cranial nerves[med com]

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CRANIAL NERVES


Things to know for every Cranial nerve: 1. Constituent nuclei (both motor + sensory) (+/-)2. Course (intra-cranial + extra-cranial course)3. Exit from the brain/brainstem4. Exit or entry foramen in the skull5. Area of distribution6. Function, dysfunction (S/S)


OLFACTORY NERVE:Olfactory receptors: Olfactory mucosa (above superior concha), Cells (olfactory receptor cells, supporting cells, basal cells),

1. Coarse peripheral process with short cilia projecting into mucus membrane, 2. Fine central process passing via cribriform plate

Course: 1. Cribriform plate of ethmoid bone, 2. Olfactory bulb 3. Olfactory tract, 4. Olfactory stria (medial + lateral) as it reaches anterior perforating substance:

a. medial striae decussate, b. lateral goes into olfactory cortex (prepiriform area + periamygdaloid cortex) – primary olfactory

area (42)5. No relay in thalamus

Function: smellDysfunction: anosmia/hyposmia/dysosmia

OPTIC NERVE + VISUAL REFLEXES:VISUAL PATHWAY:

1. Retina (receptors; rods & cones – bipolar neurons – ganglionic cells going all the way to the LGB), a. RVF is projected onto the nasal retina of R – eye and temporal retina of L – eye.b. Vice versa for the LVF.

2. Upper field of vision projects onto the lower retinal quadrants & vice versa for lower field of vision3. OD (3 – 4 mm to the nasal side of the center of the eye ball), 4. Optic nerve – schwaan cell myelination, passes via optic canal, enters cranial fossa, optic chiasma (nasal &

temporal fibers), optic tract, LGN, optic radiations, visual cortex (area 17).5. Optic canal contents; ON + OA.6. Crossing: nasal fibers (including nasal macular fibers) cross in the optic chiasma, left field of vision (LVF) is

projected onto the right visual cortex, optic radiations and optic tract and vice versa (RVF on left side).

http://www.facebook.com/MedCom.20117. Optic radiations : (retro lenticular part of IC)8. Visual cortex: Calcarine sulcus, PVC (17), SVC (18, 19), cuneus, lingula9. Macular sparing in PCA stroke: Peripheral retina is represented anteriorly while the macula lutea is

represented posteriorly (might be projecting on the lateral side a bit; supplied by MCA)Fate of optic tract fibers:

LGN (visual pathway) Pretectal nucleus (LR; direct + consensual) SC (visual body reflex: tectospinal & tectobulbar fibers)

LIGHT REFLEX: 1. OT fibers enter into pretectal nucleus, 2. EDW (of both sides), 3. Preganglionic fibers (via parasympathetic root of oculomotor nerve), 4. Ciliary ganglion, 5. Post-ganglionic fibers (short ciliary nerves),

a. Constrictor pupillary muscle (miosis; less light entery + all light is directed to the central thickest part of the lens with highest refractive power) and

b. Ciliary muscle (near accommodation; suspensory ligaments relax – lens thickens/more globular i.e. increased refractive index).

CORNEAL REFLEX: (5, 7)Internuncial neuron is in the MLF

ACCOMMODATION REFLEX: Visual pathway uptil area 17, FEF (frontal eye field), corticonuclear/frontonuclear fibers to:

1. Oculomotor (3 rd ) nucleus: medial rectus muscle, convergence (adduction). 2. EDW (3 rd ): same as above (see light reflex)

http://www.facebook.com/MedCom.2011VISUAL BODY REFLEX:OT fibers enter into SC:

1. Tecto-bulbar fibers (efferents to all EOM nuclei; 3, 4, 6)2. Tecto-spinal fibers (efferents to anterior horn cells of cervical spinal cord)

(Movement of head, neck and eyes towards a visual stimulus, reading, etc)

PUPILLARY SKIN REFLEX: AFFERENT LIMB: EFFERENT LIMB:

Pre-ganglionic: Post-ganglionic:Pain afferent fibers (LST) – connected with the intermediolateral horn cells of T1 & T2 spinal cord

Preganglionic sympathetic fibers to superior cervical sympathetic ganglion

Postganglionic fibers in the ICA plexus (through the carotid canal)Long ciliary nerve (a branch of posterior ethmoidal nerve)Dilator pupillae muscle (mydriasis)

EDW NUCLEUS (ACCESSORY PARASYMPATHETIC NUCLEUS): Location: just posterior to the main oculomotor nucleus (superior mid brain section)REVISION: Afferents:

1. Optic tract - pretectal nucleus – EDW (VR pathway)2. Fronto (cortico-) nuclear fibers from FEF (accommodation reflex)3. I/L descending hypothalamic fibers

Efferents: (see above)

ARGYLL ROBERTSON PUPIL:AR present + LR absent

Superior orbital fissure: Upper part: LF4Middle part: NC, 3, 6Lower part: none


MAIN OCULOMOTOR NUCLEUS:Location: at level of SC, in the peri-aqueductal greyAfferents:

1. Corticonuclear fibers2. SC (tectobulbar fibers); visual body reflex3. MLF (connecting 3, 4, 6 and vestibular nuclei; vestibule-ocular reflex VOR)

Course of 3 rd cranial nerve : pass through the RN, interpeduncular fossa of midbrain, cavernous sinus (lateral wall), SOF (superior & inferior divisions pass through the CTR), orbital cavity.Functions:

1. Somatic (superior division: LPS, SR and inferior division: MR, IR, IOQ, parasympathetic root to ciliary ganglion); dysfunction: lateral strabismus, ptosis.

2. Parasympathetic; entering via parasympathetic root of oculomotor nerve – ciliary ganglion – postganglionic fibers via short ciliary nerve (sphincter pupillary, ciliary muscle; miosis and near accommodation).

TROCHLEAR NUCLEUS:Location: at level of IC, in the peri-aqueductal greyAfferents:

1. Corticobulbar fibers2. MLF (VOR)3. SC (tectobulbar fibers); visual body reflex

Efferents: motor fibers to SOQ muscle; rotating the eye ball to look downwards & outwards 3 x actions: (abduction, depression, intorsion)Course of trochlear nerve: exits posterior to midbrain, decussates in superior medullary velum, cavernous sinus (lateral wall), SOF (above the CTR), orbital cavity, SOQ muscle.

ABDUCENT NUCLEUS:Afferents:

1. Corticonuclear fibers2. SC (tecto bulbar fibers); visual body reflex3. MLF (VOR)

Efferents:

http://www.facebook.com/MedCom.2011LR muscleFunction: lateral deviation of eye ball (abduction)Dysfunction: medial strabismus.Course of 6 th nerve: facial colliculus (facial motor nucleus fibers winding around the abducent nucleus), cavernous sinus (inferolateral to ICA), SOF (through the CTR), orbital cavity, LR muscle.

Postganglionic sympathetic fibers to ORBIT & eye ball:Intermediolateral horn of spinal cord T1 and/or T2Pre-ganglionic fibers to superior cervical sympathetic ganglionPostganglionic sympathetic fibers along ICA, carotid canalEnter orbit along ophthalmic artery3 routes:

a) Directly enter ciliary ganglion via sympathetic root through common tendinous ring – CG – short ciliary nerve

b) Travel in nasociliary nerve & distributed to CG via sensory root – CG – short ciliary nervec) Travel in nasociliary nerve & go straight via long ciliary nerve

Supplies dilator pupillae muscle and blood vessels (vasoconstriction).

Ciliary ganglion inputs/roots:Parasympathetic motor root : (Brings in parasympathetic preganglionic motor fibers from the inferior division of oculomotor nerve) – Post-ganglionic fibers (short ciliary nerve) – sphincter pupillae & ciliary muscle.Sympathetic root:(Brings in postganglionic sympathetic fibers – short ciliary nerve)Sensory root:(Carries sensory fibers + brings in postganglionic sympathetic fibers – short ciliary nerve).

Action diagram (function of extra-ocular muscles):


MOVEMENTS ON AXIS:

Elevators x 3: Depressors x 3: Intortors x 2: Extortors x 2: Adductors x 3: Abductors x 3:

TRIGEMINAL NUCLEAR COMPLEX:1. Mesencephalic sensory nucleus (proprioception; muscles of mastication, facial muscles, EOM)2. Main trigeminal sensory nucleus (posterior column sensations); from face, sinuses, meninges3. Spinal sensory nucleus (pain, temperature, etc); from face, sinuses, meninges – descends down up to C2

levelProximal course: Decussation, trigeminal leminiscus, VPM (thalamus), post central gyrus (cerebral cortex).

4. Trigeminal motor nucleusMesencephalic nucleus (jaw jerk reflex) – sensory limb – mesencephalic nucleus (a sensory nucleus) – trigeminal motor nucleus – motor limb to muscles of mastication.

Efferents: 1. Muscles of mastication (temporalis, masseter muscle, medial and lateral pterygoid muscles)2. Tensor tympani muscle – to the malleus (dysfunction: hyperacusis)3. Tensor veli palatini muscle (the ‘hamulus-pulley’ muscle of soft palate)4. Mylohyoid (nerve to mylohyoid, inferior alveolar nerve, posterior div of mandibular, trigeminal nerve)5. Anterior belly of digastric muscle (nerve to mylohyoid)

Ophthalmic nerve (mainly sensory):First division of trigeminal nerveCavernous sinus (lateral wall; inferior to 3rd & 4th cranial nerves)Divides into: LFN (lacrimal, frontal & nasociliary nerves); from lateral to medialEnters orbit via SOF (L and F – above common tendinous ring while NC goes through it)

Lacrimal nerve:Runs along the upper border of LR muscleSupplies lacrimal gland, conjunctiva & upper eye lid (upper & lateral parts)

http://www.facebook.com/MedCom.2011Receives a communication from ZT branch of maxillary nerve carrying secretomotor (postganglionic sympathetic & parasympathetic) fibers for the lacrimal gland.

Frontal nerve:SOF (above common tendinous ring)Moves b/w levator palpebrae superioris & LR muscles2 terminal branches: (supplying conjunctiva, upper eye lid and skin)

1. Supra-trochlear (receives sensory innervation from uptil forehead)2. Supra-orbital (receives sensory innervation from uptil vertex of scalp)

Nasociliary nerve:SOF (through common tendinous ring along with 3rd; superior + inferior branches & 6th cranial nerves)Most deeply placed nervePasses medially deep to SR muscleComes b/w SOQ & MR musclesBranches:

1. Sensory root to CG (sensory fibers + post ganglionic sympathetic fibers)2. Long ciliary nerve (postganglionic sympathetic fibers)3. Posterior ethmoidal nerve (posterior ethmoidal foramen, ethmoidal & sphenoidal sinus)4. Anterior ethmoidal nerve (anterior ethmoidal foramen, anterior cranial fossa, nasal cavity, skin of lower

half of nose)5. Infra-trochlear nerve (medial parts of upper + lower eye lids, lacrimal sac, skin of upper half of nose)

Maxillary nerve (mainly sensory):

ONPP = branches of pterygopalatine ganglion (orbital, nasal, palatine, pharyngeal)Remaining = branhces of maxillary nerve (nasal & nasopalatine, infra-orbital & superior alveolar branches, zygomatic nerve (ZT, ZF, communicating branch to lacrimal branch of ophthalmic div of trigeminal nerve)

Mandibular nerve (mainly motor):Meningeal branch (ascends into cranial cavity via foramen spinosum along with MMA)Nerve to medial pterygoid muscle (which gives off branches to tensor tympani & tensor veli palatini before supplying medial pterygoid muscle)

Anterior trunk Posterior trunkDeep temporal nerves (2 x branches),Nerve to lateral pterygoid,

Auriculotemporal (scalp),Lingual, chorda tympani (from the facial nerve)

http://www.facebook.com/MedCom.2011Nerve to masseter,Buccal nerve.

Inferior alveolar & its 2 terminal branches (mental + incisive nerves),Nerve to mylohyoid.lesser petrosal nerve (a branch of glossopharyngeal nerve-tympanic plexus)

FACIAL NERVE NUCLEI: (have studied in detail)

Parasympathetic nuclei (GVE):Superior salivatory nucleus: Efferents: submandibular, sublingual salivary glandsLacrimal nucleus: lacrimal gland

Lacrimal gland: SSN (facial nerve nucleus), nervus intermedius, geniculate ganglion (passes through it), great petrosal nerve, combines with deep petrosal nerve (brings sympathetics from ICA plexus), nerve of pterygoid canal, pterygopalatine ganglion (sphenopalatine ganglion), postganglionic neuron enters into maxillary nerve via 2 x ganglionic branches, zygomaticotemporal nerve branch of zygomatic nerve, enters into ophthalmic nerve, lacrimal branch (on superior surface of LR muscle), lacrimal gland. Submandibular & sublingual salivary glands:SSN (facial nerve nucleus), chorda tympani, enters into lingual nerve, submandibular ganglion, postganglionic neuron enters back into lingula nerve, submandibular & sublingual salivary glands.

Facial motor nucleus (Branchiomotor nucleus, SVE):Afferents:

1. Corticonuclear fibers (LMN and UMN + significance with respect to localization of level of lesion)Efferents:

1. Stapedius muscle (dysfunction: hearing loss)2. Posterior auricular muscle, occipital belly of occipito-frontalis3. Stylohyoid muscle, posterior belly of digastric muscle4. Facial muscles (voluntary facial muscle control)

Sensory nuclei: Nucleus of tractus solitarius; rostral: 7, 9, and 10Afferents: taste fibers from tongue (anterior part), lingual nerve, chorda tympani, facial nerve, geniculate ganglion, rostral part of nucleus of tractus solitariusEfferents: Taste fibers from nucleus of tractus solitaries go to the thalamus, IC, corona radiata, cortex (taste area) Trigeminal sensory nucleus: 5, 7, 9, 10General sensations go to trigeminal spinal sensory nucleus (Somatotopy – posterior part), VPM (thalamus), etc.

Course of facial nerve outside the brainstem: Motor root: it is formed by the facial motor nucleus, which forms the facial colliculus and then emerges out from the anterior surface of brainstem.Sensory root (nervus intermedius): it is formed by the central processes of the cells of geniculate ganglion + contains preganglionic efferent parasympathetic fibers for salivary glands as well (remember, trigeminal facial sensations go to the trigeminal spinal sensory nucleus).

The 2 x roots emerge from anterior surface of brainstem (b/w pons & MOB) – join together to form the facial nerve – enters into the petrous temporal bone vial internal acoustic meatus (along with Vestibulo-cochlear nerve + labyrinthine artery) – enters into facial canal (in the deeper part of IOM)


Geniculate ganglion:Gives off 3 branches:

a) Greater petrosal nerve (travels antero-medially through petrous temporal bone – comes out via hiatus of greater petrosal nerve – anterior surface of petrous bone – groove for greater petrosal nerve – carries preganglionic fibers from SSN – nerve of pterygoid canal – foramen lacerum – pterygoid canal - pterygopalatine ganglion in the pterygopalatine fossa).

b) Nerve to stapedius (stapedius muscle)c) Chorda tympani (comes out of facial nerve before it exits stylomastoid foramen – moves up – enters

middle ear cavity through its posterior wall – passes near the upper aspect of TM – enters the IT fossa via petrotympanic fissure – joins the lingual nerve in the IT fossa).

Comes out via stylomastoid foramen.

Facial nerve: (motor innervation after it comes out of the stylomastoid foramen)Posterior auricular nerve branch:

1. Occipital belly of occipito-frontalis muscle2. Posterior auricular muscle

Then supplies:3. Posterior belly of digastric4. Stylohyoid muscle

Inside the parotid it divides into:a) Temporofacial branch (facial muscles)b) Cervicofacial branch (facial muscles)

Five terminal branches for facial muscles:1. Temporal2. Zygomatic3. Buccal4. Mandibular5. Cervical

VESTIBULO-COCHLEAR NERVE NUCLEI:Vestibular nuclear complex (4 nuclei; inferior, medial, lateral, superior)Afferents:

Utricle + saccule - macula (linear acceleration), semicircular canals –crista ampullaris (angular acceleration), Vestibular nerve, Vestibular ganglion, Vestibular nuclei x 4

Efferents: Vestibulospinal tract (spinal cord); maintain balance and extensor muscle tone; to antigravity muscles. Vestibulocerebellar fibers: vermis and flocculonodular lobe Thalamus (VP nucleus), internal capsule, coronal radiate, cerebral cortex MLF (VOR)

Cochlear nuclei (2 nuclei; anterior/ventral and posterior/dorsal)Location: on sides of ICPAfferent:

Spiral organ of corti (basilar membrane in the cochlear duct), spiral ganglion, cochlear nuclei x 2Efferent:

Trapezoid body and trapezoid nucleus, SON (superior olivary nucleus), Lateral leminiscus and LL nuclei, Inferior colliculus, inferior brachium, MGB (thalamus), Internal capsule, coronal radiata, auditory cortex (areas 41 and 42).

Function: hearingDysfunction: U/L hearing loss (with damage uptil cochlear nuclei), tinnitus. Conductive & sensory neural hearing loss. Vertigo, balance problems, nausea & vomiting.


Note: 7th and 8th cranial nerves = cerebello-pontine angle9th, 10th and 11th cranial nerves = come out from behind olive12th cranial nerve = comes out from in b/w olive & pyramid

GLOSSOPHARYNGEAL NERVE NUCLEI:Course of nerve: comes out via the jugular foramen (alongwith 10th and 11the cranial nerves), carotid sheath (later comes out of it), winds around the stylopharyngeus muscle, enters into the oral cavity, passes in b/w ICA and ECA I think, then runs deep to the hyoglossus muscle in the oral cavity – you can see the detailed course from Book)

Motor nucleus (nucleus ambiguous); 9, 10, 11(only cranial part)Efferent: stylopharyngeus muscle (longitudinal muscle of the pharynx)

Parasympathetic nucleus (inferior salivatory nucleus):Efferent: tympanic branch of glossopharyngeal nerve, tympanic plexus, lesser petrosal nerve, otic ganglion, post-ganglionic fibers in the auriculotemporal nerve, parotid gland.

Sensory nuclei:Rostral nucleus of tractus solitarius (7, 9, 10): Afferent: Special taste sensations from posterior 1/3rd of tongue (pathway explained earlier via lingual and chorda tympani nerves and so on)Efferent:Anterior nucleus (thalamus), IC, corona radiate, cerebral cortex (taste area).

Caudal nucleus of tractus solitarius (9, 10):From baroreceptors at the bifurcation of CCA (common carotid artery)interneuronDorsal motor nucleus of vagus, vagus nerve, heart. Dysfunction: orthostatic hypotension

Trigeminal sensory nucleus (5, 7, 9, 10): general sensations:Afferents: general sensations (ear, tongue, pharynx, etc)

Glossopharyngeal shown on left and vagus shown on right below:


You should know the following reflexes:

1. Gag reflex: 2. Carotid sinus reflex:3. Aortic arch reflex:4. Brain-bridge right atrial reflex:

VAGUS NERVE NUCLEI:Course of nerve: jugular foramen, then course of individual branches, ……..Nucleus ambiguous: (9, 10, cranial 11)Efferents: larynx, pharynx muscles (pharyngeal branch, superior laryngeal nerve; internal & external laryngeal branches, recurrent laryngeal nerve; inferior laryngeal nerve) – courses of all from pharynx & larynx topics:

I am still not 100 % sure about the vago-accessory complex: ……….. ???Dysfunction: dysphagia, dysarthria, hoarseness of voice, nasal quality in voice, nasal regurgitation of fluid, absent gag reflex.Dorsal motor nucleus of Vagus (parasympathetic):Afferents:

Descending hypothalamics Afferents from carotid sinus (carotid sinus reflex) and baroreceptors (baroreceptor reflex).

Efferents: Involuntary muscles of bronchi, heart, esophagus, stomach, intestine (uptil distal 1/3rd of transverse colon)

Sensory nuclei: Rostral Nucleus of tractus solitarius: 7, 9, 10Afferents:

http://www.facebook.com/MedCom.2011Taste fibers from the posterior most part of tongue, inferior ganglion of vagus nerve, nucleus of tractus solitarius (rostral part)Efferents: Fibers decussate, VA nuclear group (thalamus), IC, corona radiate, cortex (taste area).

Caudal nucleus of tractus solitarius: 9, 10Carotid sinus (reflex)

Trigeminal nucleus: 5, 7, 9, 10Common sensations (ear, etc)Superior ganglion of vagus nerveTrigeminal leminiscus, VPM (thalamus), etcCourse of vagus nerve: jugular foramen, superior and inferior ganglia w.r.t. to the jugular foramen.Cranial root of accessory nerve joins below the inferior ganglion, later on separates once again and so on.

ACCESSORY NERVE:Cranial root:

1. Corticonuclear fibers2. Nucleus ambiguous3. Exit between olive and ICP 4. Joins spinal root5. Exit from jugular foramen6. Spinal root separates 7. Cranial root supplies structures with vagus nerve

Spinal root:1. Spinal nucleus (anterior gray column of spinal cord) C1 – C52. Spinal root course (passes underneath SCM, then runs in the floor of the posterior triangle of the neck,

then passes underneath the TPZ muscle)

http://www.facebook.com/MedCom.20113. Spinal root supplies: trapezius and sternocleidomastoid muscles (functions, dysfunctions).

HYPOGLOSSAL NERVE NUCLEUS:Course of nerve: comes out of hypoglossal canal, runs down, winds around the SCM branch of posterior auricular artery (I think so; double check plz). Crosses lateral to the ICA and ECA, runs in the floor of oral cavity lateral to hyoglossus muscle. Afferents: corticonuclear fibersEfferents: intrinsic muscles of tongueNerve emerges in b/w the pyramids and oliveDysfunction: tongue atrophy, weakness, tongue protrusion towards the opposite side.

Explanation: corticonuclear fibers to the genioglossus part of the hypoglossal nucleus are mostly crossed. Therefore:UMN lesion: causes tongue protrusion away from the lesion side, whileLMN lesion: causes tongue protrusion towards the side of the lesion.

cranial nerves[med com]

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