Cranial nerves

There are twelve pairs of cranial nerves; they’re hooked up to the mind and are transmitted by way of foramina within the base of the skull. The totally different pairs are named from earlier than backward as follows:

1st. Olfactory, second. Optic, 3d. Oculomotor, 4th. Trochlear, fifth. Trigeminal, sixth. Abducent, seventh. Facial with (13^th Intermediate), eighth. Vestibulocochlear, ninth. Glossopharyngeal, tenth. Vagus, eleventh. Accent, twelfth. Hypoglossal

The realm of attachment of a cranial nerve to the floor of the mind is termed its superficial or obvious origin. The fibers of the nerve could be traced into the substance of the mind to a particular nucleus of grey substance. The motor or efferent cranial nerves come up inside the mind from teams of nerve cells which represent their nuclei of origin.

 The sensory or afferent cranial nerves come up from teams of nerve cells exterior the mind; these nerve cells could also be grouped to kind ganglia on the trunks of the nerves or could also be located in peripheral sensory organs such because the nostril and eye. The central processes of those cells run into the mind, and there finish by arborizing round nerve cells, that are grouped to kind nuclei of termination. The nuclei of origin of the motor nerves and the nuclei of termination of the sensory nerves are introduced into relationship with the cerebral cortex, the previous by way of the geniculate fibers of the inner capsule, the latter by way of the lemniscus. The geniculate fibers come up from the cells of the motor space of the cortex, and, after crossing the center line, finish by arborizing across the cells of the nuclei of origin of the motor cranial nerves. Alternatively, fibers come up from the cells of the nuclei of termination of the sensory nerves, and after crossing to the alternative facet, be a part of the lemniscus, and thus join these nuclei, instantly or not directly, with the cerebral cortex.

The Olfactory Nerves

The olfactory nerves or nerves of odor are distributed to the mucous membrane of the olfactory area of the nasal cavity: this area contains the superior nasal concha, and the corresponding a part of the nasal septum.

The nerves originate from the central or deep processes of the olfactory cells of the nasal mucous membrane. They kind a plexiform net-work within the mucous membrane, and are then collected into about twenty branches, which pierce the cribriform plate of the ethmoid bone in two teams, a lateral and a medial group, and finish within the glomeruli of the olfactory bulb. Every department receives tubular sheaths from the dura mater and pia mater, the previous being misplaced within the periosteum of the nostril, the latter within the neurolemma of the nerve.

The olfactory nerves are non-medullated, and encompass axis-cylinders surrounded by nucleated sheaths, by which, nevertheless, there are fewer nuclei than are discovered within the sheaths of abnormal non-medullated nerve fibers.

The olfactory heart within the cortex is mostly related to the rhinencephalon.

The olfactary nerves are developed from the cells of the ectoderm which strains the olfactory pits; these cells bear proliferation and provides rise to what are termed the olfactory cells of the nostril. The axons of the olfactory cells develop into the overlying olfactory bulb and kind the olfactory nerves.

The Optic Nerve (N. Opticus) The optic nerve, or nerve of sight consists primarily of fibers derived from the ganglionic cells of the retina. These axons terminate in arborizations across the cells within the lateral geniculate physique, pulvinar, and superior colliculus which represent the decrease or major visible facilities. From the cells of the lateral geniculate physique and the pulvinar fibers move to the cortical visible heart, located within the cuneus and within the neighborhood of the calcarine fissure. Just a few fibers of the optic nerve, of small caliber, move from the first facilities to the retina and are supposed to manipulate chemical modifications within the retina and in addition the actions of a few of its components (pigment cells and cones). There are additionally a number of high quality fibers, afferent fibers, extending from the retina to the mind, which are purported to be involved in pupillary reflexes.

The optic nerve is peculiar in that its fibers and ganglion cells are most likely third within the collection of neurons from the receptors to the mind. Consequently the optic nerve corresponds quite to a tract of fibers inside the mind than to the opposite cranial nerves. Its fibers move backward and medialward by way of the orbit and optic foramen to the optic commissure the place they partially decussate. The combined fibers from the 2 nerves are continued within the optic tracts, the major visible facilities of the mind.

The orbital portion of the optic nerve is from 20 mm. to 30 mm. in size and has a barely sinuous course to permit for actions of the eyeball. It’s invested by an outer sheath of dura mater and an interior sheath from the arachnoid that are hooked up to the sclera across the space the place the nerve fibers pierce the choroid and sclera of the bulb. Slightly behind the bulb of the attention the central artery of the retina with its accompanying vein perforates the optic nerve, and runs inside it to the retina. Because the nerve enters the optic foramen its dural sheath turns into steady with that lining the orbit and the optic foramen. Within the optic foramen the ophthalmic artery lies under and to its outer facet. The intercranial portion of the optic nerve is about 10 mm. in size.

The Optic Chiasma (chiasma opticum), considerably quadrilateral in kind, rests upon the tuberculum sellж and on the anterior a part of the diaphragma sellж. It’s in relation, above, with the lamina terminalis; behind, with the tuber cinereum; on both facet, with the anterior perforated substance. Inside the chiasma, the optic nerves bear a partial decussation. The fibers forming the medial a part of every tract and posterior a part of the chiasma don’t have any reference to the optic nerves. They merely cross within the chiasma, and join the medial geniculate our bodies of the 2 sides; they kind the commissure of Gudden. The remaining and principal a part of the chiasma consists of two units of fibers, crossed and uncrossed. The crossed fibers that are the extra quite a few, occupy the central a part of the chiasma, and move from the optic nerve of 1 facet to the optic tract of the opposite, decussating within the chiasma with related fibers of the alternative optic nerve. The uncrossed fibers occupy the lateral a part of the chiasma, and move from the nerve of 1 facet into the tract of the identical facet.

The crossed fibers of the optic nerve are likely to occupy the medial facet of the nerve and the uncrossed fibers the lateral facet. Within the optic tract, nevertheless, the fibers are way more intermingled.

The Optic Tract passes backward and outward from the optic chiasma over the tuber cinereum and anterior perforated area to the cerebral peduncle and winds obliquely throughout its below floor. Its fibers terminate within the lateral geniculate physique, the pulvinar and the superior colliculus. It’s adherent to the tuber cinereum and the cerebral peduncle because it passes over them. Within the area of the lateral geniculate physique it splits into two bands. The medial and smaller one is part of the commissure of Gudden and ends within the medial geniculate physique.

From its mode of growth, and from its construction, the optic nerve have to be considered a prolongation of the mind substance, quite than as an abnormal cerebrospinal nerve. Because it passes from the mind 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 can also be related with the periosteum because it passes by way of the optic foramen. These sheaths are separated from one another by cavities which talk with the subdural and subarachnoid cavities respectively. The innermost or perineural sheath sends a course of across the arteria centralis retinж into the inside of the nerve, and enters intimately into its construction.

The Oculomotor Nerve (N. Oculomotorius)

The oculomotor nerve provides somatic motor fibers to all of the ocular muscle groups, besides the Obliquus superior and Rectus lateralis; it additionally provides by way of its connections with the ciliary ganglion, sympathetic motor fibers to the Sphincter pupillж and the Ciliaris muscle groups.

The fibers of the oculomotor nerve come up from a nucleus which lies within the grey substance of the ground of the cerebral aqueduct and extends in entrance of the aqueduct for a brief distance into the ground of the third ventricle. From this nucleus the fibers move ahead by way of the tegmentum, the purple nucleus, and the medial a part of the substantia nigra, forming a collection of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial facet of the cerebral peduncle.

The nucleus of the oculomotor nerve doesn’t encompass a steady column of cells, however is damaged up into numerous smaller nuclei, that are organized in two teams, anterior and posterior. These of the posterior group are six in quantity, 5 of that are symmetrical on the 2 sides of the center line, whereas the sixth is centrally positioned and is frequent to the nerves of each side. The anterior group consists of two nuclei, an antero-medial and an antero-lateral.

The nucleus of the oculomotor nerve, thought of from a physiological standpoint, could be subdivided into a number of smaller teams of cells, every group controlling a specific muscle.

On rising from the mind, 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, after which pierces the dura mater in entrance of and lateral to the posterior clinoid course of, passing between the free and hooked up borders of the tentorium cerebelli. It runs alongside the lateral wall of the cavernous sinus, above the opposite orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic, and a speaking department from the ophthalmic division of the trigeminal. It then divides into two branches, which enter the orbit by way of the superior orbital fissure, between the 2 heads of the Rectus lateralis. Right here the nerve is positioned under the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, whereas the nasociliary nerve is positioned between its two rami.

The superior ramus, the smaller, passes medialward over the optic nerve, and provides the Rectus superior and Levator palpebrж superioris. The inferior ramus, the bigger, divides into three branches. One passes beneath the optic nerve to the Rectus medialis; one other, to the Rectus inferior; the third and longest runs ahead between the Recti inferior and lateralis to the Obliquus inferior. From the final a brief thick department is given off to the decrease a part of the ciliary ganglion, and kinds its quick root. All these branches enter the muscle groups on their ocular surfaces, except for 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, provides the Obliquus superior oculi.

It arises from a nucleus located within the ground of the cerebral aqueduct, reverse the higher a part of the inferior colliculus. From its origin it runs downward by way of the tegmentum, after which turns backward into the higher a part of the anterior medullary velum. Right here it decussates with its fellow of the alternative facet and emerges from the floor of the velum along with the frenulum veli, instantly behind the inferior colliculus.

The nerve is directed throughout the superior cerebellar peduncle, after which winds ahead across the cerebral peduncle, instantly above the pons, pierces the dura mater within the free border of the tentorium cerebelli, simply behind, and lateral to, the posterior clinoid course of, and passes ahead within 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 by way of the superior orbital fissure. It now turns into the very best of all of the nerves, and lies medial to the frontal nerve. Within the orbit it passes medialward, above the origin of the Levator palpebrж superioris, and eventually enters the orbital floor of the Obliquus superior.

Within the lateral wall of the cavernous sinus the trochlear nerve kinds communications with the ophthalmic division of the trigeminal and with the cavernous plexus of the sympathetic. Within the superior orbital fissure it sometimes offers off a department to the lacrimal nerve. It offers off a recurrent department which passes backward between the layers of the tentorium cerebelli and divides into two or three filaments which can be traced so far as the wall of the transverse sinus.

Innervating of the Extrinsic ocular muscle groups subdivide into recti (straight) and indirect:

The Trigeminal Nerve (N. Trigeminus)

Trigeminal nerve, the 5^th cranial nerve, has motor nucleus and mesencephalic, pontine, spinal sensory nuclei. They localised in pons (rhomboid fossa), mesencephalon and spinal twine. Nerve begins from mind by sensory rootlet and motor rootlet between pons and center cerebellar pedunculi. Sensory rootlet represents by central technique of sensory cells, which lie in trigeminal ganglion (Gasser`s) on high of pyramide of temporal bone. This ganglion is contained in trigeminal cavity (Меckel`s) which is shaped by dura mater. Motor rootlet represents by axons from motor cells (motor nucleus).

Trigeminal nerve passes from cranium by three divisions:

1. Ophthalmic nerve, sensory, exits  from cranium by way of the superior orbital fissura;
2. Maxillary nerve, sensory, exits  from cranium by way of the rotundum foramen;
3. Mandibular nerve, combined, exits from cranium by way of 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 below block innervating medial eye nook and nostril. Sensory lengthy ciliary nerves move to the coats of the eyeball, quick ciliary nerves move by way of the ciliary ganglion and carry parasympathetic and sympathetic fibres for eyeball with all its  tissues and muscle groups (sphincter pupillae, dilator pupillae and ciliary muscle). Posterior and anterior ethmoidal nerves move by way of the posterior and anterior ethmoidal foramen. They innervate mucous membrane of ethmoidal cells (air sinus) and anterior a part of nostril cavity.

Frontal nerve passes on center a part of higher wall of orbite and passes on brow pores and skin over supraorbital and frontal notches by three branches, innervating brow pores and skin and high eyelid. Lacrimal nerve passes on upper-lateral wall of orbite, transfixes a lacrimal gland, innervating it. Passing out from gland, it innervates the pores and skin of lateral eye nook. Postganglionic and parasympathetic fibres from pterygopalatine ganglion (which move with zygomatic nerve) move to lacrimal nerve and supply a secretory innervation of the lacrimal gland.

5.2 Maxillary nerve passes by way of the rotundum foramen and reaches the pterygopalatine fossa, the place ramifies on three branches: infraorbital nerve, zygomatic nerve and ganglionic branches to pterygopalatine ganglion.

 Infraorbital nerve passes by way of the inferior orbital fissura enters into orbite, the place lies on its decrease wall, passes in infraorbital fissura and infraorbital sulcus and canal. Nerve passes into canine fossa, forming ‘pes anserinus minor’. There are inferior palpebral, exterior nasal and superior labial nerves that innervate pores and skin from medial eye nook to mouth nook. Superior alveolar nerves (posterior, center and inferior) begin from infraorbital nerve in maxilla. They innervate mucous membrane of the maxillary (Haymori) sinus and kind superior dental plexus. The final offers off the superior dental nerves and superior gingival branches of the higher jaw.

Zygomatic nerve passes by way of the inferior orbital fissura getting into orbite. Then it passes into zygomaticoorbital foramen and divided into zygomaticofacial and zygomaticotemporal sensory branches for pores and skin of face and temporal area. Zygomatic nerve carries postganglionic parasympathetic fibres from pterygopalatine ganglion and offers off them to lacrimal nerve. Parasympathetic fibres present secretory innervation of the lacrimal gland.

The ganglionic branches begin from maxillary nerve and move to pterygopalatine ganglion. Postganglionic branches embrace better palatine nerve and lesser palatine nerve that move by way of the better palatine canal and lesser palatine foramens, innervating mucous membrane of the arduous and tender palatine. The posterior nasal (medial and lateral) nerves move by way of the sphenopalatine foramen move into nasal cavity, the place innervate mucous membrane of the nasal cavity. Nasopalatine nerve (Scarp’) begin from the nasal branches and attain the mucous membrane of the arduous palatine by way of the incisive canal. Postganglionic parasympathetic fibres from pterygopalatine ganglion are in composition of those nerves.

5.3 Mandibular nerve carries each the motor and sensory fibres. After passing out from ovale foramen mandibular nerve offers off the motor branches that innervate all 4 masticatory muscle groups, additionally 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 in addition mouth nook pores and skin.

Auriculotemporal nerve begins by two rootlets that envelop a center meningeal artery, after which unite into one trunk, which transfixes parotid gland, innervating it and pores and skin of temporal space, additionally, the auricle. Postganglionic parasympathetic fibres from otic ganglion move in composition of this nerve, which give a secretory innervation of parotid gland.

Lingual nerve passes on inside floor of decrease jaw below mucous membrane of the mouth cavity and enters into decrease a part of tongue, offering a common sensory innervation of the anterior 2/3 half and sensory innervation sublingual and submandibular salivary glands. Chorda tympani (from seventh cranial nerve), which comprises the gustatory (tasting) and secretory (parasympathetic) fibres. Gustatory fibres innervate of tasting buds on mucous membrane of the anterior 2/3 a part of the tongue, and secretory (parasympathetic) enter in to submandibular and sublingual parasympatheticих ganglia. The postganglionic fibres from these ganglia present a secretory innervation the identical identify – submandibular and sublingual salivary glands.

Inferior alveolar nerve (combined) has a motor branches that provide mylo-hyoid muscle and anterior stomach of the digastric muscle. The sensory fibres enter into mandibular channel, the place kind inferior dental plexus, branches innervate the tooth and gums of decrease jaw. From canal these fibres are passing out from bone as a psychological nerve, which terminates in pores and skin of decrease lip and chin.

Trigeminal Nerve Reflexes.—Pains referred to numerous branches of the trigeminal nerve are of very frequent incidence, and will all the time result in a cautious examination with a purpose to uncover an area trigger. As a common rule the diffusion of ache over the assorted branches of the nerve is at first confined to 1 solely of the principle divisions, and the seek for the causative lesion ought to all the time start with an intensive examination of all these elements that are provided by that division; though in extreme circumstances ache could radiate over the branches of the opposite fundamental divisions. The most common instance of this situation is the neuralgia which is so usually related to dental caries—right here, though the tooth itself could not seem like painful, essentially the most distressing referred pains could also be skilled, and these are directly relieved by remedy directed to the affected tooth.

Many different examples of trigeminal reflexes may very well be quoted, however it will likely be enough to say the extra frequent ones. Coping with the ophthalmic nerve, extreme supraorbital ache is often related to acute glaucoma or with illness of the frontal or ethmoidal air cells. Malignant growths or empyema of the maxillary antrum, or unhealthy situations in regards to the inferior conchж or the septum of the nostril, are sometimes discovered giving rise to “second division” neuralgia, and needs to be all the time appeared for within the absence of dental illness within the maxilla.

It’s on the mandibular nerve, nevertheless, that a number of the most placing reflexes are seen. It’s fairly frequent to fulfill with sufferers who complain of ache within the ear, in whom there is no such thing as a signal of aural illness, and the trigger is normally to be present in a carious tooth within the mandible. Furthermore, with an ulcer or most cancers of the tongue, usually the primary ache to be skilled 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 provides the Rectus lateralis oculi. Its fibers come up from a small nucleus located within the higher a part of the rhomboid fossa, near the center line and beneath the colliculus facialis. They move downward and ahead by way of the pons, and emerge within the furrow between the decrease border of the pons and the higher finish of the pyramid of the medulla oblongata. From the nucleus of the sixth nerve, fibers are stated to move by way of the medial longitudinal fasciculus to the oculomotor nerve of the alternative facet, alongside which they’re carried to the Rectus medialis. The Rectus lateralis of 1 eye and the Rectus medialis of the opposite could subsequently be stated to obtain their nerves from the identical nucleus.

The nerve pierces the dura mater on the dorsum sellae of the sphenoid, runs by way of a notch within the bone under the posterior clinoid course of, and passes ahead by way of the cavernous sinus, on the lateral facet of the inner carotid artery. It enters the orbit by way of the superior orbital fissure, above the ophthalmic vein, from which it’s separated by a lamina of dura mater. It then passes between the 2 heads of the Rectus lateralis, and enters the ocular floor of that muscle. The abducent nerve is joined by a number of filaments from the carotid and cavernous plexuses, and by one from the ophthalmic nerve. The oculomotor, trochlear, ophthalmic, and abducent nerves bear sure relations to one another within the cavernous sinus, on the superior orbital fissure, and within the cavity of the orbit, as follows: Within the cavernous sinus, the oculomotor, trochlear, and ophthalmic nerves are positioned within the lateral wall of the sinus, within the order given, from above downward. The abducent nerve lies on the lateral facet of the inner carotid artery. As these nerves move ahead to the superior orbital fissure, the oculomotor and ophthalmic divide into branches, and the abducent nerve approaches the others; in order that their relative positions are significantly modified.

Within the superior orbital fissure, the trochlear nerve and the frontal and lacrimal divisions of the ophthalmic lie on this order from the medial to the lateral facet upon the identical airplane; they enter the cavity of the orbit above the muscle groups. The remaining nerves enter the orbit between the 2 heads of the Rectus lateralis. The superior division of the oculomotor is the very best of those; beneath this lies the nasociliary department of the ophthalmic; then the inferior division of the oculomotor; and the abducent lowest of all.   

Within the orbit, the trochlear, frontal, and lacrimal nerves lie instantly 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 instantly beneath the Rectus superior, whereas the nasociliary nerve crosses the optic nerve to succeed in the medial wall of the orbit. Beneath these is the optic nerve, surrounded in entrance by the ciliary nerves, and having the ciliary ganglion on its lateral facet, between it and the Rectus lateralis. Under the optic nerve are the inferior division of the oculomotor, and the abducent, the latter mendacity on the medial floor of the Rectus lateralis.

VII Facial nerve consists of 1- correct facial nerve, which has fibers ranging 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 by way of facial canal, offers off motor department for stapedius muscle, then exits from cranium by way of the stylomastoid foramen and innervates posterior auricular, stylohyoid muscle groups and posterior stomach of digastric muscle. Facial nerve enters into thickness of parotid salivary glands (however doesn’t innervate it!) and kinds there parotid plexus. Final offers off the motor branches which innervate facial features (mimetic) muscle groups. There are: temporal branches (provide auricular, orbicularis oculi and occipitofrontalis muscle groups), zygomatic branches (they provide zygomatic main and orbicularis oculi muscle groups), buccal branches (provide zygomatic main and minor, levator labii superioris, buccinator, orbicularis oris, nasalis,  and risorius muscle groups), marginal mandibulae department (provides depressor anguli oris and depressor labii inferioris, mentalis muscle groups) and cervical department (for the platisma).

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

Larger petrosal nerve (preganglionic secretory fibers to the lacrimal glands, nasal glands and palatal glands) separates off from the geniculate ganglion, extends by way of the hiatus of the canal for the better petrosal nerve, throughout the foramen lacerum and eventually by way of the pterygoid canal to the pterygopalatine ganglion.

Chorda tympani carries preganglionic secretory fibers to the submandibular and sublingual glands and style fibers to the anterior two third of the tongue. Style (sensory) fibers comprise peripheral axons of cells localized in geniculate ganglion. The central technique of neurocytes of this ganglion terminate in nucleus of solitarius tract. Chorda tympani passes by way of the petrotympanic fissura and joints the lingual nerve (from the V^th cranial nerve), then its branches attain the tongue and parasympathetic submandibular and sublingual ganglia for innervating the identical names salivary glands.

The Vestibulocochlear Nerve (Eighth Nerve)

The vestibulocochlear nerve consists of two distinct units of fibers which differ of their peripheral endings, central connections, features, and time of medullation. It’s tender in texture and devoid of neurilemma. Cochlear Nerve, the nerve of listening to, arises from bipolar cells within the spiral ganglion of the cochlea, located close to the interior fringe of the osseous spiral lamina. The peripheral fibers move to the organ of Corti. The central ones move down the modiolus after which by way of the foramina of the tractus spiralis foraminosus or by way of the foramen centrale into the lateral or outer finish of the inner auditory meatus. The nerve passes alongside the inner auditory meatus with the vestibular nerve and throughout the subarachnoid area, simply above the flocculus, virtually instantly medialward towards the inferior peduncle to terminate within the cochlear nucleus. The cochlear nerve is positioned lateral to the vestibular root. Its fibers finish in two nuclei: one, the accent nucleus, lies instantly in entrance of the inferior peduncle; the opposite, the tuberculum acusticum, considerably lateral to it.  The striae medullares (striae acusticae) are the axons of the cells of the tuberculum acusticum. They move over the inferior peduncle, and throughout the rhomboid fossa to the median sulcus. Right here they dip into the substance of the pons, to finish across the cells of the superior olivary nuclei of each side. There are, nevertheless, different fibers, and these are each direct and crossed, which move into the lateral lemniscus. The cells of the accent nucleus give origin to fibers which run transversely within the pons and represent the trapezium. Of the trapezoid fibers some finish across the cells of the superior olivary nucleus or of the trapezoid nucleus of the identical or reverse facet, whereas others, crossed or uncrossed, move instantly into the lateral lemniscus. If the additional connections of the cochlear nerve of 1 facet, say the left, be thought of, it’s discovered that they lie lateral to the principle sensory tract, the lemniscus, and are subsequently termed the lateral lemniscus. The fibers comprising the left lateral lemniscus come up within the superior olivary and trapezoid nuclei of the identical or reverse facet, whereas others are the uninterrupted fibers already alluded to, and these are both crossed or uncrossed, the previous being the axons of the cells of the fitting accent nucleus or of the cells of the fitting tuberculum acusticum, whereas the latter are derived from the cells of the left nuclei. Within the higher a part of the lateral lemniscus there’s a assortment of nerve cells, the nucleus of the lateral lemniscus, across the cells of which a number of the fibers arborize and from the cells of which axons originate to proceed upward the tract of the lateral lemniscus. The last word ending of the left lateral lemniscus is partly within the reverse medial geniculate physique, and partly within the inferior colliculi. From the cells of those our bodies new fibers come up and ascend within the occipital a part of the inner capsule to succeed in 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 within the vestibular ganglion, ganglion of Scarpa, which is located within the higher a part of the outer finish of the inner auditory meatus. The peripheral fibers divide into three branches: the superior department passes by way of the foramina within the space vestibularis superior and ends within the utricle and within the ampullae of the superior and lateral semicircular ducts; the fibers of the inferior department traverse the foramina within the space vestibularis inferior and finish within the saccule; the posterior department runs by way of the foramen singulare and provides the ampulla of the posterior semicircular duct. 

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

Glossopharyngeal nerve offers off the next branches:

1. Tympanic nerve (combined) passes by way of tympanic canalicule and enters into tympanic cavity. Right here its sensory branches along with caroticotympanic nerves (sympathetic) kind tympanic plexus which innervate mucous membrane of the tympanic cavity and auditory tube (r. tubarius). The parasympathetic preganglionic fibers begin from inferior salivatory nucleus, exite from tympanic cavity by way of hyatus nervi petrosi minoris as lesser petrosal nerve. Final passes in sulcus and enters into otic ganglion. Postganglionic fibres present a secretory innervation of parotid salivary glands.
2. Pharyngeal branches move to lateral wall of the pharynx, the place along with branches of vagus nerve and sympathetic trunk kind pharyngeal plexus. Final offers innervating of the muscle groups and mucous membrane of the throat.
3. Tonsillar branches move to mucous membrane of the palatine tonsils and palatal arches.
4. Department of stylopharyngeal muscle.
5. Department of carotid sinus, innervating the receptors of carotid glomus and sinus.
6. Speaking department with the auricular department of vagus nerve.

X Vagus nerve (combined) comprises motor fibers which begin from nucleus ambiguus, parasympathetic (preganglionic) fibers kind dorsal nucleus and sensory fibers from superior and inferior ganglia in jugular foramen.

• Cranial a part of vagus nerve offers off the next branches:

Meningeal department which begins from superior ganglion and passes to cranial dura mater in posterior cranial fossa;

Auricular department, which begins from superior ganglion, passes over mastoid canalicule of temporal bone and innervates the pores and skin of exterior floor of auricle and posterior wall of exterior acoustic meatus.

• Cervical a part of vagus nerve offers off:

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

Superior cervical cardiac branches move downwardalongcommon carotid artery and  talk with sympathetic nerves, enter into cardiac plexus and provide the guts (sensory and parasympathetic innervating).

Superior laryngeal nerve originate from inferior ganglion and carry sensory, motor and parasympathetic preganglionic fibers. Motor fibers of the exterior department innervate cricothyroid and inferior constrictor muscle groups, sensory fibers (inside department) provide 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 quite a few twigs. Inferior laryngeal nerve provides mucous membrane of the larynx under vocal fold and the remainder of muscle groups (thyroarytenoid, lateral and posterior cricoarytenoid, transverse and indirect arytenoid, vocalis). Tracheal, esophageal and inferior cervical cardiac branches provide inside organs.

• Thoracic a part of vagus nerve offers off:

Thoracic cardiac branches which move to cardiac plexus;

Bronchial branches with sympathetic nerves kind pulmonary plexus. Final enters in lungs with bronchi.

Esophageal branches kind esophageal plexus spherical this organ.

Belly a part of vagus nerve is represented by anterior and posterior vagal trunks, which originate from esophageal plexus. Anterior vagal trunk situated on entrance floor of the abdomen and offers branches offers off the anterior gastric and hepatic branches. Posterior vagal trunk provides again gastric wall, and offers off coeliac branches to succeed in coeliac plexus. Then fibers of vagus nerve with sympathetic fibers provide the liver, spleen, pancreas, kidneys, small and huge gut (together with a higher division of descending colon).

The Accent Nerve (N. Accessorius; Eleventh Nerve)

The accent nerve consists of two elements: a cranial and a spinal. 1) The Cranial Half (ramus internus; accent portion) is the smaller of the 2. Its fibers come up from the cells of the nucleus ambiguus and emerge as 4 or 5 delicate rootlets from the facet of the medulla oblongata, under the roots of the vagus. It runs lateralward to the jugular foramen, the place it interchanges fibers with the spinal portion or turns into united to it for a brief distance; right here additionally it is related by one or two filaments with the jugular ganglion of the vagus. It then passes by way of the jugular foramen, separates from the spinal portion and is sustained over the floor of the ganglion nodosum of the vagus, to the floor of which it’s adherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. By way of the pharyngeal department it most likely provides the Musculus uvulae and Levator veli palatini. Some few filaments from it are continued into the trunk of the vagus under the ganglion, to be distributed with the recurrent nerve and possibly additionally with the cardiac nerves. 2) The Spinal Half (ramus externus; spinal portion) is agency in texture, and its fibers come up from the motor cells within the lateral a part of the anterior column of the grey substance of the medulla spinalis as little as the fifth cervical nerve. Passing by way of the lateral funiculus of the medulla spinalis, they emerge on its floor and unite to kind a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves; enters the cranium by way of the foramen magnum, and is then directed to the jugular foramen, by way of which it passes, mendacity in the identical sheath of dura mater because the vagus, however separated from it by a fold of the arachnoid. Within the jugular foramen, it receives one or two filaments from the cranial a part of the nerve, or else joins it for a brief distance after which separates from it once more. As its exit from the jugular foramen, it runs backward in entrance of the inner jugular vein in 66.6 per cent. of circumstances, and behind in it 33.3 per cent. (Tandler). The nerve then descends obliquely behind the Digastricus and Stylohyoideus to the higher a part of the Sternocleidomastoideus; it pierces this muscle, and programs obliquely throughout the posterior triangle of the neck, to finish within the deep floor of the Trapezius. Because it traverses the Sternocleidomastoideus it offers a number of filaments to the muscle, and joins with branches from the second cervical nerve. Within the posterior triangle it unites with the second and third cervical nerves, whereas beneath the Trapezius it kinds 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 come up from the cells of the hypoglossal nucleus, which is an upward prolongation of the bottom of the anterior column of grey substance of the medulla spinalis. This nucleus is about 2 cm. in size, and its higher half corresponds with the trigonum hypoglossi, or decrease portion of the medial eminence of the rhomboid fossa. The decrease a part of the nucleus extends downward into the closed a part of the medulla oblongata, and there lies in relation to the ventro-lateral side of the central canal. The fibers run ahead by way of the medulla oblongata, and emerge within 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 individually, reverse the hypoglossal canal within the occipital bone, and unite collectively after their passage by way of it; in some circumstances the canal is split into two by a small bony spicule. The nerve descends virtually vertically to a degree corresponding with the angle of the mandible. It’s at first deeply seated beneath the inner carotid artery and inside jugular vein, and intimately related with the vagus nerve; it then passes ahead between the vein and artery, and decrease down within the neck turns into superficial under the Digastricus. The nerve then loops across the occipital artery, and crosses the exterior carotid and lingual arteries under the tendon of the Digastricus. It passes beneath the tendon of the Digastricus, the Stylohyoideus, and the Mylohyoideus, mendacity between the last-named muscle and the Hyoglossus, and communicates on the anterior border of the Hyoglossus with the lingual nerve; it’s then continued ahead within the fibers of the Genioglossus so far as the tip of the tongue, distributing branches to its muscular substance.   

The descending ramus (ramus descendens; descendens hypoglossi), lengthy and slender, quits the hypoglossal the place it turns across the occipital artery and descends in entrance of or within the sheath of the carotid vessels; it offers a department to the superior stomach of the Omohyoideus, after which joins the communicantes cervicales from the second and third cervical nerves; just under the center of the neck, to kind a loop, the ansa cervicalis. From the convexity of this loop branches move to provide the Sternohyoideus, the Sternothyreoideus, and the inferior stomach of the Omohyoideus. In accordance with Arnold, one other filament descends in entrance of the vessels into the thorax, and joins the cardiac and phrenic nerves. The Thyrohyoid Department (ramus thyreohyoideus) arises from the hypoglossal close to the posterior border of the hyoglossus; it runs obliquely throughout the better cornu of the hyoid bone, and provides the Thyreohyoideus muscle. The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Geniohyoideus, and Genioglossus. On the below floor of the tongue quite a few slender branches move upward into the substance of the organ to provide its intrinsic muscle groups.