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 ŕ 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 ŕ 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 ŕ 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 (ŕ 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 ŕ 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 ŕ 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
ŕ 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
receives innervation from tractus solitarius (V): sucking,
swallowing reflexes
UMN: tongue moves away from denervation
LMN: tongue moves towards denervation