5.8 Vestibular Flashcards
quick step changes in eye position as the visual field is scanned, up to 400-700 degrees/second
saccades
during saccades there is no blurring of visual field because _______ is too fast for neurons to respond, and the ________ is inhibited (corollary discharge)
velocity, lateral geniculate nucleus
neural path for what type of saccades?
frontal eye field (area 8) –> superior colliculus –> reticular formation –> oculomotor nuclei –> eye muscle –> saccade
neural pathway for voluntary saccades
neural path for what type of saccades?
novel stimuluts –> retinal ganglion cells –> superior colliculus –> reticular formation –> oculomator nuclei –> eye muscle –> reflex saccade
reflex/triggered saccades
tracking movements, up to 30 degrees/second
smooth pursuit
neural path for what type of eye movement?
retinal slip of image on retina –> retinal ganglion cells –> lateral geniculate nucleus –> visual cortex –> reticular formation –> oculomotor neurons -> eye muscles –> movement
smooth pursuit
maintain fixation in presence of head movement, up to 300 degrees per second
vetibulo-ocular reflex (VOR)
adequate stimulus for kinetic labyrinth (semicircular canals)?
dynamic stimuli (rotational forces) or head acceleration/deceleration
adequate stimuli for static labyrinth (otolith organs, utricle, saccule)?
static stimuli, maintained head position (tilit); transitional forces, horizontal displacement
viscous fluid filling the canals and otolith organs, continuous with utricle through the canal
endolymph
enlargement at one end of a semicircular canal, within it are vestibular hair cell receptors
ampulla
gelatinous mass into which the cilia of the hair cells insert
cupulla
hair cells synapse with the terminals of _____ axons from CN 8, cell bodies form _______ ganglion
afferent, Scarpa’s
simple long cilium
kinocilium
multiple smaller cilia
stereocilia
bending cilia toward the ________ produces _______ of the hair cell and an increase in firing rate of 8th nerve afferent
kinoclium, depolarization
bending cilia away from the _______ produces _________ of the hair cell and a decrease in firing rate of the 8th nerve afferent
kinocilium, hyperpolarization
adequate stimulus for semicircular canal receptors is ________
head rotation
due to inertia, endolymph will tend to move in the direction ______ rotation
opposite
subject is rotated in a chair, chair is stopped and vestibular function is examined by observing VOR and vestibulopostural reflexes, effects of deceleration are examined
barany chair test
acceleration to the right (rotational phase) would _______ in right 8th nerve activity, and ______ in left 8th nerve activity
increase, decrease
rotation at constant angular velocity has no effect after about 30 seconds because endolymph has _________
equilibrated
deceleration (post rotational phase) has _______ in right 8th nerve activity and _______ in left 8th nerve activity
decrease, increase
involuntary back and forth, up and down, or rotating movement of eyeballs, with a slow pull and rapid return jerk
nystagmus
a lesion will cause subject to fall ______ side of lesion and have nystagmus on _______ side
toward, opposite
in right rotational phase, increase in CN8 actiivty –> activation of right (flexors or extensors?) and decreased CN8 activity on the left inhibits left _______ –> will fall to the _______
extensors, extensors (flexion), left
in right post-rotational (deceleration) phase, decreased CN8 activity leads to inhibition of right _____, and increased CN8 activity on the left leads to _________, therefore patient will fall to _______
extensors (flexion) , extension, right
caloric stimulation test: irrigation with warm water causes ________ nystagmus, irrigation with cold water causes _______ nystagmus
same side, opposite, (COWS)
in unilateral lesions of CN VIII, the patient falls (toward or away?) side of lesion, and get nystagmus to (same or opposite side?)
toward lesion, opposite nystagmus
