Cranial Nerves Flashcards
General Info on CN
12 that originate from brain stem (medulla, pons, midbrain)
sensory functions (1, 2, 8)
motor functions (3, 4, 6, 11, 12)
mixed functions (5, 7, 9, 10)
mnemonics
on - olfactory
occasion - optic
our - oculomotor
trusty - trochlear
truck - trigeminal
acts - abducens
funny - facial
very - vestibulocochlear
good - glossopharyngeal
vehicle - vagus
any - accessory (spinal)
how - hypoglossal
some - sensory
say - sensory
marry - motor
money - motor
but - both
my - motor
brother - both
says - sensory
big - both
brains - both
matter - motor
more - motor
CN I - Olfactory
projects from olfactory regions to mid-brain
smell, only uncrossed sense
each nostril tested independently, occlude one and ask to identify scent in other
anosmia (olfactory loss) happens with sub frontal masses (tumor, abscesses), trauma in orbitofrontal region where nerve penetrate cribriform plate of ethmoid, viral infections with damage to factory neuroepithelium
CN II - Optic
projects from retina to midbrain
vision
the 2 optic nerves meet at optic chasm
visual fields assessed by having pt look in examiner’s eye and identify peripheral finger motion
abnormality in optic chiasm causes visual temporal field loss (bitemporal hemianopsia)
postchiasmic lesions result in loss of half of contralateral visual hemifield on same side in both eyes (homonymous hemianopsia)
prechiasmic lesions lead to monocular blindness
involvement in optic radiations in posterior temporal lobe (Meyer’s loop) results in superior quadrant visual field on contralateral side (homonymous superior quadrantanopsia)
involvement of optic radiations in parietal lobe can lead to loss of inferior quadrant visual field on contralateral side (homonymous inferior quadrantanopsia)
abnormality in optic chiasm
causes visual temporal field loss (bitemporal hemianopsia)
postchiasmic lesions
result in loss of half of contralateral visual hemifield on same side in both eyes (homonymous hemianopsia)
prechiasmic lesions
lead to monocular blindness
involvement in optic radiations in posterior temporal lobe (Meyer’s loop)
results in superior quadrant visual field on contralateral side (homonymous superior quadrantanopsia)
involvement of optic radiations in parietal lobe
can lead to loss of inferior quadrant visual field on contralateral side (homonymous inferior quadrantanopsia)
CN III - Oculomotor
originates from midbrain and projects to extraocular muscles except oblique and lateral rectus
assessed by observing eye movements and shining light to pupil
responsible for eye movement medially (adduction), inferiorly, superiorly. it also includes Pupi constriction due to parasympathetic fibers to pupillary constrictor muscles
compression here from aneurysm or uncle herniation can lead to fixed dilated pupil (blown pupil); significant pupillary compression (pinpoint pupil) can mean pontine involvement or drug overdose (morphine)
CN IV - Trochlear
CN VI - Abducens
trochlear originates from midbrain and projects to superior oblique muscles
abducens originates from pons, projects to lateral rectus muscle
both evaluated by observing vertical and lateral eye movements
compression of trochlear can happen with cerebellar tumors or damage to shear injury from head trauma; leads to vertical diplopia (suppression of eye)
compression of abducens can happen with elevated ICP and leads to horizontal diplopia (failure to adduct)
CN V - Trigeminal
originates from pons and innervates upper, middle, lower portions of the face via ophthalmic, maxillary, mandibular divisions
provides sensory innervation to face, nasal sinuses, mouth, anterior 2/3 of tongue and controls muscles for chewing
tested by assessing facial sensation, corneal reflexes, jaw jerk reflexes
CN VII - Facial
originates from lower pons and upper medulla
controls muscle for facial expression, parasympathetic (tears and salivation), visceral sensory (taste), general somatosensory
assessed by looking for asymmetry in spontaneous facial expressions
unilateral UMN lesions spare the forehead
facial droop following stroke involves mouth/lower face sparing the forehead and involvement of forehead implies lesion in this CN
LMS lesions can result in contralateral forehead denervation
CN VIII - vestibulocochlear
projects from auditory canal to pontomedullary junction
responsible for auditory and vestibular fnx
tested with the rinne test, vibrating tuning fork placed just outside each ear to assess air conduction and on forehead or mastoid to assess bone conduction
sensorineural hearing loss caused by dysfunction here, air conduction remains greater than bone conduction (normal) and sound laterializes to normal ear
conductive hearing loss caused by external auditory canal or middle ear abnormalities, detected when bone conduction is better than air conduction
vestibular functions tested with dix-hallpike maneuver, can differentiate from central causes of vertigo - examiner supports pt’s head as they lie back on exam table and head is rotated
vertigo with nystagmus suggest dysfunction here
CN IX - glossopharyngeal
stems from medulla and projects to pharynx, middle ear, posterior tongue
general somatic sensory including touch, pain, temperature
evaluated by inducing gaga reflex
unilateral nerve dysfunction results in retraction to stronger side
