Cranial nerves Cranial nerve There are 12 paired

Cranial nerves & Cranial nerve ØThere are 12, paired cranial nuclei : nerves. ØThe first 2 cranial Ns. attach directly to forebrain (frontal lobe) , while the rest attach to brain stem. ØOlfactory system is attached to forebrain and is referred to as the limbic system, / optic N. also is discribed in visual pathway. The base of the brain showing locations of cranial nerves ØCranial Ns. from 3 - 12 have nuclei (cranial N. nucluei) in the brain stem , receiving afferents Fs. Or send efferent Fs. as the cranial Ns.

Superficial attachements of Cranial ØOcculomotor & trochlear Ns. nerves : are attached to midbrain. ØTrigeminal N. is attached to antero-lateral surface of pons. ØAbducent, Facial & vestibulocochlear Ns. are lying between pons & M. O. from medial to lateral. ØHypoglossal N. is attached to antero-lateral sulcus of M. O. / but glossopharyngeal, vagus & accessory Ns. are attached to The base of the brain showing postero-lateral sulcus of M. O. locations of cranial nerves

Afferent Nerve Nuclei : ØFibres carrying general sensation from the head via trigeminal N. terminate in a large trigeminal sensory nucleus that extends the whole length of brain stem and cervical spinal cord. ØFibres carrying hearing & motion/ positional sense via vestibulo-cochlear N. terminate in cochlear & vestibular nuclei that are located in upper M. O. Dorsal aspect of brain stem showing locations of Afferent cranial N. nuclei (left) , and Efferent cranial N. nuclei (right) , in which the same colours have a common embryological origin. ØVisceral afferents carrying taste sensation via facial & glossopharyngeal Ns. , terminate in nucleus solitarius located in upper M. O.

Efferent Nerve Nuclei : ØSomatic efferent column : supplies striated Ms. in head, including : yellow colour 1 - Oculomotor nucleus. 2 -Trochlear nucleus. 3 -Abducent nucleus. 4 -Hypoglssal nucleus. ØBranchiomotor (special visceral) efferent column : supplies striated Ms. derived from branchial arches, including : orange 1 - Trigeminal motor nucleus. Nucleus ambiguus. 2 - Facial ØParasympathetic (general visceral) efferent column : supplies glands & smooth Ms. of viscera , including : pink colour 1 - 3 -

Somatic efferent Nerve Nuclei ØOculomotor nucleus : lies at the base of periaqueductal grey of midbrain at the level of superior colliculus. Its efferent Fs. run in oculomotor N. to innervate levator palpebrae superiooris + all extraocular Ms. Except L. R & S. O Ø Trochlear nucleus : lies at the ventral part of periaqueductal grey of midbrain at the level of inferior colliculus. Its efferent Fs. run in trochlear N. to innervate S. O. muscle.

Oculomotor & trochlear Nerves ØOculomotor nerve : emerges from the medial aspect of each cerebral peduncle e. g. through the interpeduncular fossa. Anterior view of midbrain Posterior view of midbrain ØTrochlear nerve : emerges from back of midbrain, caudal to inferior colliculus and then passes laterally around cerebral peduncle to appear on the anterior view of midbrain.

Somatic efferent Nerve Nuclei : ØAbducent nucleus : lies in the caudal pons , beneath floor of 4 th vent. Its efferent Fs. run in abducent N. to supply L. R. ØHypoglossal nucleus : lies in the rostral M. O. its efferent Fs. run in hypoglossal N. to supply all Ms. of tongue Except palatoglossus muscle.

Branchiomotor efferent Nerve Nuclei ØTrigeminal motor nucleus : lies in the tegmentum of the mid-pons and its motor Fs. run in mandibular branch of trigeminal N. to supply structures of 1 st pharyngeal arch as Ms. of mustication, mylohyoid, ant. belly of digastric, tensor tympani (middle ear) & tensor veli palatini. (soft palate). ØFacial motor nucleus : lies in the caudal pontine tegmentum, its motor Fs. run in facial N. to innervate Ms. of facial expression, stapedius muscle (middle ear) & other Ms. derived from 2 nd pharygeal arch (stylohyoid, post. belly of digastric). ØNucleus ambiguus : it is a long nucleus lies in M. O. , sending motor Fs. in 9 th , 10 th & cranial root of 11 th nerves to innervate Ms. of pharynx & larynx derived from 3, 4& 6

Parasympathetic efferent Nerve Nuclei : ØEdinger-Westphal nucleus lies in midbrain adjacent to oculomotor nucleus. It is the parasymp. part of oculomotor nucleus. It gives preganglionic parasymp. motor Fs. Via oculomotor N. into ciliary ganglion, which sends postganglionic Fs. to innervate sphincter pupillae & ciliary Ms. in the eye. ØSuperior salivary nucleus : lies in pontine tegmentum, it gives preganglionic Fs. Via facial N. into pterygopalatine & submandibular ganglia , which gives postganglionic Fs. to innervate lacrimal gl. , Nasal and oral M. Ms. & submandibular and sublingual salivary glands…. respictevly

Parasympathetic efferent Nerve Nuclei : ØInferior salivary nucleus : lies in pontine tegmentum, sends preganglionic Fs. Via glosso-pharyngeal N. into otic ganglion , which sends post-ganglionic Fs. to parotid gland. ØDorsal motor nucleus of vagus : lies in the rostral M. O. lateral to hypoglossal nucleus, it gives preganglionic parasymp. Fs. Via vagus N. to innervate thoracic & abdominal viscera.

Cranial Nerves : III : Oculomotor N. ØThis N. contains 2 -types of fibres : 1 - Somatic motor efferent Fs. from oculomotor nucleus to all extrinsic eye Ms. Except S. O &L. R. 2 - Preganglionic parasymp. motor Fs. from Edinger-Westphal nucleus to constrictor pupillae & ciliary muscle via postganglionic Fs. of short ciliary nerves arise from ciliary ganglion. ØThis N. lying in the lateral wall of cavernus sinus before passes to orbit through sup. orbital fissure.

Eye movements brought about by the extraocular muscles : ØOculomotor nerve supplies sup. rectus, inf. rectus , medial rectus , inferior oblique & levator palpebrae superioris, so it elevates , depresses and adducts the eyeball. ØTrochlear N. supplies S. O, it depresses eyeball down & medial ØAbducent N. supplies L. R , it abdducts eyeball.

T. S of midbrain at the level of sup. colliculus to illustrate the pathway of pupillary light reflex. ØIf the light is illuminated on one eye , it causes constriction of the pupil of the same eye due to contraction of constrictor pupillae muscle…. This is called direct light reflex. ØThe constriction of the pupil of the nonilluminated eye is called consensual (indirect) light reflex. ØDuring the visual pathway , small Fs. leave the optic tract to synape in the pretectal nucleus, which projects bilaterally Fs. to Note that pretectal area involves in mediation of pupillary light reflex. Edinger-Westphal nuclei of occulomotor , that send efferent parasympathetic Fs. Via oculomotor nerves on both sides to sphincter pupillae ms.

Accomodation Reflex : ØFixation upon a nearby object, involves contraction of ciliary muscles to increase the convexity of lens, thus focusing the image. ØIt is also accompanied by pupillary constriction due to activation of constrictor pupillae m. ØAlso, Cortico-bulbar Fs. ( visual frontal cortex) activate the parasymp. Edinger-Westphal nuclei on both sides to supply ciliary & sphincter pupillae Ms. Optic pathway and Visual reflexes (pupillary light R. + accomodation R. )

IV : Trochlear Nerve : ØThis N. carries only somatic motor efferent Fs. from the trochlear nucleus in midbrain (level of inferior colliculus) to supply the S. O. of opposite side. ØTrchlear N. , the only nerve emerges from the post. surface of brain - stem , then appears on the ventral aspect of the midbrain. T. S of midbrain at the level of inferior colliculus , showing the location of trochlear nucleus (at the base of periaquaductal grey matter) and course of trochlear N. Fs. ØIt runs in lateral wall of cavernus sinus and enter the orbit through sup. orbital fissure to supply S. O.

VI : Abducens Nerve : ØLike trochlear N. , contains only somatic motor neurones in the abducens nucleus , which located in caudal pons beneath the floor of 4 th ventricle. ØFibres emerge from the ventral surface of brain stem at the junction between the pons & pyramid of M. O ØThe nerve then passes in the cavernous sinus and enter orbit through sup. orbital fissure to supply L. R muscle to abduct the eyeball.

Lesions of cranial nerves III, IV and VI : ØOculomotor N. palsy by a lesion of occulomotor nucleus in mibrain or compression by aneurysm or tumour leads to ptosis , dilatation of pupil that is unresponsive to light & accommodation reflexes and inability to move eyeball upwards, downwards and inwards (adduction). ØAbducens N. palsy leads to inability to move the eyeball outwards (abduction). ØNote right ptosis. ØCombined unilateral palsies of III, ØNote with elevation of eyelid, the eyeball can be IV, and VI during their course in seen abducted and the pupil dilated. cavernous sinus , sup. Orbital fissure or ØNote failure of left eyeball abduction due to within the orbit , lead to: lesion of left abducent N. 1 -ptosis. 2 -dilatation of pupil. 3 -paralysis of all eye movements

V : Trigeminal Nerve : ØIt is the largest cranial N. , it has both sensory Fs. that are distributed via ophthalmic, maxillary and mandibular to the head --- & motor Fs. to Ms. of mastications (Ms. of 1 st arch). Superficial distribution of sensory fibres of the 3 divisions of trigeminal nerve. ØIt attaches to the ventrolateral aspect of pons by 2 roots (a large sensory laterally & a smaller motor medially).

V : Sensory components of Trigeminal Nerve : ØTrigeminal sensory nucleus Brain stem and location of trigeminal sensory nucleus & its major connections. consists of 3 -subnuclei : 1 -Chief (principle) sensory nucleus lies in pontine tegmentum (midpon), it recevies touch sensation. 2 -Spinal nucleus extends caudally through the medulla and upper cervical spinal cord to become continuous with substantia gelatinosa, it recevies pain & temp. sensation from face & scalp. 3 -Mesencephalic nucleus in midbrain, it recevies proprioception (deep) sensation from head.

Sensory components of Trigeminal nerve (for touch/pressure & pain/temperature) : ØAfferent Fs. of touch, pressure, pain & temperature are recevied from skin of face , scalp, via peripheral processes (ophthalmic, maxillary+sensory part of mandibular)… whose cell bodies (first neurones) are situated in trigeminal ganglion, located at the convergence of ophthalmic , maxillary and mandibular nerves. Brain stem and location of trigeminal sensory nucleus & its major connections. ØAfferent Fs. (centeral axons) conveying touch terminate in principal nucleus, and those carrying pain & temp. end in nucleus of spinal tract of trigeminal.

Sensory components of Trigeminal nerve (for proprioceptive sensation): st Ø 1 neurone for Proprioceptive : peripheral afferents (via mandibular nerve) from Ms. of mustication & temporomandibular joint have their cell bodies not in trigeminal ganglion but in mesencephalic nucleus of trigeminal ( the only primary afferents to have cell bodies within C. N. S). ØThe centeral axons of the cells of mesencephalic nucleus descend medially to synapse around Motor Nucleus of Trigeminal (2 ND neurone) in pons. Brain stem and location of trigeminal sensory nucleus & its major connections. ØAxons arising from 2 nd neurones in trigeminal nuclei (sensory &motor) decussate to form contralateral trigemino-thalamic tract, which terminates in contralateral (VP) nucleus of thalamus that sends Fs. to sensory cortex.

Motor components of Trigeminal Nerve : ØThe motor Fs. of trigeminal N. arise from the trigeminal motor nucleus , which lies in pontine tegmentum. T. S of pons at the level of Trigeminal nuclei. ØThe axons leave the pons to join the mandibular division of trigeminal , to innervate : 1 - 4 Ms. of mastication. 2 - 4 other Ms. : mylohyoid, anterior belly of digastric, tensor palati (soft palate) & tensor tympani (middle ear).

Lesions of Trigeminal Nerve : n n Herpes Zoster infection of sensory root of trigeminal N. …. . Leads to severe stabbing pain & eruption of vesicles localised to skin supplied by its branches : ophthalmic , or maxillary or mandibular N…. . Trigeminal Neuralgia. Syringo-bulbia , it is a disease of unknown etiology which affects the closed M. O, causes central cavitation of medulla caudal to 4 th V. , leading to destruction & damage of decussating trigemino-thalamic Fs. , causing selective loss of pain & temp. sensation in the face ( dissociated sensory loss), mostly leading to destruction of the cervical spinal cord (syringomyelia) =cavitation of spinal cord.

VII : Facial Nerve : ØIt carries 3 -types of fibres : 1 - Efferent motor (branchiomotor) Fs. From facial motor nucleus in pons to : Ms. of 2 nd arch , Ms. of facial expression & stapedius. 2 -Afferent Taste sensory Fs. From anterior 2/3 of tongue. These Fs. are processes of cells in sensory geniculate ganglion in middle ear , and run in nervus intermedius to end in nucleus solitarius in M. O. 3 -Efferent parasympathetic secretomotor Fs. Carried by lateral root of facial nerve (nervus intermedius) From sup. salivary nucleus in pons : to pterygopalatine & submandibular ganglia to lacrimal gland , palate, nasal & oral m. m, /and submandibular & sublingual salivary glands.

VII : Facial Nerve : ØThe lateral root contains sensory & parasymp. Fs. is called nervus intermedius , / but the medial root is the motor root. ØThe sensory Fs. ends in nucleus solitarius in medulla and then Fs. project to V. P. nucleus of thalamus, which sends Fs. to sensory cortex of parietal lobe.

VII : Facial Nerve : ØMotor Fs. of facial nucleus in pons , via facial N. looping over abducens nucleus , then leaving the brain stem to supply : Ms. of facial expression , platysma , stylohyoid , post. belly of digastric & stapedius of middle ear. ØFacial motor nucleus receives other afferents from area of brain stem for mediation of certain reflexes and also from cerebral cortex , (cortico-bulbar pyramidal tract).

VII : Facial Nerve : ØReflex connections mediate 1 - protective eye closure in response to sudden strong stimuli through tectobulbar Fs. descending from sup. Colliculus (tectum of midbrain) to end in facial motor nucleus, then, via facial N. to supply orbicularis oculi to close & protect the eye. 2 - corneal reflex through Fs. from trigeminal sensory nucleus, to motor nucleus of facial, then via facial N. to orbicularis oculi in response to tactile stimulation of cornea. ØAfferents from cortical motor areas (cotico-bulbar Fs. ) supply Ms. of upper face which are distributed bilaterally (from Rt. & left C. hemispheres) , but those supplying Ms. of lower face are crossed. So, Unilateral upper motor neurone

Bell’s Palsy : LMN facial paralysis n It is due to acute unilateral inflammation of facial Ø Ø nerve within the skull (in facial canal). Manifested by paralysis of facial muscles of upper & lower parts of face on the same side of lesion. . Manifested by pain around ear , - failure to close eye, absent corneal reflex, - loss of taste sensation in anterior 2/3 of tongue, & hyperacusis =increased sound perception due to paralysis of stapedius. (action of stapedius = damping down the intensity of high pitched sounds by damping down movement of stapes) Ø If herpes zoster virus is the inflammatory agent , a vesicular rash appear in ext. auditory canal & m. m of oropharynx (Ramsay Hunt syndrome).

VIII : Vestibulocochlear Nerve : ØIt is purely sensory nerve. ØIt has 2 -components , 1 - Vestibular N. , which carries balance sensation from utricle, sacule & semicercular canals. 2 - Cochlear N. , which carries hearing sensation. ØIt emerges from ponto-medullary junction at cerebello-pontine angle with the facial N.

VIII : Vestibular Nerve : ØCells of origin : vestibular ganglion , lying in internal acoustic meatus. ØThe peripheral process : carries sensation from utricle, saccule & semicircular canals (membranous labyrinth). ØCentral process : leaves vestibular ganglion and joins cochlear N. Distribution of Vestibular Nerve ØThey enter the brain in groove between pons & M. O. to end in the Vestibular nuclei in M. O.

Vestibular Nerve Fibres : 1 -Efferent Fs. From the 4 vestibular nuclei to cerebellum ( flocculo-nodular lobe) through inferior cerebellar peduncle to control body balance (equilibrium). 2 -Efferent Fs. descend uncrossed to spinal cord from lateral vestibular (Deiter’s)nucleus) to form vestibulospinal tract , assist to maintain balance by influencing muscle tone of body. 3 -Efferent Fs. Also pass to ocular nuclei of oculomotor , trochlear & abducent through medial longitudinal Vestibular nerve nuclei & their central fasciculus , for coordination of head & connections (rostral M. O. ) eye movements.

Vestibular Nerve Fibres : 4 -Efferent Fs. ascend from vestibular nuclei to relay in (VP) nucleus of thalamus to reach the cerebral cortex , at the vestibular area of sensory cortex which is uncertain but is probably adjacent to primary sensory cortex area in parietal lobe at inferior parietal lobule just above lateral fissure or adjacent to auditory cortex in temporal lobe. Vestibular nerve nuclei & their central connections

Lateral aspect of cerebral hemisphere location of vestibular area in cerebral cortex : probably adjacent to the sensory cortex in parietal lobe/ or adjacent to auditory cortex in temporal lobe.

Ø Cochlear Nerve : Ø 1 st order neurones conduct impulses of sound from the organ of Corti in the cochlea. ØFs. of cochlear N. are the central processes of nerve cells located in spiral ganglion. ØThe Fs. bifurcate to end in dorsal & venteral cochlear nuclei , which lie close to inf. cerebellar peduncle. Ascending connections of auditory component of vestibulo-cochlear nerve.

Ø 2 nd order neurones arise from cochlear nuclei into pons, some Fs. Cross to opposite side as trapezoid body. ØAt trapezoid body some Fs. may terminate in superior olivary nucleus. ØMost Fs. Ascend from sup. olivary nuclei to form the lateral lemniscus in pons, then ascend to end in inferior colliculus of midbrain. Ascending connections of auditory component of vestibulo-cochlear nerve. ØSome Fs. end in nucleus of lateral lemniscus in pons to establish reflex connections with motor trigeminal & facial nuclei, mediating cotraction of tensor tympani & stapedius Ms. In response to loud noise.

ØThe inferior colliculus sends axons to medial geniculate nucleus of thalamus. Ø 3 rd order neurone : axons arise from MGN pass through internal capsule to primary auditory cortex, which is located in Heschl’s gyri lying in superior temporal gyrus and hidden within the lateral fissure Ascending connections of auditory component of vestibulo-cochlear nerve. ØAuditory association cortex ( Wernick’s area) is an area of temporal lobe surrounding the primary auditory cortex , in which the auditory information is interpreted ( for knowing the

Lateral aspect of cerebral hemisphere Note primary auditory cortex & Wernicke’s area in superior temporal gyrus.

Acoustic Neuroma : It is a benign tumour of vestibulocochlear nerve leads to compression of the nerve & adjacent structures in cerebello-pontine angle. n So, there is attacks of dizziness & deafness. n With expansion of tumour, ataxia (disturbances of voluntary movement) & paralysis of cranial Ns. (especially V-VII) and the limbs follow due to damage of pyramidal Fs. n

IX : Glossopharyngeal Nerve : ØIt is a mixed N. , attached lateral to olive in rostral medulla and leaves the skull through jugular foramen. Glossopharyngeal nerve nuclei & their central connections ØIt receives afferent Fs. From : 1 -Receptors of general sensation in pharynx, post. 1/3 of tongue, eustachian tube & middle ear. 2 - Taste buds of pharynx & post. 1/3 of tongue. 3 - Chemoreceptors in carotid body & Baroreceptors in the carotid sinus.

IX : Glossopharyngeal Nerve Fibres : 1 -Afferent Fs. for general sensation : end in trigeminal sensory nucleus. -Fibres carrying touch sensation from back of tongue +pharynx are important for mediating gag reflex, through connection with nucleus ambiguus & hypoglossal nucleus. Glossopharyngeal nerve nuclei & their central connections. Red= motor, brown=parasymp. , blue=sensory 2 -Afferent visceral (chemo-& baroreceptors) & taste Fs. : end in nucleus solitarius of medulla.

IX : Glossopharyngeal Nerve Fibres : 3 -Efferent motor Fibres : arises from its motor nucleus in the rostral part of nucleus ambiguus of medulla to supply stylopharyngeus involved in swallowing. 4 -Efferent Parasympathetic Fibres : arises from inferior salivary nucleus of rostral medulla to synapse in otic ganglion, then via post-ganglionic Fs. innervate parotid gland. Glossopharyngeal nerve nuclei & their central connections. Red= motor, brown=parasymp. , blue=sensory

X : Vagus Nerve : Vagus nerve Nuclei & their central connections. ØIt is mixed nerve, attached lateral to olive of medulla caudal to glosso-pharyngeal N. in groove between olive & inf. cerebellar peduncle. ØIt recevies afferent Fs. from : 1 -Receptors for general sensation in pharynx, larynx, tympanic membrane, ext. acoustic meatus. 2 - Chemoreceptors in aortic bodies and baroreceptors in aortic arch. 3 -Receptors in thoracic & abdominal viscera.

X : Vagus Nerve Fibres : 1 -Afferent Fs. for general sensation : end in sensory nucleus of trigeminl and visceral sensory afferents end in nucleus solitarius. 2 -Efferent Motor Fs. : arise from nucleus ambiguus of medulla (main motor nucleus of vagus) to innervate Ms. of soft palate, pharynx, larynx to control swallowing and speech. 3 -Efferent Parasymp. Fs. : arise Vagus nerve Nuclei & their central from dorsal motor nucleus of connections. vagus to supply CVS, RS, &

XI : Accessory Nerve : ØIt is purely motor , consists of cranial part & spinal part. ØThe cranial part emerges from lateral aspect of medulla below vagus N. It arises from caudal part of nucleus ambiguus of medulla. At the level of jugular foramen it joins vagus. N. to supply Ms. of soft palate, pharynx & larynx. Diagram of caudal medulla & rostral spinal cord to illustrate origin and course of vagus & accessory nerves. ØSpinal root of accessory arises from upper 5 cervical spinal cord segments. It ascends to the side of medulla to join the cranial root till the jugular F. , it separates to supply sternomastoid & trapezius Ms.

XII : Hypoglossal Nerve : ØIt is purely motor , supplying all extrinsic & intrinsic Ms. of tongue except palatoglossus (by pharyngeal plexus). ØIt arises from hypoglossal nucleus in medulla ( beneath floor of 4 th V. ). ØIt emerges from M. O. between olive & pyramid. ØIt also receives coticobulbar Fs. from contralateral motor cortex, which T. S. of medulla to illustrate origin subserve voluntary movements of & course of hypoglossal nerve. tongue as occur in speech.

Motor neurone disease and lesions of cranial nerves IX-XII : n n n Occures in those over 50 years due to chronic degeneration of cortico-bulbar tracts projecting to nucleus ambiguus (sends motor Fs. in 9, 10, 11 nerves) & hypoglossal nucleus , leading to dysphonia (difficulty in phonation), dysphagia (difficulty in swallowing) , dysarthria ( difficulty in articulation) and weakness & spasticity of tongue (pseudobulbar palsy). There is also degeneration of nucleus ambiguus & hypoglossal nucleus themselves, leading to dysphonia, dysphagia, dysarthria and weakness, wasting & fasciculation of tongue (bulbar palsy). IX-XII nerves can be damaged by tumours in skull foramina, lead to dysphonia, weakness, wasting & fasciculation of tongue and depression of gag reflex + wasting of sternomastoid & trapezius Ms.