Vestibular Function Flashcards
What does the vestibular system function as?
accelerometer
What two reflexes does the vestibular system modulate and what do they do?
vestibular ocular reflex- keeps image focused in peripheral vision
vestibulospinal reflex- allows us to maintain postural stability
What occurs if the system sense constant velocity?
system shuts off since acceleration=0, can lead to misinterpretation of signals
What do the semicircular canals sense?
angular acceleration in x, y, z planes
What do the saccule and utricle sense?
inertial forces, gravitational forces and translational forces (up/down, side to side)
What is the output of the vestibular system proportional to?
velocity (integrates the acceleration information to send a velocity related signal to motor system)
What gives directional sensitivity in the vestibular system?
polarization of hair cells?
In what part of the semicircular canals do all the hair cells orient in the same direction?
ampulla
What does the striola do?
separates hair cells with opposite polarity
What directionalities are the sacculus and utricle associated with?
sacculus- vertical
utricle- horizontal
What is the otolithic membrane? What projects here? What is it covered with?
It is a gelatinous membrane that covers the hair cells and has the cilia of the hair cells projecting into it, otoconia (calcium carbonate crystals) lie on top of it to give weight to it
Which way is the displacement of the otolithic membrane and hair cells with reference to the inertial force?
opposite
What does a backwards sustained head tilt or transient forward acceleration cause?
depolarization of hair cells (towards kinocilia)
What does a forwards sustained head tilt or transient deceleration cause?
hyperpolarization of hair cells
Why are semicircular canals on either side of the head said to be paired?
They work together to give bilateral information about rotation
What is the cupula? Why is it important?
gelatinous membrane in the ampulla of the semicircular canals, gets displaced by inertia of fluid in canals due to angular accelerations or decelerations of head and puts shearing stress on hair cells
What vestibular nucleus is excited by left rotation? inhibited?
left vestibular nucleus is excited by left rotation, right is inhibited
What does vestibular nucleus activation cause?
excitation of the contralateral lateral rectus and via the mlf, the medial rectus of the ipsilateral eye
inhibition of the ipsilateral lateral rectus and via mlf, contralateral medial rectus
Which way do eyes rotate in response to right rotation?
to the left
What defines the direction of nystagmus? Which direction is this in compared to the rotation?
the fast resetting saccade, it is in the same direction as rotation (opposite the direction of the original eye movement)
What occurs in pathologic VOR?
there is no activity in one canal, so comparison between the 2 paired canals makes it appear as if you are rotating in the direction of the functional canal
will have slow eye movements towards the nonfunctional canal and fast resetting saccades towards the functional canal
What does the vestibulospinal reflex do if you think you’re rotating left due to pathologic VOR?
since you think youre rotating left, it will excite left extensor muscles to maintain postural balance so you don’t fall, and it causes you to stagger to the right
