Chapter 14 A Synopsis of the Cranial Nerves

Chapter 14  A Synopsis of the Cranial Nerves

Chapter 14 A Synopsis of the Cranial Nerves of the Brainstem Michelle-Lee Jones February 18, 2009 OUTLINE Introductory Points Cell Columns & Nuclei Motor & Sensory Cranial Nerves of the Medulla Oblongata Cranial Nerves of the Pons-Medulla Junction Cranial Nerves of the Pons Cranial Nerves of the Midbrain

Introductory Points Regarding the brainstem: Transit point for all ascending & descending tracts connecting the spinal cord to the forebrain Associated with the exit/entry & nuclei of 10/12 cranial nerves Lesions often involve cranial nerves & have long tract signs great localizing signs

Motor Cell Columns and Nuclei Recap: basal plate derivatives CN motor nuclei oriented in discontinuous rostrocaudal cell columns Nuclei from the same column possess common developmental, structural and functional features 3 motor cell columns: General Somatic Efferent (GSE), General Visceral

Efferent (GVE) & Special Visceral Efferent (SVE) Motor Cell Columns and Nuclei GSE column features: 1. Most medial & anterior to the ventricular space Nuclei include hypoglossal (XII), abducens (VI), trochlear (IV) & oculomotor (III) Motor neurons innervate skeletal muscle from head mesoderm tongue (occipital) &

extraocular muscles (orbit) [ mesoderm NOT located in pharyngeal arches] Motor Cell Columns and Nuclei 2. GVE preganglionic parasympathetic column features: Lateral to GSE Forms cranial portion of craniosacral division of visceromotor system (parasympathetic) & preganglionic fibres travel on the CN Nuclei include dorsal motor vagal nucleus (X), inferior salivatory nucleus (IX), superior salivatory

nucleus (VIIintermediate), Edinger-Westphal nucleus (III) Preganglionic axons peripheral ganglion postganglionic fibres visceral structure Motor Cell Columns and Nuclei 3. SVE: Most lateral motor column in medulla & pontine tegmentum

Nuclei include nucleus ambiguus (efferents on IX & X), facial motor nucleus & trigeminal motor nucleus Muscles innervated originate from mesenchyme located within the pharyngeal arches Motor Cell Columns and Nuclei Pharyngeal Arch Associated muscle I II III

IV Mastication (V) Facial expression (VII) Stylopharyngeus (IX) Pharynx constrictors, intrinsic laryngeal muscles (including vocalis), palatine muscles (except TVP), skeletal muscle upper half of esophagus (X) GSE GVE SVE

Sensory Cell Columns & Nuclei Recap: alar plate derivatives CN sensory nuclei oriented in continuous cell column Lateral location for sensory columns 3 sensory cell columns: Solitary tract and nucleus Vestibular/cochlear nuclei Trigeminal sensory nuclei Sensory Cell Columns & Nuclei Solitary tract & nucleus (CN VII, IX & X)

1. Visceral afferent centre of brainstem (solitary tract receives all the 1visceral afferent central processes) Taste or Special Visceral Afferent (SVA) fibres Gustatory nucleus (rostral area of solitary nucleus) General Visceral Afferent (GVA) fibres Cardiorespiratory nucleus (caudal area of the solitary nucleus)

Solitary tract & nucleus (medulla) do not extend rostrally beyond the pons-medulla junction (most rostral CN = VII) Sensory Cell Columns & Nuclei Vestibular/cochlear nuclei 2. Just posterior to solitary tract & nucleus

Includes medial & spinal vestibular nuclei, anterior and posterior cochlear nuclei at pons-medulla junction, superior and lateral vestibular nuclei (caudal pons) Sensory input from VIII only Hearing (SSA, exteroceptive) & balance and equilibrium (SSA, proprioceptive) Sensory Cell Columns & Nuclei Trigeminal sensory nuclei 3.

From spinal cord-medulla junction to rostral midbrain 3 subdivisions Spinal trigeminal nucleus (pars caudalis, pars interpolaris & pars oralis) lateral medulla to caudal pons Principal sensory nucleus (mid-pontine level) Mesencephalic nucleus (lateral to periaqueductal grey)

Sensory Cell Columns & Nuclei Trigeminal sensory nuclei 3. Principal sensory nucleus & particularly the spinal trigeminal nucleus GSA reception centre of brainstem Receives all the general somatic afferent (pain & thermal) central processes

CN V, VII, IX & X Cranial Nerves of the Medulla Oblongata (CN XII, XI, X & IX) Hypoglossal Nerve (Motor) Nucleus - internal to the hypoglossal trigone Course: anterior medulla lateral aspects of medial lemniscus & pyramids pre-olivary fissure (rootlets) hypoglossal canal

intrinsic tongue muscles + hypo-, stylo- & genioglossus muscles Hypoglossal Canal: XII nerve, emissary vein, meningeal branch from ascending pharyngeal artery (dura posterior fossa) Hypoglossal nucleus + fibres: supplied by anterior spinal artery (ASA) Medial Medullary Syndrome (ASA)

Deviation of tongue to side of lesion (GG) Contralateral hemiparesis (CST) Contralateral loss of position sense, vibration & 2-point discrimination (ML) Root lesion tongue deviation to side of lesion Hypoglossal nucleus + fibres:

Internal capsule lesion tongue deviation to the contralateral side (injury to crossed corticobulbar fibres innervating XII nucleus) Contralateral hemiplegia Drooping of facial muscles contralateral lower quadrant Accessory Nerve (Motor):

SCM and trapezius muscles are innervated by motor neurons in the cervical spinal cord (NOT MEDULLA) Cranial part of XI misnomer (XI fibres temporarily join vague, then separate to exit skull) Course: Cervical SC axons exit SC laterally merge to form nerve foramen magnum briefly join caudal part of X in post. fossa jugular foramen

Accessory Nerve (Motor): Root lesions: trapezius & SCM paralysis (ipsilateral shoulder droop & difficulty turning head to contralateral side) C-spine lesion above deficits are eclipsed by hemiplegia (CST) Internal capsule lesion similar deficits as above (uncrossed corticobulbar fibres to XI nucleus injured)

Vagus Nerve (Motor & Sensory): Intermediate location (b/w midline & lateral medulla); exits post-olivary sulcus (exits cranial cavity via jugular foramen) 2 ganglia immediately external to the foramen: Superior Ganglion (GSA)

Inferior Ganglion (GVA, SVA) Vagus Nerve - Motor cells of the medulla: 1. Dorsal motor nucleus of the vagus (GVE-PNS preganglionic) terminal (intramural) ganglia viscera (trachea, bronchi, heart, GI tract just proximal to splenic flexure Effects: bronchiole constriction, HR, blood flow, peristalsis, gut secretions 2. Nucleus Ambiguus (SVE) 4th pharyngeal arch muscles (refer to previous table) Vagus Nerve Sensory (GSA, GVA & SVA)

1. GSA (pain & thermal): 2. Small area of ear, part of external auditory meatus & dura posterior fossa superior ganglion (central processes to spinal trigeminal tract, thence to spinal trigeminal nucleus) GVA & SVA: Heart, aortic arch, pharynx & larynx, lungs, gut to level of

splenic flexure (GVA) + taste buds on epiglottis & tongue base (SVA) inferior ganglion (central processes to solitary tract, thence to solitary nucleus - cardiorespiratory & gustatory portions GSA SVA SVE GVE GVA Vagus Nerve Sensory (GSA, GVA & SVA)

Root lesion (vagus): dyphagia & dysarthria, no apparent lasting visceromotor dysfunction, taste NA & external auditory meatus GSA loss not key Unilateral medulla injury nucleus ambiguus (Tumours, vascular lesions, syringobulbia) Deficits as noted above

Bilateral medulla lesions aphonia, aphagia, dyspnea, or inspiratory stridor Critical, especially if dorsal motor nucleus Thyroid surgery recurrent laryngeal n. injury dysarthria Glossopharyngeal Nerve (Motor & Sensory) Leaves medulla @ postolivary sulcus, just rostral to vagus, leaves skull via jugular foramen

As with vagus, 2 ganglia: inferior ganglion (GVA, SVA) & superior ganglion (GSA) Glossopharyngeal Nerve - Motor Inferior salivatory nucleus (GVE PNS): axons join with tympanic nerve, then lesser petrosal nerve otic ganglion parotid gland Nucleus ambiguus (SVE): innervation of

stylopharyngeus that muscle that helps with swallowing & efferent part of gag reflex Glossopharyngeal Nerve Sensory GSA: Pinna, external auditory canal superior ganglion GVA: Parotid gland, oropharynx & carotid body inferior ganglion

SVA: Taste from posterior 1/3 inferior ganglion Glossopharyngeal Nerve Lesions Rare, usually with X & XI roots @ jugular foramen Nerve lesion: taste posterior 1/3, loss of ipsi. gag reflex (s-m X) Glossopharyngeal neuralgia:

attacks of intense idiopathic pain in pharynx, caudal tongue, tonsil,? middle ear Precipitated by spontaneous or artificial stimulation posterior oral cavity, swallowing or talking SVA GSA GVE GVA SVE

Jugular Foramen & associated syndromes Right Jugular Foramen medial, middle & caudal parts Jugular Foramen & associated syndromes Vernet syndrome

@ or just internal to the foramen Loss of sensation post 1/3 tongue (IX); loss of sensation in larynx & pharynx, dysarthria & dysphagia (X); weakness of ipsil. SCM & trapezius (XI) Collet-Sicard syndrome Immediately external to the jugular foramen Damage to IX, X, & XI + ipsil tongue weakness (hypoglossal canal is near foramen) Villaret syndrome includes above + sympathetic fibres (SCG)

ipsil Horners Cranial Nerves of the Pons-Medulla Junction (CN VIII, VII & VI) Vestibulocochlear Nerve (Almost exclusively sensory) Most lateral, centrally related to cochlear & vestibular nuclei; 2 parts originate from specialized receptors within petrous temporal

bone combined root in brainstem Internal acoustic meatus (IAM) contains VIII, VII & labyrinthine artery Cochlear part: Cochlear Spiral ganglion (bipolar cells) IAM Cochlear nuclei (ant. & post.) brainstem relay nuclei MGN auditory cortex Vestibulocochlear Nerve (Almost exclusively sensory)

Note cholinergic cells near the olivary nuclei olivocochlear tract (efferent cochlear bundle) inner & outer hair cells (dampen responses) Vestibular part: Ampullae of semicircular canals, utricle & saccule vestibular ganglion (bipolar cells) IAM PMJ vestibular nuclei (sup, inf, lat, med) in medulla & caudal pons cerebellum + oculomotor nuclei, etc. Vestibulocochlear Nerve

VIII nerve lesions: hearing loss, tinnitus, vertigo, dizziness, ataxia Cochlea, spiral ganglion or cochlear fibres lesions: ipsilateral sensorineural hearing loss Lesions to brainstem or higher: ability to localise/interpret sound in space, no hearing loss per se Conductive hearing loss: conduction through middle ear (typically ossicles) Tinnitus pertains to auditory portion of VIII (peripheral

or central damage) Vestibulocochlear Nerve Injury to vestibular fibres: vertigo (subjective pt moves or objective environment moves), nystagmus n/v Nystagmus vestibular influence over brainstem oculomotor control disconnected Lesions of vestibular nuclei & central connections vertigo, ataxia,

nystagmus, n/v Causes of vestibular dysfunction are myriad: Meds, trauma, DM, cerebellar lesions, vestibular schwannoma etc. Menieres syndrome: hearing loss, sound distortion, vertigo, unsteadiness standing or walking endolymphatic pressure size of utricle, saccule & cochlear Cerebellopontine Angle Lesions TUMOR TYPE Vestibular schwannomas Meningiomas

Epidermoid tumours 85% 5-10% 5% Prevalence @ CPA Origin/ Description

Schwann cells of vestibular root Margins of internal acoustic meatus (anterior, superior) Clinical manifestations

Tinnitus, unsteady gait, progressive hearing loss, later ipsil. facial weakness, if > 3 cm, impinge on V sensory pain Significant erosion of internal acoustic meatus

Early facial weakness then hearing loss & trigeminal root associated pain Entrapped clusters of epidermis anywhere in CNS

Lined with epithelium & contain cellular debris, proteins & cholesterol Spillage of cyst contents recurrent aseptic meningitis In CPA, deficits related to V, VII & VIII Facial Nerve (Motor & Sensory) (Petrous temporal bone)

Sortie Intermediate nerve: GVE + SVA + GSA + few GVA Facial Nerve At geniculate ganglion (internal genu), greater petrosal nerve formed by GVE-preganglionic PNS nerves from VII joins deep petrosal nerve to form nerve of the pterygoid canal pterygopalatine ganglion Post-ganglionic parasympathetic fibres join V2 orbit lacrimal gland

Small SVE branch stapedius muscle Larger SVE branch (chorda tympani) middle ear joins V3 lingual branch preglanglionic PNS fibres to submandibular ganglion, collects SVA taste afferent fibres (ant 2/3 tongue) SVE muscles of facial expression, post. belly digastric & stylohyoid

Facial Nerve Sensory: SVA: anterior 2/3 tongue lingual V3 changeover to chorda tympani to join VII nerve geniculate ganglion GSA: fewer in number; external ear & external auditory canal central course on VII geniculate ganglion GVA: few; mucous membrane of palate & nasopharynx

geniculate ganglion enter brainstem in intermediate nerve Facial Nerve Ipsilateral face motor cortex provides bilateral innervation to facial motor neurons of the upper face But, the face motor cortex projects only contralaterally to facial motor neurons of the lower face

Supranuclear lesions (face motor cortex or internal capsule) drooping of corner of mouth contralateral to the lesion (CENTRAL SEVEN LESION) Facial Nerve Peripheral lesions of VII (infranuclear): Bells palsy:

Injury proximal to geniculate ganglion & origin of greater petrosal nerve with ipsilateral findings paralysis of upper & lower portions of face mucosal secretion in nasal & oral cavities tear fluid production & salivary gland output cutaneous sensation external ear & external auditory canal

taste sensation on anterior 2/3 tongue hyperacusis Facial Nerve Peripheral lesions of VII (infranuclear): Distal to the geniculate ganglion but proximal to the origin of the chorda tympani & stapedial nerve

Ipsilateral salivation & taste, hyperacusis, facial expression Intact tear fluid production & mucosal surfaces (nasal & oral cavities) are unaffected b/c greater petrosal nerve is intact Caveat: Lesions distal to or @ stylomastoid foramen ipsil. function of all facial muscles in the absence of parasympathetic or taste dysfunction Facial Nerve

Corneal reflex: Afferent limb travels via V1 (ophthalmic) trigeminal ganglion spinal trigeminal tract spinal trigeminal nucleus trigeminothalamic fibres facial motor nucleus thalamus Facial diplegia Myotonic muscular dystrophy Mobius syndrome (upper > lower facial weakness typically, extraocular palsies, skeletal

& extremity defects) Lyme disease, GBS, Botulism poisoning & Corynebacterium diphtheriae Mobius syndrome Verzijl, Harriette T.F.M., van der Zwaag, Bert, Cruysberg, Johannes R.M., Padberg, George W. Mobius syndrome redefined: A syndrome of rhombencephalic maldevelopment Neurology 2003 61: 327-333 Facial Nerve

Hemifacial spasms: Irregular painful facial muscle contractions May be precipitated by voluntary facial movements or follows Bells palsy Can be 2 to compression of facial nerve root (e.g abnormal AICA branches) Abducens Nerve - Motor

Abducens nucleus: Internal to the facial colliculus, in rhomboid fossa floor just lateral to median sulcus, above stria medullaris (IV ventricle) Contains motor neurons (GSE) & interneurons Abducens nerve exits @ pons-medulla junction (pre-olivary sulcus) cavernous sinus

in close association with ICA superior orbital fissure ipsil. lateral rectus (LR) Abducens Nerve - Motor Interneurons in VI nucleus contralateral MLF oculomotor nucleus (ipsi to MLF) medial rectus (MR) Abducens fibres injury e.g. medial pontine syndrome flaccid paralysis of ipsilateral lateral rectus muscle (introverted eye,

impaired ipsil. abduction) Abducens Nerve - Motor Abducens nucleus injury (motor- & interneurons) e.g. IV ventricle tumour invading facial colliculus paralysis ipsi LR + contra. MR on gaze toward side of lesion (LMN of LR + INO) Medial longitudinal fasciculus lesions internuclear ophthalmoplegia e.g. MS

Injury only to internuclear axons Ipsil abduction intact nystagmus but adduction of contralateral eye is impaired Preserved adduction with convergence (vs. III ) MLF - INO Abducens Nerve - Motor One and a Half syndrome: Seen with pontine lesion affecting abducens nucleus

& fibres + adjacent MLF No movement of ipsilateral eye horizontally, contralateral eye horizontal movements restricted to abduction nystagmus Cortical Influence: Frontal eye fields (FEF) bilateral projection to PPRF (horizontal gaze centre) + ipsil. superior colliculus (SC) SC contralateral PPRF; PPRF ipsil VI nucleus Cortical damage (e.g. CVA, trauma) to FEF involuntary conjugate deviation of eyes to the side of the lesion

One-and-a-half syndrome. This results from a pontine lesion (shaded area) involving the paramedian pontine reticular formation (lateral gaze center) and medial longitudinal fasciculus, and sometimes also the abducens (VI) nucleus, and affecting the neuronal pathways indicated by dotted lines. Attempted gaze away from the lesion (A) activates the uninvolved right lateral gaze center and abducens (VI) nucleus; the right lateral rectus muscle contracts and the right eye abducts normally. Involvement of the medial longitudinal fasciculus interrupts the pathway to the left oculomotor (III) nucleus, and the left eye fails to adduct. On attempted gaze toward the lesion (B), the left lateral gaze center cannot be activated, and the eyes do not move. There is a complete (bilateral) gaze palsy in one direction (toward the lesion) and one-half (unilateral) gaze palsy in the other direction (away from the lesion), accounting for the name of the syndrome. Clinical Neurology 6th ed. Greenberg et. al Cranial Nerves of the Pons (CN V, IV, III)

Trigeminal - Motor & Sensory Introduction: Largest CN, exits from lateral pons Large sensory root (portio major) & small motor root (portio minor)

Exits border between basilar pons & middle cerebral peduncle V1 V2 V3 Trigeminal - Motor & Sensory Brief review: Sensory nuclei (caudal rostral):

Spinal trigeminal nucleus (pars caudalis, interpolaris & oralis), principal sensory nucleus & mesencephalic nucleus GSA exteroception: Pain, thermal & nondiscriminative touch fibres from head trigeminal ganglion + geniculate ganglion + superior ganglia for CN IX & X (ext. ear) spinal trigeminal tract/nucleus GSA exteroception for discriminative touch as above but go to principal sensory nucleus Trigeminal - Motor & Sensory

GSA proprioceptive input from masticatory muscles, EOM & periodontal ligament receptors mesencephalic nucleus Sensory input to spinal trigeminal nucleus & to principal sensory nucleus anterior & posterior trigeminothalamic tracts thalamus somatosensory cortex Trigeminal - Motor & Sensory

Motor nucleus of V 1st pharyngeal arch (medial & lateral pterygoid, tensor tympani, tensor veli palatini, mylohyoid, & anterior belly digastric) The motor root of V exits in the foramen ovale along with V3. Jaw Jerk reflex: Masticatory muscle receptors V2

mesencephalic nucleus bilateral projections from afferent collaterals trigeminal motor nucleus Trigeminal - Motor & Sensory Corneal (previously discussed) Lesions of V nerve or central nuclei Sensory sx in nerve distribution & masticatory muscle paralysis

Sensory deficits include: Complete loss of pain, temperature, tactile sensation ipsilateral face & scalp Loss of above sensations in oral cavity ipsil. Loss of corneal reflex Trigeminal - Motor & Sensory Tic douloureux (Trigeminal neuralgia)

Severe paroxysmal attacks of lacinating pain restricted to 1 subdvisions of V Trigger zones lip, nose, cheek Precipitants e.g. shaving, make-up application, chewing, talking etc. Possible malnourishment!!!

Patients usually > 35 years Maxillary > Mandibular > Ophthalmic Associated with MS, degenerative changes in trigeminal ganglion, vascular abn (e.g. SCA) contradicting autopsy evidence Status trigeminus tic like contractions masticatory muscles Trigeminal - Motor & Sensory Motor deficits: V root lesion ipsil masticatory muscle

weakness, jaw deviation to weak side (unopposed contralateral pterygoid) Central lesions (tumour, AVM, mets, vascular obstruction) Lateral Medullary syndrome (Wallenberg syndrome) Cranial Nerves of the Midbrain (CN IV, III)

Trochlear Motor Only motor CN to cross midline prior to exit & has long intracranial course Course: Trochlear nucleus (post. to MLF) @ level of IC arch around PAG decussates in anterior medullary velum exits brainstem immediately caudal to the contra. IC GSE motor axons superior cistern ambient cistern dura cavernous sinus superior orbital

fissure superior oblique (inf-lat) Trochlear Motor Trochlear motor neurons innervate contralateral superior oblique MLF + trochlear nucleus lesion e.g. MS: Contralateral S.O. paralysis

Ipsil INO Cotical input: FEF rostral interstitial nucleus of the MLF & superior colliculus riMLF = vertical gaze centre riMLF larger projection to ipsil IV nucleus & smaller projection to contra nucleus FEF injury involuntary conjugate gaze deviation to side of lesion

Oculomotor Motor Situated within ventral PAG, posterior to MLF, in rostral half of midbrain GSE all EOM except SO & LR Ipsilateral innervation except for SR neurons (decussate within the nucleus)

Just posterior to III complex is EdingerWestphal nucleus (GVE PNS) ciliary ganglion Oculomotor Motor Course:

III nerve fibres travel ventrally through & around the red nucleus exit @ interpeduncular fossa cavernous sinus superior orbital fissure Superior & inferior divisions of III in the orbit few branches to ciliary ganglion Ciliary ganglion (PNS) short ciliary nerves sphincter pupillae & ciliary muscles Oculomotor Motor

Post ganglionic sympathetic fibres from SCG travel on ICA plexus ophthalmic artery optic canal ciliary ganglion directly, nasociliary branch (V2) or oculomotor on route to ciliary ganglion In ciliary ganglion: SNS fibres continue directly into short ciliary nerves to dilator pupillae muscle, and others travel further via III nerve superior tarsal muscle Oculomotor Motor

Sensory input from the orbit via frontal & nasociliary nerves V1 trigeminal ganglion The III nucleus does not receive direct cortical input via the corticobulbar system Cortical control of III neurons via riMLF and SC; SC also projects to the riMLF; riMLF send significant input to ipsi III, less on contralateral side Cortical damage to FEF involuntary

conjugate deviation towards the side of lesion Oculomotor Motor Lesions of III nucleus, oculomotor nerve in interpeduncular cistern or III in cavernous sinus: EOM paralysis except for SO & LR ( abducted & depressed) Diplopia Pupil dilation, non-reactive to light, defective accommodation & ptosis Note that because of peripheral location of PNS fibres, subtle initial signs with external compression may be ptosis or mildly diminished pupil reactivity

prior to EOM dysfunction DM: EOM dysfunction sine visceromotor changes Ischemia affects the larger internal GSE motor axons 1st

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