nerves. Its fibers pass backward and medialward through the orbit and optic foramen to the optic commissure where they partially decussate. The mixed fibers from the two nerves are continued in the optic tracts, the primary visual centers of the brain.

The orbital portion of the optic nerve is from 20 mm. to 30 mm. in length and has a slightly sinuous course to allow for movements of the eyeball. It is invested by an outer sheath of dura mater and an inner sheath from the arachnoid which are attached to the sclera around the area where the nerve fibers pierce the choroid and sclera of the bulb. A little behind the bulb of the eye the central artery of the retina with its accompanying vein perforates the optic nerve, and runs within it to the retina. As the nerve enters the optic foramen its dural sheath becomes continuous with that lining the orbit and the optic foramen. In the optic foramen the ophthalmic artery lies below and to its outer side. The intercranial portion of the optic nerve is about 10 mm. in length.

The Optic Chiasma (chiasma opticum), somewhat quadrilateral in form, rests upon the tuberculum sellж and on the anterior part of the diaphragma sellж. It is in relation, above, with the lamina terminalis; behind, with the tuber cinereum; on either side, with the anterior perforated substance. Within the chiasma, the optic nerves undergo a partial decussation. The fibers forming the medial part of each tract and posterior part of the chiasma have no connection with the optic nerves. They simply cross in the chiasma, and connect the medial geniculate bodies of the two sides; they form the commissure of Gudden. The remaining and principal part of the chiasma consists of two sets of fibers, crossed and uncrossed. The crossed fibers which are the more numerous, occupy the central part of the chiasma, and pass from the optic nerve of one side to the optic tract of the other, decussating in the chiasma with similar fibers of the opposite optic nerve. The uncrossed fibers occupy the lateral part of the chiasma, and pass from the nerve of one side into the tract of the same side.

The crossed fibers of the optic nerve tend to occupy the medial side of the nerve and the uncrossed fibers the lateral side. In the optic tract, however, the fibers are much more intermingled.

The Optic Tract passes backward and outward from the optic chiasma over the tuber cinereum and anterior perforated space to the cerebral peduncle and winds obliquely across its under surface. Its fibers terminate in the lateral geniculate body, the pulvinar and the superior colliculus. It is adherent to the tuber cinereum and the cerebral peduncle as it passes over them. In the region of the lateral geniculate body it splits into two bands. The medial and smaller one is a part of the commissure of Gudden and ends in the medial geniculate body.

From its mode of development, and from its structure, the optic nerve must be regarded as a prolongation of the brain substance, rather than as an ordinary cerebrospinal nerve. As it passes from the brain it receives sheaths from the three cerebral membranes, a perineural sheath from the pia mater, an intermediate sheath from the arachnoid, and an outer sheath from the dura mater, which is also connected with the periosteum as it passes through the optic foramen. These sheaths are separated from each other by cavities which communicate with the subdural and subarachnoid cavities respectively. The innermost or perineural sheath sends a process around the arteria centralis retinж into the interior of the nerve, and enters intimately into its structure.

The Oculomotor Nerve (N. Oculomotorius)

The oculomotor nerve supplies somatic motor fibers to all the ocular muscles, except the Obliquus superior and Rectus lateralis; it also supplies through its connections with the ciliary ganglion, sympathetic motor fibers to the Sphincter pupillж and the Ciliaris muscles.

The fibers of the oculomotor nerve arise from a nucleus which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From this nucleus the fibers pass forward through the tegmentum, the red nucleus, and the medial part of the substantia nigra, forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the cerebral peduncle.

The nucleus of the oculomotor nerve does not consist of a continuous column of cells, but is broken up into a number of smaller nuclei, which are arranged in two groups, anterior and posterior. Those of the posterior group are six in number, five of which are symmetrical on the two sides of the middle line, while the sixth is centrally placed and is common to the nerves of both sides. The anterior group consists of two nuclei, an antero-medial and an antero-lateral.

The nucleus of the oculomotor nerve, considered from a physiological standpoint, can be subdivided into several smaller groups of cells, each group controlling a particular muscle.

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 and posterior cerebral arteries, and then pierces the dura mater in front of and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli. It runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic, and a communicating branch from the ophthalmic division of the trigeminal. It then divides into two branches, which enter the orbit through the superior orbital fissure, between the two heads of the Rectus lateralis. Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, while the nasociliary nerve is placed between its two rami.

The superior ramus, the smaller, passes medialward over the optic nerve, and supplies the Rectus superior and Levator palpebrж superioris. The inferior ramus, the larger, divides into three branches. One passes beneath the optic nerve to the Rectus medialis; another, to the Rectus inferior; the third and longest runs forward between the Recti inferior and lateralis to the Obliquus inferior. From the last a short thick branch is given off to the lower part of the ciliary ganglion, and forms its short root. All these branches enter the muscles on their ocular surfaces, with the exception of the nerve to the Obliquus inferior, which enters the muscle at its posterior border.

The Trochlear Nerve (N. Trochlearis; Fourth Nerve)

The trochlear nerve the smallest of the cranial nerves, supplies the Obliquus superior oculi.

It arises from a nucleus situated in the floor of the cerebral aqueduct, opposite the upper part of the inferior colliculus. From its origin it runs downward through the tegmentum, and then turns backward into the upper part of the anterior medullary velum. Here it decussates with its fellow of the opposite side and emerges from the surface of the velum at the side of the frenulum veli, immediately behind the inferior colliculus.

The nerve is directed across the superior cerebellar peduncle, and then winds forward around the cerebral peduncle, immediately above the pons, pierces the dura mater in the free border of the tentorium cerebelli, just behind, and lateral to, the posterior clinoid process, and passes forward in the lateral wall of the cavernous sinus, between the oculomotor nerve and the ophthalmic division of the trigeminal. It crosses the oculomotor nerve, and enters the orbit through the superior orbital fissure. It now becomes the highest of all the nerves, and lies medial to the frontal nerve. In the orbit it passes medialward, above the origin of the Levator palpebrж superioris, and finally enters the orbital surface of the Obliquus superior.

In the lateral wall of the cavernous sinus the trochlear nerve forms communications with the ophthalmic division of the trigeminal and with the cavernous plexus of the sympathetic. In the superior orbital fissure it occasionally gives off a branch to the lacrimal nerve. It gives off a recurrent branch which passes backward between the layers of the tentorium cerebelli and divides into two or three filaments which may be traced as far as the wall of the transverse sinus.

Innervating of the Extrinsic ocular muscles subdivide into recti (straight) and oblique:

The Trigeminal Nerve (N. Trigeminus)

Trigeminal nerve, the 5th cranial nerve, has motor nucleus and mesencephalic, pontine, spinal sensory nuclei. They localised in pons (rhomboid fossa), mesencephalon and spinal cord. Nerve starts from brain by sensory rootlet and motor rootlet between pons and middle cerebellar pedunculi. Sensory rootlet represents by central process of sensory cells, which lie in trigeminal ganglion (Gasser`s) on top of pyramide of temporal bone. This ganglion is contained in trigeminal cavity (Меckel`s) which is formed by dura mater. Motor rootlet represents by axons from motor cells (motor nucleus).

Trigeminal nerve passes from skull by three divisions:

1.     Ophthalmic nerve, sensory, exits  from skull through the superior orbital fissura;

2.     Maxillary nerve, sensory, exits  from skull through the rotundum foramen;

3.     Mandibular nerve, mixed, exits from skull through the ovale foramen.

5.1 Ophthalmic nerve fossa subdivides in orbital into frontal nerve, lacrimal nerve and nasociliary nerve. Nasociliary nerve passes on superomedial wall of orbite and under block innervating medial eye corner and nose. Sensory long ciliary nerves pass to the coats of the eyeball, short ciliary nerves pass through the ciliary ganglion and carry parasympathetic and sympathetic fibres for eyeball with all its  tissues and muscles (sphincter pupillae, dilator pupillae and ciliary muscle). Posterior and anterior ethmoidal nerves pass through the posterior and anterior ethmoidal foramen. They innervate mucous membrane of ethmoidal cells (air sinus) and anterior part of nose cavity.

Frontal nerve passes on middle part of upper wall of orbite and passes on forehead skin over supraorbital and frontal notches by three branches, innervating forehead skin and top eyelid. Lacrimal nerve passes on upper-lateral wall of orbite, transfixes a lacrimal gland, innervating it. Passing out from gland, it innervates the skin of lateral eye corner. Postganglionic and parasympathetic fibres from pterygopalatine ganglion (which pass with zygomatic nerve) pass to lacrimal nerve and provide a secretory innervation of the lacrimal gland.

5.2 Maxillary nerve passes through the rotundum foramen and reaches the pterygopalatine fossa, where ramifies on three branches: infraorbital nerve, zygomatic nerve and ganglionic branches to pterygopalatine ganglion.

 Infraorbital nerve passes through the inferior orbital fissura enters into orbite, where lies on its lower wall, passes in infraorbital fissura and infraorbital sulcus and canal. Nerve passes into canine fossa, forming ‘pes anserinus minor’. There are inferior palpebral, external nasal and superior labial nerves that innervate skin from medial eye corner to mouth corner. Superior alveolar nerves (posterior, middle and inferior) start from infraorbital nerve in maxilla. They innervate mucous membrane of the maxillary (Haymori) sinus and form superior dental plexus. The last gives off the superior dental nerves and superior gingival branches of the upper jaw.

Zygomatic nerve passes through the inferior orbital fissura entering orbite. Then it passes into zygomaticoorbital foramen and divided into zygomaticofacial and zygomaticotemporal sensory branches for skin of face and temporal region. Zygomatic nerve carries postganglionic parasympathetic fibres from pterygopalatine ganglion and gives off them to lacrimal nerve. Parasympathetic fibres provide secretory innervation of the lacrimal gland.

The ganglionic branches start from maxillary nerve and pass to pterygopalatine ganglion. Postganglionic branches include greater palatine nerve and lesser palatine nerve that pass through the greater palatine canal and lesser palatine foramens, innervating mucous membrane of the hard and soft palatine. The posterior nasal (medial and lateral) nerves pass through the sphenopalatine foramen pass into nasal cavity, where innervate mucous membrane of the nasal cavity. Nasopalatine nerve (Scarp’) start from the nasal branches and reach the mucous membrane of the hard palatine through the incisive canal. Postganglionic parasympathetic fibres from pterygopalatine ganglion are in composition of these nerves.

5.3 Mandibular nerve carries both the motor and sensory fibres. After passing out from ovale foramen mandibular nerve gives off the motor branches that innervate all 4 masticatory muscles, also velli palatine tensor muscle and nerve tensor of tympanic membrane muscle. Sensory branches of the mandibular nerve: buccal nerve, auriculotemporal nerve, lingual nerve infeior alveolar nerve and meningeal branches.

Buccal nerve transfixes a buccinator muscle and innervates mucous membrane of the cheek and also mouth corner skin.

Auriculotemporal nerve begins by two rootlets that envelop a middle meningeal artery, and then unite into one trunk, which transfixes parotid gland, innervating it and skin of temporal area, also, the auricle. Postganglionic parasympathetic fibres from otic ganglion pass in composition of this nerve, which provide a secretory innervation of parotid gland.

Lingual nerve passes on internal surface of lower jaw under mucous membrane of the mouth cavity and enters into lower part of tongue, providing a general sensory innervation of the anterior 2/3 part and sensory innervation sublingual and submandibular salivary glands. Chorda tympani (from 7th cranial nerve), which contains the gustatory (tasting) and secretory (parasympathetic) fibres. Gustatory fibres innervate of tasting buds on mucous membrane of the anterior 2/3 part of the tongue, and secretory (parasympathetic) enter in to submandibular and sublingual parasympatheticих ganglia. The postganglionic fibres from these ganglia provide a secretory innervation the same name - submandibular and sublingual salivary glands.

Inferior alveolar nerve (mixed) has a motor branches that supply mylo-hyoid muscle and anterior belly of the digastric muscle. The sensory fibres enter into mandibular channel, where form inferior dental plexus, branches innervate the teeth and gums of lower jaw. From canal these fibres are passing out from bone as a mental nerve, which terminates in skin of lower lip and chin.

Trigeminal Nerve Reflexes.—Pains referred to various branches of the trigeminal nerve are of very frequent occurrence, and should always lead to a careful examination in order to discover a local cause. As a general rule the diffusion of pain over the various branches of the nerve is at first confined to one only of the main divisions, and the search for the causative lesion should always commence with a thorough examination of all those parts which are supplied by that division; although in severe cases pain may radiate over the branches of the other main divisions. The commonest example of this condition is the neuralgia which is so often associated with dental caries—here, although the tooth itself may not appear to be painful, the most distressing referred pains may be experienced, and these are at once relieved by treatment directed to the affected tooth.

Many other examples of trigeminal reflexes could be quoted, but it will be sufficient to mention the more common ones. Dealing with the ophthalmic nerve, severe supraorbital pain is commonly associated with acute glaucoma or with disease of the frontal or ethmoidal air cells. Malignant growths or empyema of the maxillary antrum, or unhealthy conditions about the inferior conchж or the septum of the nose, are often found giving rise to “second division” neuralgia, and should be always looked for in the absence of dental disease in the maxilla.

It is on the mandibular nerve, however, that some of the most striking reflexes are seen. It is quite common to meet with patients who complain of pain in the ear, in whom there is no sign of aural disease, and the cause is usually to be found in a carious tooth in the mandible. Moreover, with an ulcer or cancer of the tongue, often the first pain to be experienced is one which radiates to the ear and temporal fossa, over the distribution of the auriculotemporal nerve.

The Abducent Nerve (N. Abducens; Sixth Nerve)

The abducent nerve supplies the Rectus lateralis oculi. Its fibers arise from a small nucleus situated in the upper part of the rhomboid fossa, close to the middle line and beneath the colliculus facialis. They pass downward and forward through the pons, and emerge in the furrow between the lower border of the pons and the upper end of the pyramid of the medulla oblongata. From the nucleus of the sixth nerve, fibers are said to pass through the medial longitudinal fasciculus to the oculomotor nerve of the opposite side, along which they are carried to the Rectus medialis. The Rectus lateralis of one eye and the Rectus medialis of the other may therefore be said to receive their nerves from the same nucleus.

The nerve pierces the dura mater on the dorsum sellae of the sphenoid, runs through a notch in the bone below the posterior clinoid process, and passes forward through the cavernous sinus, on the lateral side of the internal carotid artery. It enters the orbit through the superior orbital fissure, above the ophthalmic vein, from which it is separated by a lamina of dura mater. It then passes between the two heads of the Rectus lateralis, and enters the ocular surface of that muscle. The abducent nerve is joined by several filaments from the carotid and cavernous plexuses, and by one from the ophthalmic nerve. The oculomotor, trochlear, ophthalmic, and abducent nerves bear certain relations to each other in the cavernous sinus, at the superior orbital fissure, and in the cavity of the orbit, as follows: In the cavernous sinus, the oculomotor, trochlear, and ophthalmic nerves are placed in the lateral wall of the sinus, in the order given, from above downward. The abducent nerve lies at the lateral side of the internal carotid artery. As these nerves pass forward to the superior orbital fissure, the oculomotor and ophthalmic divide into branches, and the abducent nerve approaches the others; so that their relative positions are considerably changed.

In the superior orbital fissure, the trochlear nerve and the frontal and lacrimal divisions of the ophthalmic lie in this order from the medial to the lateral side upon the same plane; they enter the cavity of the orbit above the muscles. The remaining nerves enter the orbit between the two heads of the Rectus lateralis. The superior division of the oculomotor is the highest of these; beneath this lies the nasociliary branch of the ophthalmic; then the inferior division of the oculomotor; and the abducent lowest of all.   

In the orbit, the trochlear, frontal, and lacrimal nerves lie immediately beneath the periosteum, the trochlear nerve resting on the Obliquus superior, the frontal on the Levator palpebrae superioris, and the lacrimal on the Rectus lateralis. The superior division of the oculomotor nerve lies immediately beneath the Rectus superior, while the nasociliary nerve crosses the optic nerve to reach the medial wall of the orbit. Beneath these is the optic nerve, surrounded in front by the ciliary nerves, and having the ciliary ganglion on its lateral side, between it and the Rectus lateralis. Below the optic nerve are the inferior division of the oculomotor, and the abducent, the latter lying on the medial surface of the Rectus lateralis.

VII Facial nerve consists of 1- proper facial nerve, which has fibers starting from motor nucleus in depth of facial colliculus in rhomboid fossa, and 2- intermediate nerve, which has a fibers of sensory nucleus of solitarius tract and parasympathetic - superior salivatory nucleus.

Facial nerve passes through facial canal, gives off motor branch for stapedius muscle, then exits from skull through the stylomastoid foramen and innervates posterior auricular, stylohyoid muscles and posterior belly of digastric muscle. Facial nerve enters into thickness of parotid salivary glands (but does not innervate it!) and forms there parotid plexus. Last gives off the motor branches which innervate facial expression (mimetic) muscles. There are: temporal branches (supply auricular, orbicularis oculi and occipitofrontalis muscles), zygomatic branches (they supply zygomatic major and orbicularis oculi muscles), buccal branches (supply zygomatic major and minor, levator labii superioris, buccinator, orbicularis oris, nasalis,  and risorius muscles), marginal mandibulae branch (supplies depressor anguli oris and depressor labii inferioris, mentalis muscles) and cervical branch (for the platisma).

Intermediate nerve has two divisions: Nervus petrosus major and Chorda tympani.

Greater petrosal nerve (preganglionic secretory fibers to the lacrimal glands, nasal glands and palatal glands) separates off from the geniculate ganglion, extends through the hiatus of the canal for the greater petrosal nerve, across the foramen lacerum and finally through the pterygoid canal to the pterygopalatine ganglion.

Chorda tympani carries preganglionic secretory fibers to the submandibular and sublingual glands and taste fibers to the anterior two third of the tongue. Taste (sensory) fibers contain peripheral axons of cells localized in geniculate ganglion. The central process of neurocytes of this ganglion terminate in nucleus of solitarius tract. Chorda tympani passes through the petrotympanic fissura and joints the lingual nerve (from the Vth cranial nerve), then its branches reach the tongue and parasympathetic submandibular and sublingual ganglia for innervating the same names salivary glands.

The Vestibulocochlear Nerve (Eighth Nerve)

The vestibulocochlear nerve consists of two distinct sets of fibers which differ in their peripheral endings, central connections, functions, and time of medullation. It is soft in texture and devoid of neurilemma. Cochlear Nerve, the nerve of hearing, arises from bipolar cells in the spiral ganglion of the cochlea, situated near the inner edge of the osseous spiral lamina. The peripheral fibers pass to the organ of Corti. The central ones pass down the modiolus and then through the foramina of the tractus spiralis foraminosus or through the foramen centrale into the lateral or outer end of the internal auditory meatus. The nerve passes along the internal auditory meatus with the vestibular nerve and across the subarachnoid space, just above the flocculus, almost directly medialward toward the inferior peduncle to terminate in the cochlear nucleus. The cochlear nerve is placed lateral to the vestibular root. Its fibers end in two nuclei: one, the accessory nucleus, lies immediately in front of the inferior peduncle; the other, the tuberculum acusticum, somewhat lateral to it.  The striae medullares (striae acusticae) are the axons of the cells of the tuberculum acusticum. They pass over the inferior peduncle, and across the rhomboid fossa to the median sulcus. Here they dip into the substance of the pons, to end around the cells of the superior olivary nuclei of both sides. There are, however, other fibers, and these are both direct and crossed, which pass into the lateral lemniscus. The cells of the accessory nucleus give origin to fibers which run transversely in the pons and constitute the trapezium. Of the trapezoid fibers some end around the cells of the superior olivary nucleus or of the trapezoid nucleus of the same or opposite side, while others, crossed or uncrossed, pass directly into the lateral lemniscus. If the further connections of the cochlear nerve of one side, say the left, be considered, it is found that they lie lateral to the main sensory tract, the lemniscus, and are therefore termed the lateral lemniscus. The fibers comprising the left lateral lemniscus arise in the superior olivary and trapezoid nuclei of the same or opposite side, while others are the uninterrupted fibers already alluded to, and these are either crossed or uncrossed, the former being the axons of the cells of the right accessory nucleus or of the cells of the right tuberculum acusticum, while the latter are derived from the cells of the left nuclei. In the upper part of the lateral lemniscus there is a collection of nerve cells, the nucleus of the lateral lemniscus, around the cells of which some of the fibers arborize and from the cells of which axons originate to continue upward the tract of the lateral lemniscus. The ultimate ending of the left lateral lemniscus is partly in the opposite medial geniculate body, and partly in the inferior colliculi. From the cells of these bodies new fibers arise and ascend in the occipital part of the internal capsule to reach the posterior three-fifths of the left superior temporal gyrus and the transverse temporal gyri. Vestibular Nerve, the nerve of equilibration, arises from bipolar cells in the vestibular ganglion, ganglion of Scarpa, which is situated in the upper part of the outer end of the internal auditory meatus. The peripheral fibers divide into three branches: the superior branch passes through the foramina in the area vestibularis superior and ends in the utricle and in the ampullae of the superior and lateral semicircular ducts; the fibers of the inferior branch traverse the foramina in the area vestibularis inferior and end in the saccule; the posterior branch runs through the foramen singulare and supplies the ampulla of the posterior semicircular duct. 

IX Glossopharyngeal nerve is mixed nerve, which has a nucleus ambiguous (motor), nucleus of the tractus solitarius (sensory) and inferior salivatory nucleus (parasympathetic) in rhomboid fossa. Sensory fibers start from a superior and inferior ganglia in region of the jugular foramen. Glossopharyngeal nerve reaches the tongue root, where divides by final branches rr. linguales, that innervating mucous membrane the posterior third of the tongue.

Glossopharyngeal nerve gives off the following branches:

1.   Tympanic nerve (mixed) passes through tympanic canalicule and enters into tympanic cavity. Here its sensory branches together with caroticotympanic nerves (sympathetic) form tympanic plexus which innervate mucous membrane of the tympanic cavity and auditory tube (r. tubarius). The parasympathetic preganglionic fibers start from inferior salivatory nucleus, exite from tympanic cavity through hyatus nervi petrosi minoris as lesser petrosal nerve. Last passes in sulcus and enters into otic ganglion. Postganglionic fibres provide a secretory innervation of parotid salivary glands.

2.   Pharyngeal branches pass to lateral wall of the pharynx, where together with branches of vagus nerve and sympathetic trunk form pharyngeal plexus. Last provides innervating of the muscles and mucous membrane of the throat.

3.   Tonsillar branches pass to mucous membrane of the palatine tonsils and palatal arches.

4.   Branch of stylopharyngeal muscle.

5.   Branch of carotid sinus, innervating the receptors of carotid glomus and sinus.

6.   Communicating branch with the auricular branch of vagus nerve.

X Vagus nerve (mixed) contains motor fibers which start from nucleus ambiguus, parasympathetic (preganglionic) fibers form dorsal nucleus and sensory fibers from superior and inferior ganglia in jugular foramen.

*                    Cranial part of vagus nerve gives off the following branches:

Meningeal branch which starts from superior ganglion and passes to cranial dura mater in posterior cranial fossa;

Auricular branch, which starts from superior ganglion, passes over mastoid canalicule of temporal bone and innervates the skin of external surface of auricle and posterior wall of external acoustic meatus.

*                    Cervical part of vagus nerve gives off:

Pharyngeal branches with branches of Glossopharyngeal nerve and sympathetic trunk form pharyngeal plexus, that innervates mucous membrane and muscles of the throat (superior and middle constrictors; levator veli palatini, palatopharyngeus and palatoglossus, uvulae muscles).

Superior cervical cardiac branches pass downward along common carotid artery and  communicate with sympathetic nerves, enter into cardiac plexus and supply the heart (sensory and parasympathetic innervating).

Superior laryngeal nerve originate from inferior ganglion and carry sensory, motor and parasympathetic preganglionic fibers. Motor fibers of the external branch innervate cricothyroid and inferior constrictor muscles, sensory fibers (internal branch) supply mucous membrane of the larynx over vocal fold, mucous membrane of the epiglottis and tongue root.

Recurrent laryngeal nerve passes upward between esophagus and trachea and sends a numerous twigs. Inferior laryngeal nerve supplies mucous membrane of the larynx below vocal fold and the rest of muscles (thyroarytenoid, lateral and posterior cricoarytenoid, transverse and oblique arytenoid, vocalis). Tracheal, esophageal and inferior cervical cardiac branches supply internal organs.

*                    Thoracic part of vagus nerve gives off:

Thoracic cardiac branches which pass to cardiac plexus;

Bronchial branches with sympathetic nerves form pulmonary plexus. Last enters in lungs with bronchi.

Esophageal branches form esophageal plexus round this organ.

Abdominal part of vagus nerve is represented by anterior and posterior vagal trunks, which originate from esophageal plexus. Anterior vagal trunk located on front surface of the stomach and gives branches gives off the anterior gastric and hepatic branches. Posterior vagal trunk supplies back gastric wall, and gives off coeliac branches to reach coeliac plexus. Then fibers of vagus nerve with sympathetic fibers supply the liver, spleen, pancreas, kidneys, small and large intestine (including a upper department of descending colon).

The Accessory Nerve (N. Accessorius; Eleventh Nerve)

The accessory nerve consists of two parts: a cranial and a spinal. 1) The Cranial Part (ramus internus; accessory portion) is the smaller of the two. Its fibers arise from the cells of the nucleus ambiguus and emerge as four or five delicate rootlets from the side of the medulla oblongata, below the roots of the vagus. It runs lateralward to the jugular foramen, where it interchanges fibers with the spinal portion or becomes united to it for a short distance; here it is also connected by one or two filaments with the jugular ganglion of the vagus. It then passes through the jugular foramen, separates from the spinal portion and is continued over the surface of the ganglion nodosum of the vagus, to the surface of which it is adherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. Through the pharyngeal branch it probably supplies the Musculus uvulae and Levator veli palatini. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the recurrent nerve and probably also with the cardiac nerves. 2) The Spinal Part (ramus externus; spinal portion) is firm in texture, and its fibers arise from the motor cells in the lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve. Passing through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves; enters the skull through the foramen magnum, and is then directed to the jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but separated from it by a fold of the arachnoid. In the jugular foramen, it receives one or two filaments from the cranial part of the nerve, or else joins it for a short distance and then separates from it again. As its exit from the jugular foramen, it runs backward in front of the internal jugular vein in 66.6 per cent. of cases, and behind in it 33.3 per cent. (Tandler). The nerve then descends obliquely behind the Digastricus and Stylohyoideus to the upper part of the Sternocleidomastoideus; it pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the second cervical nerve. In the posterior triangle it unites with the second and third cervical nerves, while beneath the Trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibers are distributed to the muscle. 

The Hypoglossal Nerve (N. Hypoglossus; Twelfth Nerve)

The hypoglossal nerve is the motor nerve of the tongue. Its fibers arise from the cells of the hypoglossal nucleus, which is an upward prolongation of the base of the anterior column of gray substance of the medulla spinalis. This nucleus is about 2 cm. in length, and its upper part corresponds with the trigonum hypoglossi, or lower portion of the medial eminence of the rhomboid fossa. The lower part of the nucleus extends downward into the closed part of the medulla oblongata, and there lies in relation to the ventro-lateral aspect of the central canal. The fibers run forward through the medulla oblongata, and emerge in the antero-lateral sulcus between the pyramid and the olive. The rootlets of this nerve are collected into two bundles, which perforate the dura mater separately, opposite the hypoglossal canal in the occipital bone, and unite together after their passage through it; in some cases the canal is divided into two by a small bony spicule. The nerve descends almost vertically to a point corresponding with the angle of the mandible. It is at first deeply seated beneath the internal carotid artery and internal jugular vein, and intimately connected with the vagus nerve; it then passes forward between the vein and artery, and lower down in the neck becomes superficial below the Digastricus. The nerve then loops around the occipital artery, and crosses the external carotid and lingual arteries below the tendon of the Digastricus. It passes beneath the tendon of the Digastricus, the Stylohyoideus, and the Mylohyoideus, lying between the last-named muscle and the Hyoglossus, and communicates at the anterior border of the Hyoglossus with the lingual nerve; it is then continued forward in the fibers of the Genioglossus as far as the tip of the tongue, distributing branches to its muscular substance.   

The descending ramus (ramus descendens; descendens hypoglossi), long and slender, quits the hypoglossal where it turns around the occipital artery and descends in front of or in the sheath of the carotid vessels; it gives a branch to the superior belly of the Omohyoideus, and then joins the communicantes cervicales from the second and third cervical nerves; just below the middle of the neck, to form a loop, the ansa cervicalis. From the convexity of this loop branches pass to supply the Sternohyoideus, the Sternothyreoideus, and the inferior belly of the Omohyoideus. According to Arnold, another filament descends in front of the vessels into the thorax, and joins the cardiac and phrenic nerves. The Thyrohyoid Branch (ramus thyreohyoideus) arises from the hypoglossal near the posterior border of the hyoglossus; it runs obliquely across the greater cornu of the hyoid bone, and supplies the Thyreohyoideus muscle. The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Geniohyoideus, and Genioglossus. At the under surface of the tongue numerous slender branches pass upward into the substance of the organ to supply its intrinsic muscles.

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