Chapter 14 – A Synopsis of the Cranial Nerves of the Brainstem

Chapter 14 – A Synopsis of the Cranial Nerves of the Brainstem

Michelle-Lee JonesFebruary 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)


1. GSE column features:• 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]


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 (VII–intermediate), Edinger-Westphal nucleus (III)

• Preganglionic axons peripheral ganglion postganglionic fibres visceral structure


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 NucleiPharyngeal

Arch Associated muscle

I Mastication (V)

II Facial expression (VII)

III Stylopharyngeus (IX)

IV 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 nucleusVestibular/cochlear nucleiTrigeminal sensory nuclei


1. Solitary tract & nucleus (CN VII, IX & X)• Visceral afferent centre of brainstem (solitary tract

receives all the 1°visceral 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)


2. Vestibular/cochlear nuclei• 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)

http://instruct.uwo.ca/anatomy/530/8nucl2.gif


3. Trigeminal sensory nuclei• 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)


3. Trigeminal sensory nuclei• 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):– 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)

2. 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

SVE

SVA

GSA

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

GSA

SVA

GVE

SVE

GVA

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 Horner’s

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. Meniere’s syndrome:

hearing loss, sound distortion, vertigo, unsteadiness standing or walking

endolymphatic pressure size of utricle, saccule & cochlear

Cerebellopontine Angle LesionsTUMOR TYPE

Vestibular schwannomas Meningiomas Epidermoid tumours

Prevalence @ CPA

85% 5-10% 5%

Origin/Description

Schwann cells of vestibular root

Margins of internal acoustic meatus (anterior, superior)

Entrapped clusters of epidermis anywhere in CNS

Lined with epithelium & contain cellular debris, proteins & cholesterol

Clinicalmanifestations

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

Spillage of cyst contents recurrent aseptic meningitis

In CPA, deficits related to V, VII & VIII

Facial Nerve (Motor & Sensory)

Intermediate nerve: GVE + SVA + GSA + few GVA

(Petrous temporal bone)

Sortie

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):

Bell’s 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 maldevelopmentNeurology 2003 61: 327-333

Facial Nerve

Hemifacial spasms: Irregular painful facial muscle

contractions May be precipitated by voluntary facial

movements or follows Bell’s 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

Clinical Neurology – 6th ed. Greenberg et. al

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.

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 & non-discriminative 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 Edinger-Westphal 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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Chapter 14 – A Synopsis of the Cranial Nerves of the Brainstem