Introduction of cranial nerves:-
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Olfactory nerve:-
It is a nerve of special sense for smell.
It consists of fibres which are the axons of the olfactory cells in the olfactory part of the nasal mucous membrane.
The fibres are non-medullated and are collected into small bundles enclosed in sheaths furnished by the meninges of the brain; pass through the cribriform plate of the ethmoid and join the convex face of the olfactory bulb.
Optic nerve:-
It is a nerve of sense for sight. This nerve is composed of medullated fibres devoid of neurilemma which are axons of the ganglion cells of retina.
The fibres converge within the eyeball at the optic papilla, where they form the optic nerve.
Then it pierces through the choroid and sclera, emerges from the inferio-lateral quadrant of the eye and passes backward and inward to the optic foramen.
On entering the cranium the two nerves decussate at the base of the brain and form the optic chiasma or commissure.
From the optic commissure, the optic tract passes into the lateral geniculate body and anterior quadrigeminal body.
The sheath of the nerve is formed by the prolongation of the meninges of the brain.
Occulo-motor nerve:-
It is the motor nerve to the muscles of the eyeball.
It arises from the ventromedial aspect of the cerebral peduncle turns sharply outward and forward, crossing over the posterior primary branch of the emergent artery of the rete mirabile cerebri through the cavernous sinus along with the ophthalmic and the sixth cranial nerves.
It leaves the cranium through the foramen orbito rotundum, enters the orbit, pierces the periorbita and divides into dorsal and ventral branches.
The dorsal branch supplies medial rectus, ventral rectus and ventral oblique muscles and also conveys parasympathetic efferents to the ciliary ganglion that after relay in the ganglion are distributed to the ciliary muscle and constrictor pupillae of iris.
Trochlear nerve:-
It is the motor nerve to the superior oblique muscle of the eyeball. It is the finest of the cranial nerves.
It arises from the dorsal aspect of midbrain close to and behind the corpora quadrigemina where the anterior cerebellar peduncle enters the midbrain.
The nerve passes forward and outward along the lateral border of the fifth cranial nerve, through the cavernous sinus and leaves the cranium through the foramen orbitorotundum and supplies the superior oblique muscle of the eyeball.
Trigeminal nerve:-
It is a mixed nerve. It is the largest of the cranial nerves.
It is connected to the lateral aspect of the pons by a large sensory root and a small motor root; the sensory root forms the semilunar ganglion under which the motor root passes forward.
The convex face of the ganglion gives off three branches, the ophthalmic, maxillary and mandibular nerves.
Opthalmic nerve
The ophthalmic nerve is purely sensory and leaves the cranium through the foramen orbitorotundum and divides into frontal, lacrimal and naso ciliary branches.
The frontal nerve emerges from the orbit through the supraorbital canal and supplies the upper eyelid and the skin.
The lacrimal nerve supplies the lacrimal gland, skin over the temporal fossa, frontal sinus and a long cornual branch that passes below the lateral border of the body of the frontal bone along with the branches of superficial temporal artery and vein to supply the corium of the horn.
The naso ciliary nerve runs toward the ethmoidal foramen where it divides into the ethmoidal nerve and the infra-trochlear nerve.
The ethmoidal nerve passes through the ethmoidal foramen into cranial cavity and leaves it through the cribriform plate of ethmoid and supplies the nasal mucous membrane. ( View the branches of Nerves to the facial region )
The infratrochlear nerve runs towards the medial canthus and supplies the conjunctiva, lacrimal ducts, lacrimal sac and the third eyelid.
Maxillary nerve
The maxillary nerve is the largest of the three branches and is also purely sensory like the ophthalmic.
It emerges out of the cranium through the foramen orbitorotundum runs forward in the pterygopalatine fossa and gives off the following branches.
zygomatic or orbital branch which runs to the lateral canthus and supplies lower eyelid and skin.
sphenopalatine nerve that is given off in the pterygopalatine fossa, bears the sphenopalatine ganglion. It divides into
posterior nasal nerve passes through sphenopalatine foramen to supply the nasal mucous membrane.
the greater or anterior palatine which runs through the palatine canal and groove to supply hard palate and gums.
the lesser or posterior palatine which passes downward to supply the soft palate.
Then the maxillary nerve continues as the infraorbital nerve, which passes through the infraorbital canal, gives off dental branches to the upper cheek teeth, alveolar periosteum and gums, emerges out of the infraorbital foramen and divides into nasal and labial branches to supply nostril and upper lip, respectively.
Mandibular nerve:-
The mandibular nerve is a mixed nerve. Its sensory root arises from the semilunar ganglion soon after it is joined by the motor root. The motor fibres supply only the muscles of mastication. The mixed nerve thus formed leaves the cranium through the foramen ovale, runs downwards between the pterygoids, enters the mandibular foramen of the mandible, runs through the inferior dental canal and gains exit at the mental foramen. Before entering the mandibular canal. It gives off a number of branches in its course.
Masseteric nerve: Passes through the mandibular notch enters the deep face of the masseter and supplies it.
Deep temporal: To supply temporalis muscle.
Buccinator nerve: Passes downward and forward on the medial aspect of temporo mandibular articulation, runs downward in the submucous tissue of the cheek and supplies mucosa of the cheek.
Pterygoid nerve: Arises in common with the preceding and supplies the pterygoid muscles and branches to tensor palati and tensor tympani.
Mylohyoid nerve: Passes downward to supply the mylohyoideus muscle and also the anterior belly of digastricus.
Superficial temporal nerve: Passes backward to the posterior border of the mandible a little below its neck turns outward and then forward under the parotid lymph gland and divides into transverse facial nerve, supplying skin of the cheek and a ventral branch which unites with the dorsal buccal division of the facial nerve. It also gives a branch to parotid salivary gland that conveys postganglionic secretomotor fibres from otic ganglion.
Lingual nerve:Runs downwards and forward between the ramus of the mandible and medial pterygoid muscle to the root of the tongue, where it divides into a superficial branch, which accompanies the mandibular duct on the deep face of the sublingual gland and supplies the mucous membrane of the tongue and floor of the mouth and a deep branch, which runs between hyoglossus to the tip of the tongue. It supplies the mucous membrane of the anterior two third of the tongue.
In the course of the mandibular nerve through the mandibular canal,it supplies dental branches to lower cheek teeth, and sends a branch through the incisor canal to supply lower incisors. After emerging out of the mental foramen, the nerve divides into a number of labial filaments to supply the lower lip.
Abducent nerve:-
This is a motor nerve.
It arises just behind the pons, lateral to the inferior pyramid of the medulla.
It passes forward across the pons, pierces the dura and accompanies the nerves in the cavernous sinus.
It leaves the cranium through the foramen orbitorotundum reaches the orbit and supplies the lateral rectus and retractor oculi.
Facial nerve:-
This is the seventh cranial nerve and is a mixed nerve. It arises from the lateral part of the corpus trapezoideum immediately behind the pons.
It passes outwards across the fifth cranial nerve and in front of the eighth cranial nerve and enters the internal auditory meatus with it. At the bottom of this meatus the two nerves get separated and the facial nerve enters the facial canal passes in it at first, directed outward, then curves backward and ventrally into the posterior wall of the tympanum to end at the stylo mastoid foramen.
The bent part of the nerve is the genu and bears at its highest point the geniculate ganglion. After its emergence through the stylo mastoid foramen, the nerve passes forward and outward under the parotid salivary gland where it terminates into dorsal and ventral buccal nerves.
The following branches are detached within the facial canal.
Great superficial Petrosal nerve: It arises from the geniculate ganglion in the facial canal, passes backward, reaches the cranial cavity through the internal auditory meatus, emerges through the foramen lacerum and is continued as the nerve of pterygoid canal to sphenopalatine ganglion. This nerve conveys parasympathetic (preganglionic) fibres to the lacrimal gland and glands of nasal mucosa that after relay in the spheno palatine ganglion, are conveyed to these structures in the respective branches of the trigeminal nerve.
Stapedial nerve: It is detached as it turns in the facial canal. It supplies stapedius muscle in the middle ear.
Chorda tympani nerve: It is given off a little below the preceding. It enters the tympanic cavity, passes across it and then descends and emerges through the petrotympanic fissure, gains the company of the lingual branch of the fifth nerve and supplies gustatory fibers to the anterior two third of the mucous membrane of the tongue. It also supplies secreto motor fibres to the submaxillary and sublingual salivary glands through the submandibular ganglion. After emergence through the stylomastoid foramen, the facial nerve gives off the following branches:
Posterior auricular nerve: Which runs upward and backward under the parotid gland and supplies posterior auricular muscles.
Internal or deep auricular nerve: Passes through a foramen in the conchal cartilage and supplies skin on the internal surface of the external ear.
Digastric branch: Descends below under the cover of parotid gland and supplies the posterior belly of digastricus, occipitohyoideus and stylohyoideus.
Auriculo palpebral nerve: Passes upward under the parotid gland and divides into anterior auricular branch supplying anterior auricular muscles and palpebral or temporal nerve which runs forward to supply orbicularis oculi, corrugator supercilli and levator nasolabialis.
A cervical branch that passes under parotid gland and parotidoauricularis muscle downward and backward and anastomoses with cutaneous branches of cervical spinal nerves.
Of the two terminal branches, the dorsal buccal nerve passes forward on the upper part of masseter and is joined by a branch from the superficial temporal division of the trigeminal nerve. It continues forward under zygomaticus and along the ventral border of dilator naris lateralis and ramifies on the muscles of the upper lip and nostril. It also supplies zygomaticus, malaris and buccinator. It anastomoses with ventral buccal nerve and receives a communicating branch along the anterior border of masseter.
The ventral buccal nerve passes downward obliquely across the lower part of masseter, runs forward along the ventral border of depressor labii inferioris. It supplies the muscles of the lower lip.
Acoustic or auditory nerve:-
This is the nerve of sense of hearing and equilibrium.
It arises from the medulla at the lateral part of the corpus trapezoideum just behind the preceding nerve.
It has two roots vestibular and cochlear.
The nerve passes outward along with the facial to the internal auditory meatus. Here it divides into two branches an upper vestibular and the lower cochlear nerves.
In the internal auditory meatus this nerve presents the vestibular ganglion.
The peripheral processes of the cells of the ganglion are then distributed to the maculae of the utricle and the saccule, and the cristae ampullaris of the semicircular canals of the internal ear.
The cochlear nerve detaches a filament to the saccule and passes through the modiolus and joins the spiral ganglion.
The peripheral processes of the cells of the ganglion run in the lamina spiralis and are distributed to the organ of corti in the cochlea.
Glossopharyngeal nerve:-
This is a mixed nerve. It is attached to the lateral part of the medulla at its anterior aspect by several filaments ventral to the restiform body and are separated by a narrow interval from the preceding nerve in front and the vagus behind.
The nerve fibres converge laterally into a bundle that pierces the dura, emerges through the foramen lacerum and then bears a ganglion called petrosal ganglion. It then curves forward and downward, behind the great cornu of the hyoid divided into the pharyngeal and the lingual branches. Its branches are
The tympanic nerve arises from the petrosal ganglion passes upward between the petrous and tympanic parts of the temporal bone to reach the cavity of tympanum. Here it forms along with branches from the plexus of the sympathetic, the tympanic plexus. From the plexus, branches pass to the mucous membrane of the tympanum and pharyngotympanic tube. The continuation of the nerve from the plexus joins a branch from the geniculate ganglion. The lesser superficial petrosal nerve conveys parasympathetic fibres supplying the parotid salivary gland, after relay in the otic ganglion.
a small branch to supply stylopharyngeus muscle.
Pharyngeal branch with which branches of vagus and sympathetic forms the pharyngeal plexus and supplies the mucous membrane of the pharynx.
The lingual branch supplies gustatory and ordinary sensory fibres to the posterior one third of the tongue. It also supplies soft palate, tonsil and isthmus faucium.
Vegus nerve:-
This is a mixed nerve.
It is the longest and the most widely distributed of all the cranial nerves.
It is attached to the lateral aspect of the medulla oblongata by several filaments, which arise in a series with those of the glossopharyngeal in front and the spinal accessory behind.
The bundles converge to form a trunk that passes outward pierces the dura and emerges out of the cranium through the foramen lacerum. In the foramen, it bears the jugular ganglion. Beyond this, it runs backward and downward with the eleventh cranial nerve. Then the two nerves separate and the twelfth cranial nerve passes between them.
It descends along with cervical sympathetic to form a common vago-sympathetic cord on the dorsal part of the carotid sheath above carotid artery and descends deeply in the jugular furrow and enters the thorax.
Collateral branches
The right vagus crosses under the right brachial artery across the trachea, reaches the oesophagus behind the aortic arch and divides into dorsal and ventral branches.
The left vagus enters the thoracic cavity, passes under the arch of the left brachial artery and the root of the aorta, reaches the left lung and then across the surface of the oesophagus, divides into dorsal and ventral branches.
The two dorsal and the two ventral branches of the vagi unite forming the two trunks dorsal and ventral oesophageal continuations of the vagi on the respective faces of the oesophagus, which pass through the diaphragm into the abdominal cavity to supply the abdominal organs.
The auricular branch from the jugular ganglion enters the facial canal, emerges out at the stylomastoid foramen passes through the foramen in the conchal cartilage and supplies branches to the lining membrane of the external ear.
The pharyngeal branch along with the pharyngeal branch of glossopharyngeal and the sympathetic fibres form a plexus from which motor fibres are supplied to the pharyngeal constrictors, muscles of soft palate except tensor palati.
The anterior laryngeal nerve presents at its origin the ganglion nodosum. It arises at about the level of the division of the carotid artery, supplies sensory branches to the mucous membrane of the larynx and an external laryngeal branch for the cricothyroid muscle.
In the neck, the vagus gives off branches to trachea and oesophagus.
In the thoracic cavity, the vagus gives off the following branches
Cardiac branches to the heart.
Pulmonary branches to the lungs.
The posterior or recurrent laryngeal nerve: It arises from the vagus at different levels on the two sides. The right is in advance of the left at the posterior border of the first rib, gives off sensory branches to the trachea and oesophagus, leaves the thorax, passes up the neck in the jugular furrow inside the carotid sheath below the common carotid artery and gives off branches to all the laryngeal muscles except the cricothyroid.
The left recurrent laryngeal arises at the level of the base of the heart, winds round the right face of the aortic arch, passes forward, gives off sensory branches to the trachea and oesophagus, leaves the thorax, passes in the neck deeply in the jugular furrow along the ventral face of the oesophagus which separates it from the carotid sheath. It reaches the larynx and is distributed to the muscles of the larynx as on the right side.
In the abdominal cavity, the dorsal and ventral oesophageal trunks are distributed as follows:
The dorsal trunk gives off
Branch accompanying omaso abomasal artery and its divisions and supplies omasum and abomasum.
Branches which accompany splenic, right and left ruminal arteries, supply corresponding organs
Branches which accompany the divisions of anterior mesenteric artery, supply the small and large intestines except the terminal colon and rectum
Branches to kidney.
The ventral trunk passes on the right face of reticulum and terminates on the parietal surface of the abomasum. It gives off the pyloric branch which passes along the lesser omentum to supply the liver, first and second parts of duodenum and pyloric part of abomasum.
Spinal accesory nerve:-
This is a motor nerve. It has two roots, the medullary and spinal.
The medullary root arises from the lateral aspect of the medulla by several rootlets behind and in a series with those of the vagus.
The spinal root arises from the cervical part of the spinal cord by a series of fasciculi arising from the first five segments that unite to form a trunk and this root enters the cranium through the foramen magnum and joins the medullary root.
The nerve thus formed leaves the cranial cavity along with the vagus, through the foramen lacerum and passes downward and backward, leaves the company of the vagus passes under the deep face of mandibular salivary gland passes backward winding round the wing of atlas and divides into dorsal and ventral branches.
The dorsal branch passes backward under brachiocephalicus and ramifies on the deep face of trapezius.
The ventral branch passes downward across the oesophagus and trachea and supplies sternocephalicus.
Hypoglossal nerve:-
It is the motor nerve to the muscles of the tongue. Its fibres arise from the ventral face of the medulla oblongata in a series lateral to the posterior half of the pyramid.
The filaments converge into three or four bundles that perforate the dura and unite to form the nerve.
The nerve then emerges through the hypoglossal foramen runs downward and backward related to the atlantooccipital articulation.
It passes between the tenth and the eleventh nerves, bends downward and forward, passes over the glossopharyngeal nerve and the great cornu of the hyoid bone.
It gains the lateral face of the hyoglossus muscle and divides into branches to supply the muscles of the tongue.
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