10. Cranial Nerves

 

UMN: bilateral (except XII and lower facial muscles of VII: contralateral only)

LMN: ipsilateral (except IV: contralateral)

all sensory cortical areas pass through thalamus (except I)

 

therefore, UMN lesions tend to have bilateral (stronger contralateral) effects; LMN tend to have unilateral (ipsilateral) effects

 

UMN’s: primarily Area 4 à enter corona radiate and genu of internal capsule (collectively: corticobulbar tract)

                        - III, IV, VI: Areas 4 and 8

 

Midbrain (III – at level of SC, IV – at level of IC)

                        Edinger-Westphal Nucleus (III PS)

                        Oculomotor Nucleus (III)

                        Trochlear Nucleus (IV)

Pons (V,VI (level of cavernous sinus),VII,VIII)

                        Trigeminal Motor Nucleus (V)

                        Abducens Nucleus (VI)

                        Facial Motor Nucleus (VII): course around VI nucleus)

                        Vestibular Nucleus (VIII)

                        Cochlear Nucleus (VIII)

Medulla (IX, X, XII)

                        Superior Salivatory Nucleus (VII)

                        Inferior Salivatory Nucleus (IX)

                        Nucleus Ambiguus (IX, X)

                        Dorsal Vagal Nucleus (X)

                        Nucleus Solitarius (X)

                        Hypoglassal nucleus (XII)

Spinal cord transition (XI – “ventral horn” of medulla/spinal cord transition)

                        Accessory Nucleus (XI)

 

UMN signs and symptoms for cranial nerves below lesion

LMN signs and symptoms at level of lesion

 

palsy=paresis

strabismus: inability to direct both eyes so that the image will fall on both foveeas

 

I. Olfactory Nerve

 

rhinencephalon (close association with limbic system)

undergo mitosis throughout life

pathways are entirely ipsilateral (only cranial nerve to bypass thalamus)

primary olfactory neurons pass through cribriform plate

ammonia stimulates V

uncinate fits (preceded by disagreeable odors and stereotypic movement of lips and tongue)

CSF can leak from nose à meningitis, encephalitis

 

II. Optic Nerve

III. Oculomotor Nerve

 

All nuclei are located in the midbrain ventral to aqueduct of Sylvius (tegmentum) at level of SC

down and out” deviation if damaged

clinically: focus on medial rectus, eyelid, and pupil

note above about UMN (bilateral, stronger contralateral) vs. LMN (complete ipsilateral effect) lesions

LMN passes close to posterior communicating artery (look for subarachnoid aneurysm)

Supplies:

a.         all extraocular muscles (except superior oblique IV, and lateral rectus VI)

b.         levator palpebrae superioris (unpaired nucleus)

c.         ciliary muscle (accommodation)

d.         parasympathetic component à iris

 

IV. Trochlear Nerve

 

supplies: superior oblique

nucleus: level of IC, next to aqueduct (circle around: contralateral LMN)

LMN lesions: difficulty moving eye down and laterally, vertical diplopia (tilt head to compensate)

 

V. Trigeminal Nerve

 

sensory ganglia are analogous to DRG

sensory nuclei are analogous to synapses in Rexed I,II (Lissauer/marginal zone/substantia gelatinosa)

spinal tract and nucleus of V are continuous with dorsolateral fasciculus of Lissauer/marginal zone and substantia gelatinosa

V1, V2: Sensory only

V3: Sensory and Motor (mastication, tensor tympani)

 

Sensory

                        Ganglia

- trigeminal ganglion (à ophthalmic and maxillary (V1 and V2) nerves, sensory component of mandibular nerve(V3))

- mesencephalic nucleus = only DRG in CNS (proprioceptive information)

Nuclei

- Chief (Pontine) sensory nucleus (receives information about touch)

- Spinal trigeminal tract of V and nucleus (pain and temperature of face and forehead)

Motor

                        Nucleus

                        - Motor nucleus of V (medial to chief sensory nucleus of V): supplies muscles of mastication and tensor tympani

 

VI. Abducens

 

supplies: lateral rectus

nucleus: pons (fibers of VII cross over) = facial colliculus, close to midline

false localizing sign: LMN has long, complicated course (fibers can be stretched without being damaged)

                        - therefore, look for other pons signs before localizing lesion to pons

lesions à medial strabismus, horizontal diplopia (no ptosis)

VI nerve palsy can signal a potentially life-threatening condition (space-occupying lesion in pons)

exits at pontomedullary junction and enters cavernous sinus (in close proximity to V1 and V2)

 

VII. Facial Nerve

 

UMN lesions: lower (contralateral half only) face affected

Bell’s Palsy affects: taste (anterior 2/3), stapedius muscle (sounds will be loud), impairment of secretion (submandibular, sublingual, lacrimal)

 

Sensory

                        Ganglia

                        - geniculate ganglion (taste: anterior 2/3 of tongue)

                        Nucleus

                        - nucleus of tractus solitarius à VPM (ventral posterior nucleus, medial division)

Motor

                        Nucleus

                        motor nucleus of VII (loops around abducens nucleus): supplies muscles of face, stapedius

Parasympathetic

                        Nucleus

                        superior salivatory nucleus (salivation in response to odors)

 

VIII. Vestibulocochlear Nerve

IX. Glossopharyngeal; X. Vagus

 

Sensory: taste (posterior 1/3 of tongue), pharynx and epiglottis, carotid sinus and body, viscera of thorax and abdomen

Motor: muscles of soft palate

Parasympathetic: Heart rate, abdominal viscera

IX is involved in the gag reflex

Coughing, Gagging, Vomiting

 

XI. Spinal Accessory Nerve

 

supplies: sternocleidomastoid and trapezius muscles

LMN lesions: unable to turn head away from lesion, inability to shrug shoulders

à Cortico-spinal tract

 

XII. Hypoglossal Nerve

 

supplies: all intrinsic muscles of tongue, 3 out of 4 extrinsic muscles

genioglossus experiences contralateral only UMN innervation

nerve emerges between pyramid and olive in medulla; passes with IX and X close to ICA (sensitive to aneurysms)

receives innervation from tractus solitarius (V): sucking, swallowing reflexes

UMN: tongue moves away from denervation

LMN: tongue moves towards denervation