Lec 10 Cranial Nerves Flashcards
What does somatic efferent innervate?
skeletal muscles
What does visceral efferent innfervate?
scmooth muscle, cardiac muscle, or glands
Which CN is not considered part of the peripheral nervous system?
CN II [optic]
What are 2 exceptions to the rule that cortical innervation of CNs is bilateral?
parts of
- CN VII [facial]
- CN XII [hypoglossal]
What is significant about CN cortical innervation being bilateral?
- a unilateral cortical lesion would not significantly impact cranial nerve function
What is the 2, 4, 3 rule for Cn exit? Which cranial nerves are ignored in this rule?
- 2 out of midbrain: CN III, CN IV
- 4 out of pons: CN V, CN VI, CN VII, CN VIII
- 3 out of medulla: CN IX, CN X, CN XII
- ignores I, II, XI
Do the cranial nerves ever cross?
No, except the 4th CN
Are clinical findings on the same side or opposite side from cranial nerve involved?
same side!
How do you test for olfactory nerve clinically?
- close eyes, test each side individually with other nostril occluded
- place aromatic stimulus under nostril – coffee, chocolate
What is anosmia?
- loss of smell, often accompanies by loss of sensation of taste
- can be due to anterior cranial fossa fracture
What is parosmia? cause?
perversion of sense of smell
- due to temporal lobe pathology
What is CSF rhinorrhea? cause?
- can occur with cribiform plate fracture [trauma/tumor]
- get CSF leaking through dural tear
What is olfactory hallucination? cause?
- hallucinations of sense of smell [smell something that isn’t there]
- common with temporal lobe seizures
What is papilledema? significance?
- swelling of optic nerve
- usually sign of increased intracranial pressure
What is optic atrophy?
- pale optic nerve
what is optic neuritis? presentation?
- inflammatory response along optic nerve
- presents with pain on eye movement, central visual loss, decreased visual acuity, altered color vision
Where is primary visual cortex?
posterior pole of occipital
How can pituitary tumor affect optic?
- can compress optic chiasm and lead to visual field defects
What are the 4 parts to the CN2 examination?
- acuity [snellens]
- visual fields
- pupillary reflexes
- fundoscopy
What eye movements is medial rectus responsible for?
adduction
What eye movements is inferior rectus responsible for?
depression
What eye movements is superior rectus responsible for?
elevation
What eye movements is inferior oblique responsible for?
extorsion [rotate out]
What eye movements is superior oblique responsible for?
intorsion [rotate in]
CN IV
What eye movements is lateral rectus responsible for?
abduction
CN VI
Where do the fibers of occulomotor nerve arise?
from nucleus in midbrain at level of superior colliculus
What is function of edinger-westphal nucleus?
responsible for autonomic function of oculomotor –> pupillary constriction, lens accomodation
Where does the occulomotor nerve exit?
ventrally from interpeduncular foss of midbrain
Where does the occulomotor nerve enter the orbit?
through superior orbital fissure
What are signs of 3rd nerve palsy? Cause?
- wrinkled forehead, raised eyebrow, ptosis [drooped eyelid], dilated pupil [+light sensitivity], down and out eye
- can get it from posterior communicating artery aneurysm or other compressive lesion to 3rd nerve
Aneurysm of what artery would lead to 3rd nerve palsy?
posterior communicating artery
What is diabetic 3rd nerve palsy?
- due to ischemic lesion to nerve, lose nerve but spare pupil/pupilloconstrictor fibers that travel on outside of nerve
- get pain
- resolves in 4-6 wks
What part of oculomotor function is lost first in a compression related lesion?
parasympathetic [pupil constriction] lost first –> get dilated pupil and photosensitivity
- because parasympathetic fibers run on the outside of the nerve
What part of oculomotor function is spared in diabetic 3rd nerve palsy?
parasympathetic [pupil constriction] spared
- because parasympathetic fibers run on the outside of the nerve
What is the only cranial nerve that exits from dorsal aspects of brainstem?
trochlear nerve
What is the only cranial nerve to originate totally from the contralateral nucleus?
trochlear nerve
Which nerve has the longest intracranial course of all cranial nerve?
trochlear nerve
What are signs of trochlear lesion?
- affected high slightly elevated and extorted
- might see patient tilting head to normal side so both eyes can be at same angle
What is the largest cranial nerve?
trigeminal [CN V]
What are the 3 sensory nuclei of trigeminal nerve [and function of each]?
spinal trigeminal nucleus: pain, temperature, crude touch
pontine trigeminal/chief sensory nucleus: discriminative touch
mesencephalic nucleus: proprioceptions from muscles of mastication
Where is the motor nucleus for trigeminal?
in the pons, travels with mandibular division
Where does V1 [trigeminal opthalmic] leave?
leaves orbit through superior orbital fissure
Where does V2 [trigeminal maxillary] enter skull?
enters skull through foramen rotundum
Where does V3 [trigeminal mandibular] enter skull?
enters skull through foramen ovale
Which of the 3 trigeminal branches has motor output?
- all 3 have sensory
- only mandibular has motor as well
Where is the trigeminal ganglion?
meckel’s cave in pos
Where does trigeminal exit the brain?
- lateral surface of pons [large sensory root and smaller motor root emerge]
What is the trigeminal autonomic reflex?
- irritation of trigeminal leads to parasympathetic activation [eyes tear, nose run] because of close proximity of superior salivatory nucleus
What is trigeminal neuralgia? signs? cause?
- usually one sided V2 and V3 distribution
- repetitive, brief stabbing pains
- affects age 40+
- have trigger zones that cause electric pain when lightly touch
- symptoms occur only during day not during sleep
- due to vascular compression by looping SCA [superior cerebellar artery]
What is treatment for trigeminal neuralgia?
- antiepileptic drugs
- neurosurgery
What common virus can affect trigeminal ganglion?
- herpes zoster –> get herpes opthalmicus
What happens with CN V in brainstem lesion?
have ipsilateral pain/temp and sensory loss
What happens with CN V in cerebrum lesion?
have contralateral sensory loss
What is jaw jerk?
get problem with CNV3 [mandibular] –> issue with trigeminal motor, jaw deviates toward lesion side
What is so special about trigeminal nerve root entry zone?
- proximal trigeminal nerve root is sensitive to vascular compression since oligodendrocyte-derive myelination surrounds axons 3-5 mm from lateral pons
- not as sturdy as peripheral schwann myelin
- fibers associated with light touch are closest to this zone so most at risk
Where does CN VI emerge?
pons at pontomedullary junction
Where does CNVI enter the orbit?
via superior orbital fissure
What is sign of lesion at CN VI? Cause?
- diplopia [double vision] at a distance, medially directed eye
- likely due to increased ICP
Where does CN VII emerge?
- pons at pontomedullary junction
What is unique about upper motor neuron vs lower motor neuron supply for facial nerve?
- supply to upper facial muscles = bilateral
- supply to lower facial muscles = contralateral
thus: if injury to 1 of upper motor neurons [ex stroke], forehead muscles not affected, BUT contralateral lower face muscles will be affected
What happens if lower motor neuron lesion [damage to facial nerve itself or brainstem nucleus]?
- facial palsy on same side as lesion
- upper and lower parts of the face are affected
What are some common causes of facial nerve lesion?
- bell’s palsy
- meningeal process
- stroke involving nerve VII nuclesu
What happens if upper motor neuron lesion to facial nerve?
- contralateral lower facial paralysis
forehead spared due to bilateral innervation
What happens in bell’s palsy?
ipsilateral total facial paralysis
- drooping, teariness or dryness, pain in or behind ear, drooling, loss of sense of taste
Where does CN VIII exit?
medulla/pons junction, cerebellopontine angel
What causes hemifacial spasm?
- facial nerve compressed by dilated vertebral artery
What does gag reflex test?
- sensory component of IX
- motor component of X
What is glossopharyngeal neuralgia?
- stabbing pain in throat triggered by yawning/swallowing
- can be associated with bradycardia
What is eagle’s syndrome?
- lesion of nerve IX
- dysphagia [difficulty swallowing], unilateral pharyngeal pain with swallowing
What is sensorineural hearing loss?
hearing loss due to problem with CN VIII, inner ear, or central processing centers of brain
What is conductive hearing loss?
hearing loss due to problem with middle ear, tympanic membrane, or external ear
What happens in acoustic neuroma?
- loss of function of CN VIII (and sometimes CN VII as well)
Where does CN IX exit?
- upper medulla from post-olivary sulcus, dorso-lateral to olive
Where does CN X exit?
- medullar from post-olivary sulcus, dorso-lateral to olive
Where does uvula deviate in CNX lesion?
toward normal side [away from lesion]
What does glomus jugulare tumor affect? who gets it?
- affects IX, X, XI
- get pulsatile tinnitus
- most common in middle aged women
What are signs of CN XI lesion?
- weakness turing head to side contralateral to lesion
- shoulder droop ipsilateral to lesion
- compression by glomus jugulare tumor
Are the CN XI fibers supplying the trapezius or those supplying the sternocleidomastoid more vulnerable?
- those supplying trapezius are more vulnerable
Where does CN XII emerge?
- from medulla in area between pyramid and olive
What does CN XII innervate?
all intrinsic muscles except palatoglossus
How do you check for CN XII function?
- check for tongue protrusion in midline
- tongue will deviate to side of weakness [away from normal]
- check for slurred speech
What would happen in lower motor neuron lesion to CN XII?
- tongue deviates toward lesion, atrophy, fasciculations
- due to: damage to brainstem nucleus or hypoglossal nerve itself from tumors, surgery, amyotrophic lateral sclerosis
What would happen in upper motor neuron lesion to CN XII?
- tongue deviates away from lesion, no atrophy or fascicultations
- due to: cortical stroke or tumor
What is pseudobulbar palsy?
- bilateral damage to corticobulbar tracts [pathway from cortex to brainstem]
- symptoms: inability to control facial movements, impaired swallowing, spastic speech, random crying and laughing spells
- nerves V, VII, IX, X, XI, XII affeced
How do you treat pseudobulbar palsy?
dextromethorphan
