Cranial nerves & Cranial Cranial nerves & Cranial nerve nuclei :nerve nuclei :

The base of the brain showing locations of cranial nerves

There are 12, paired cranial nerves.

The first 2 cranial Ns. attach directly to forebrain (frontal lobe) , while the rest attach to brain stem.

Olfactory system is attached to forebrain and is referred to as the limbic system, / optic N. also is discribed in visual pathway.

Cranial 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 Superficial attachements of Cranial nerves :Cranial nerves :

The base of the brain showing locations of cranial nerves

Occulomotor & trochlear Ns. are attached to midbrain.

Trigeminal N. is attached to antero-lateral surface of pons.

Abducent, Facial & vestibulo-cochlear Ns. are lying between pons & M.O. from medial to lateral.

Hypoglossal N. is attached to antero-lateral sulcus of M.O. / but glossopharyngeal, vagus & accessory Ns. are attached to postero-lateral sulcus of 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.

Afferent Nerve Nuclei :

Fibres 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.

Fibres carrying hearing & motion/ positional sense via vestibulo-cochlear N. terminate in cochlear & vestibular nuclei that are located in upper M.O.

Visceral afferents carrying taste sensation via facial & glossopharyngeal Ns., terminate in nucleus solitarius located in upper M.O.

Efferent Nerve Nuclei : Somatic efferent column :

supplies striated Ms. in head, including : yellow colour 1- Oculomotor nucleus.2-Trochlear nucleus. 3-Abducent nucleus. 4-Hypoglssal nucleus.

Branchiomotor (special visceral) efferent column : supplies striated Ms. derived from branchial arches, including : orange 1- Trigeminal motor nucleus. 2- Facial motor nucleus. 3- Nucleus ambiguus.

Parasympathetic (general visceral) efferent column : supplies glands & smooth Ms. of viscera , including : pink colour 1- Edinger- Westphal nucleus. 2- Sup.& Inf. Salivary nuclei. 3- Dorsal nucleus of vagus.

Somatic efferent Nerve Nuclei Oculomotor 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

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 Oculomotor & trochlear NervesNerves

Anterior view of midbrain

Oculomotor nerve : emerges from the medial aspect of each cerebral peduncle e.g. through the interpeduncular fossa.

Trochlear 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.

Posterior view of midbrain

Somatic efferent Nerve Nuclei : Abducent nucleus : lies

in the caudal pons , beneath floor of 4th vent. Its efferent Fs. run in abducent N. to supply L.R.

Hypoglossal 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

Trigeminal 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 1st pharyngeal arch as Ms. of mustication, mylohyoid, ant.belly of digastric, tensor tympani (middle ear) & tensor veli palatini.(soft palate).

Facial 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 2nd pharygeal arch (stylohyoid,post.belly of digastric).

Nucleus ambiguus : it is a long nucleus lies in M.O., sending motor Fs. in 9th ,10th & cranial root of 11th nerves to innervate Ms. of pharynx & larynx derived from 3,4& 6 pharyngeal arches.

Parasympathetic efferent Nerve Nuclei :Edinger-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.

Superior salivary nucleus : lies in pontine tegmentum, it gives preganglionic Fs. Via facial N. into pterygo-palatine & 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 :Inferior salivary

nucleus : lies in pontine tegmentum, sends pre-ganglionic Fs. Via glosso-pharyngeal N. into otic ganglion , which sends post-ganglionic Fs. to parotid gland.

Dorsal 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 : Cranial Nerves : III : III : Oculomotor N.Oculomotor N.

This 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.

This N. lying in the lateral wall of cavernus sinus before passes to orbit through sup.orbital fissure.

Eye movements brought Eye movements brought about by the extraocular about by the extraocular muscles :muscles :

Oculomotor nerve supplies sup.rectus, inf.rectus , medial rectus , inferior oblique & levator palpebrae superioris, so it elevates ,depresses and adducts the eyeball.

Trochlear N. supplies S.O, it depresses eyeball down & medial

Abducent N. supplies L.R , it abdducts eyeball.

T.S of T.S of midbrainmidbrain at the level of at the level of sup.colliculussup.colliculus to illustrate the to illustrate the pathway of pathway of pupillary light reflex.pupillary light reflex.If 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.

The constriction of the pupil of the non-illuminated eye is called consensual (indirect) light reflex.During the visual pathway ,small Fs. leave the optic tract to synape in the pretectal nucleus, which projects bilaterally Fs. to Edinger-Westphal nuclei of occulomotor ,that send efferent parasympathetic Fs. Via oculomotor nerves on both sides to sphincter pupillae ms.

Note that pretectal area involves in mediation of pupillary light reflex.

Accomodation Reflex :Accomodation Reflex :Fixation upon a nearby object, involves contraction of ciliary muscles to increase the convexity of lens, thus focusing the image.

It is also accompanied by pupillary constriction due to activation of constrictor pupillae m.

Also, 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 :IV : Trochlear Nerve :

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.

This 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.

Trchlear N. ,the only nerve emerges from the post.surface of brain - stem ,then appears on the ventral aspect of the midbrain.

It runs in lateral wall of cavernus sinus and enter the orbit through sup. orbital fissure to supply S.O.

VI : Abducens Nerve :VI : Abducens Nerve : Like trochlear N., contains only somatic motor neurones in the abducens nucleus ,which located in caudal pons beneath the floor of 4th ventricle.

Fibres emerge from the ventral surface of brain stem at the junction between the pons & pyramid of M.O

The 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 Lesions of cranial nerves III,IV and VI :and VI : Oculomotor 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).

Abducens N. palsy leads to inability to move the eyeball outwards (abduction).

Combined unilateral palsies of III, IV,and VI during their course in cavernous sinus , sup. Orbital fissure or within the orbit , lead to: 1-ptosis. 2-dilatation of pupil. 3-paralysis of all eye movements

Note right ptosis .

Note with elevation of eyelid, the eyeball can be seen abducted and the pupil dilated.

Note failure of left eyeball abduction due to lesion of left abducent N.

V : Trigeminal Nerve V : Trigeminal Nerve ::

Superficial distribution of sensory fibres of the 3 divisions of trigeminal nerve.

It 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 1st arch).

It attaches to the ventrolateral aspect of pons by 2 roots (a large sensory laterally & a smaller motor medially).

V : Sensory components V : Sensory components of Trigeminal Nerve : of Trigeminal Nerve :

Brain stem and location of trigeminal sensory nucleus & its major connections.

Trigeminal sensory nucleus consists of 3-subnuclei : 1-Chief (principle) sensory nucleus lies in pontine tegmentum (mid-pon), 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 Sensory components of Trigeminal nerve (for touch/pressure nerve (for touch/pressure & pain/temperature) :& pain/temperature) :

Brain stem and location of trigeminal sensory nucleus & its major connections.

Afferent 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.

Afferent 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 Sensory components of Trigeminal nerve (for nerve (for proprioceptive sensation)proprioceptive sensation)::

Brain stem and location of trigeminal sensory nucleus & its major connections.

1st neurone for Proprioceptive : peripheral afferents (via mandibular nerve) from Ms.of mustication & temporo-mandibular 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).

The centeral axons of the cells of mesencephalic nucleus descend medially to synapse around Motor Nucleus of Trigeminal (2ND neurone) in pons.

Axons arising from 2nd 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 :The motor Fs.of trigeminal N. arise from the trigeminal motor nucleus , which lies in pontine tegmentum.

The 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).

T.S of pons at the level of Trigeminal nuclei.

Lesions of Trigeminal Lesions of Trigeminal Nerve :Nerve :

Herpes Zoster infectionHerpes Zoster infection of of sensory root ofsensory root of trigeminal N.trigeminal N. ….. Leads to severe ….. Leads to severe stabbing painstabbing pain & & eruption of vesicleseruption of vesicles localised to skin supplied by localised to skin supplied by its branches : ophthalmic , or maxillary or its branches : ophthalmic , or maxillary or mandibular N….. mandibular N….. Trigeminal Neuralgia.Trigeminal Neuralgia.

Syringo-bulbiaSyringo-bulbia ,it is a disease of unknown ,it is a disease of unknown etiology which affects the etiology which affects the closed M.O,closed M.O, causes causes central cavitation of medulla caudal to 4central cavitation of medulla caudal to 4thth V. V. , , leading to leading to destruction &destruction & damage of decussating damage of decussating trigemino-thalamic Fs.,trigemino-thalamic Fs., causing causing selective loss of selective loss of pain & temp. sensation in the facepain & temp. sensation in the face ( dissociated sensory loss)( dissociated sensory loss), mostly , mostly leading to leading to destruction of the cervical spinal cord destruction of the cervical spinal cord (syringomyelia) =cavitation of spinal cord.(syringomyelia) =cavitation of spinal cord.

VII : Facial Nerve :VII : Facial Nerve :

This nerve carries 3-types of fibres : 1- Efferent motor (branchiomotor) Fs. From facial motor nucleus in pons to : Ms. of 2nd arch , Ms.of facial expression & stapedius. 2-Afferent Taste sensory Fs. From anterior 2/3 of tounge. These Fs. are processes of cells in sensory geniculate ganglion in middle ear , and run in nervus intermedius and end in nucleus solitarius, lying in M.O. 3-Efferent preganglionic parasympathetic secretomotor Fs. Carried by sensory 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 :VII : Facial Nerve :

The lateral root contains sensory & parasymp.Fs. is called nervus intermedius , but the medial root is the motor root.

The 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 :VII : Facial Nerve :

Motor Fs. of facial nucleus in pons , 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.

Facial 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 :VII : Facial Nerve :

Reflex connections mediate 1- protective eye closure in response to sudden strong visual stimuli through Fs. from sup. Colliculus (tectum of midbrain), 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. in response to tactile stimulation of cornea.

Afferents from cortical motor areas (cotico-bulbar Fs.) supply Ms. of upper face (frontalis & orbicularis oculi) are distributed bilaterally , but those supplying Ms. of lower face are crossed. So, Unilateral upper motor neurone lesion (UMNL) leads to lower facial Ms. paralysis of opposite side only, but upper Ms. are intact.

Bell’s Palsy :LMN facial Bell’s Palsy :LMN facial paralysis paralysis It is due to It is due to acute unilateral inflammationacute unilateral inflammation of of

facial nerve within the skull (in facial canal).facial nerve within the skull (in facial canal). Manifested by Manifested by paralysis of facial muscles of paralysis of facial muscles of

upper & lower parts of face (unilaterally)upper & lower parts of face (unilaterally) on the on the same side of lesion..same side of lesion.. pain around earpain around ear , - , - failure to close eye,failure to close eye, absent corneal reflex,absent corneal reflex, - - loss of taste sensation in anterior 2/3 of tongue, loss of taste sensation in anterior 2/3 of tongue, & & hyperacusis hyperacusis =increased sound perception =increased sound perception due to due to paralysis of stapedius.paralysis of stapedius.

If If herpes zoster virus herpes zoster virus is the inflammatory is the inflammatory agent , a agent , a vesicular rashvesicular rash appear in ext.auditory appear in ext.auditory canal & m.m of oropharynx canal & m.m of oropharynx (Ramsay Hunt (Ramsay Hunt syndrome).syndrome).

VIII : Vestibulocochlear VIII : Vestibulocochlear Nerve :Nerve :

It is purely sensory nerve.

It has 2-components , 1- Vestibular N., which carries sensation of position & movement of head (equilibrium), from utricle,sacule & semicercular canals. 2- Cochlear N., which carries hearing sensation.

It emerges from lower border of pons at ponto-medullary junction at cerebello-pontine angle with the facial N.

VIII : Vestibular VIII : Vestibular Nerve :Nerve :

Distribution of Vestibular Nerve

Cells of origin : vestibular ganglion ,lying in internal acoustic meatus.

The peripheral process : carries sensation from utricle,saccule & semicircular canals (membranous labyrinth).

Central process : leaves vestibular ganglion and joins cochlear N.

They enter the brain in groove between pons & M.O. to end in the Vestibular nuclei in M.O.

Vestibular Nerve Fibres :Vestibular Nerve Fibres :

Vestibular nerve nuclei & their central connections (rostral M.O.)

1-Efferent Fs. From the 4 vestibular nuclei pass to cerebellum ( flocculo-nodular lobe) through inferior cerebellar peduncle to control the body posture, & balance (equilibrium).

2-Efferent Fs. descend uncrossed to spinal cord from lateral vestibular (Deiter’s)nucleus and form vestibulo-spinal tract , assist to maintain balance by influencing muscle tone of limbs & trunk.

3-Efferent Fs. Also pass to ocular nuclei of oculomotor , trochlear & abducent nerves through medial longitudinal fasciculus , for coordination of head & eye movements.

Vestibular Nerve Fibres Vestibular Nerve Fibres ::

Vestibular nerve nuclei & their central connections

Efferent Fs. ascend from vestibular nuclei to relay in (VP) nuclei of thalamus to reach the cerebral cortex , at the vestibular area of sensory cortex which is uncertain but is probably adjacent to sensory cortex area in parietal lobe at inferior parietal lobule just above lateral fissure or adjacent to auditory cortex in temporal lobe.

Lateral aspect of cerebral Lateral aspect of cerebral hemispherehemisphere

location of vestibular area : probably adjacent to ‘head’ area of sensory cortex in parietal lobe/ or adjacent to auditory cortex in temporal lobe.

Ascending connections of auditory component of vestibulo-cochlear nerve.

Cochlear Nerve : 1st order neurones conduct impulses of sound from the organ of Corti in the cochlea.

These Fs. of cochlear N. are the processes of nerve cells located in spiral ganglion of cochlea.

The Fs.bifurcate to end in dorsal & venteral cochlear nuclei , which lie close to inf.cerebellar peduncle.

2nd order neurones arise from cochlear nuclei to ascend into pons, some Fs. Cross to opposite side as trapezoid body.

Ascending connections of auditory component of vestibulo-cochlear nerve.

At trapezoid body some Fs.may terminate in superior olivary nucleus , which gives rise olivo-cochlear Fs. Other Fs. Ascend from sup.olivary nuclei to form the lateral lemniscus in pons, then ascend to end in inferior colliculus of midbrain.

Some 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.

Ascending connections of auditory component of vestibulo-cochlear nerve.

The inferior colliculus sends axons to medial geniculate nucleus of thalamus.

3rd 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

Auditory association cortex ( Wernick’s area) is an area of temporal lobe surrounding the primary auditory cortex , in which the auditory information is interpreted.

Lateral aspect of cerebral Lateral aspect of cerebral hemispherehemisphere

Note primary auditory cortex & Wernicke’s area in superior temporal gyrus.

Acoustic Neuroma :Acoustic Neuroma : It is a benign tumour of It is a benign tumour of

vestibulocochlear nervevestibulocochlear nerve leads to leads to compression of the nerve & adjacent compression of the nerve & adjacent structures structures in in cerebello-pontine angle.cerebello-pontine angle.

So, there is So, there is attacks of dizziness & attacks of dizziness & deafness.deafness.

With expansion of tumour, With expansion of tumour, ataxia ataxia (disturbances of voluntary movement) (disturbances of voluntary movement) & & paralysis of cranialparalysis of cranial Ns.(especially V-VII)Ns.(especially V-VII) and and the limbs followthe limbs follow due to damage of pyramidal due to damage of pyramidal Fs.Fs.

IX : Glossopharyngeal IX : Glossopharyngeal Nerve :Nerve :

Glossopharyngeal nerve nuclei & their central connections

It is a mixed N. ,attached lateral to olive in rostral medulla and leaves the skull through jugular foramen.

It 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 IX : Glossopharyngeal Nerve Fibres :Fibres :

Glossopharyngeal nerve nuclei & their central connections. Red= motor, brown=parasymp.,blue=sensory

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 connections with nucleus ambiguus & hypoglossal nucleus.

2-Afferent visceral (chemo-& baroreceptors) & taste Fs. : end in nucleus solitarius of medulla.

IX : Glossopharyngeal Nerve IX : Glossopharyngeal Nerve Fibres :Fibres :

Glossopharyngeal nerve nuclei & their central connections. Red= motor, brown=parasymp.,blue=sensory

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 preganglionic Parasympathetic Fibres : arises from inferior salivary nucleus of rostral medulla to synapse in otic ganglion, then via postganglionic Fs.innervate parotid gland.

X : Vagus Nerve :X : Vagus Nerve :

Vagus nerve Nuclei & their central connections.

It is mixed nerve, attached lateral to olive of medulla caudal to glosso-pharyngeal N. in groove between olive & inf.cerebellar peduncle.

It 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 :X : Vagus Nerve Fibres :

Vagus nerve Nuclei & their central connections.

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 from dorsal nucleus of vagus to supply CVS,RS,& GITS.

XI :Accessory Nerve :XI :Accessory Nerve :

Diagram of caudal medulla & rostral spinal cord to illustrate origin and course of vagus & accessory nerves.

It is purely motor , consists of cranial part & spinal part.

The 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 vagusN. to supply Ms. of soft palate, pharynx & larynx.

Spinal root of accessory arises from anterior gray of upper 5 cervical 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 :XII : Hypoglossal Nerve :

T.S.of medulla to illustrate origin & course of hypoglossal nerve.

It is purely motor , supplying all extrinsic & intrinsic Ms. of tongue except palatoglossus (by pharyngeal plexus).

It arises from hypoglossal nucleus in medulla ( beneath floor of 4th V.).

It emerges from M.O. between olive & pyramid.

It also receives coticobulbar Fs. from contralateral motor cortex to supply Ms. of tongue for speech.

Motor neurone disease and Motor neurone disease and lesions of cranial nerves IX-lesions of cranial nerves IX-XII :XII :

Occures in those over 50 years due to Occures in those over 50 years due to chronic chronic degenerationdegeneration of cortico-bulbar tractsof cortico-bulbar tracts projecting projecting to to nucleus ambiguusnucleus ambiguus (sends motor Fs.in 9,10,11 (sends motor Fs.in 9,10,11 nervesnerves) &) & hypoglossal nucleus ,hypoglossal nucleus , leading to leading to dysphoniadysphonia (difficulty in phonation), (difficulty in phonation), dysphagia dysphagia (difficulty in swallowing) , (difficulty in swallowing) , dysarthria dysarthria ( difficulty in ( difficulty in articulation) and weakness & articulation) and weakness & spasticityspasticity of tongue of tongue (pseudobulbar palsy).(pseudobulbar palsy).

There is also degeneration of There is also degeneration of nucleus ambiguusnucleus ambiguus & & hypoglossalhypoglossal nucleus themselvesnucleus themselves, leading to , leading to dysphonia,dysphagia, dysarthria and weakness, dysphonia,dysphagia, dysarthria and weakness, wasting & wasting & fasciculationfasciculation of tongue of tongue (bulbar(bulbar palsy).palsy).

IX-XII nervesIX-XII nerves can be damagedcan be damaged by tumours by tumours in in skull foramina,skull foramina, lead to dysphonia, weakness, lead to dysphonia, weakness, wasting & fasciculation of tongue and depression of wasting & fasciculation of tongue and depression of gag reflexgag reflex with with unilateral wasting of sternomastoid unilateral wasting of sternomastoid & trapezius Ms. & trapezius Ms.