Vestibular Function

Question 1

What does the vestibular system function as?

Answer 1

accelerometer

Question 2

What two reflexes does the vestibular system modulate and what do they do?

Answer 2

vestibular ocular reflex- keeps image focused in peripheral vision
vestibulospinal reflex- allows us to maintain postural stability

Question 3

What occurs if the system sense constant velocity?

Answer 3

system shuts off since acceleration=0, can lead to misinterpretation of signals

Question 4

What do the semicircular canals sense?

Answer 4

angular acceleration in x, y, z planes

Question 5

What do the saccule and utricle sense?

Answer 5

inertial forces, gravitational forces and translational forces (up/down, side to side)

Question 6

What is the output of the vestibular system proportional to?

Answer 6

velocity (integrates the acceleration information to send a velocity related signal to motor system)

Question 7

What gives directional sensitivity in the vestibular system?

Answer 7

polarization of hair cells?

Question 8

In what part of the semicircular canals do all the hair cells orient in the same direction?

Answer 8

ampulla

Question 9

What does the striola do?

Answer 9

separates hair cells with opposite polarity

Question 10

What directionalities are the sacculus and utricle associated with?

Answer 10

sacculus- vertical

utricle- horizontal

Question 11

What is the otolithic membrane? What projects here? What is it covered with?

Answer 11

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

Question 12

Which way is the displacement of the otolithic membrane and hair cells with reference to the inertial force?

Answer 12

opposite

Question 13

What does a backwards sustained head tilt or transient forward acceleration cause?

Answer 13

depolarization of hair cells (towards kinocilia)

Question 14

What does a forwards sustained head tilt or transient deceleration cause?

Answer 14

hyperpolarization of hair cells

Question 15

Why are semicircular canals on either side of the head said to be paired?

Answer 15

They work together to give bilateral information about rotation

Question 16

What is the cupula? Why is it important?

Answer 16

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

Question 17

What vestibular nucleus is excited by left rotation? inhibited?

Answer 17

left vestibular nucleus is excited by left rotation, right is inhibited

Question 18

What does vestibular nucleus activation cause?

Answer 18

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

Question 19

Which way do eyes rotate in response to right rotation?

Answer 19

to the left

Question 20

What defines the direction of nystagmus? Which direction is this in compared to the rotation?

Answer 20

the fast resetting saccade, it is in the same direction as rotation (opposite the direction of the original eye movement)

Question 21

What occurs in pathologic VOR?

Answer 21

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

Question 22

What does the vestibulospinal reflex do if you think you’re rotating left due to pathologic VOR?

Answer 22

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