VII-Vestibular Function

Question 1

functions

Answer 1

1. integrate senosry info/motor resp
2. body position/move
3. postural tone
4. stabilze eyes during head move
5. automatic behavior and perception

Question 2

groups of vestibular organs

Answer 2

1. otolith organs - utricle + saccule
2. semicircular canals (anterior, posterior, horizontal)

Question 3

otolith organ function

Answer 3

linear movement + orientation to gravity

Question 4

site of signal transduction otolithic

Answer 4

maculae (utricle and saccule) with hair cells

Question 5

semicircular function

Answer 5

rotational movement

Question 6

site of signal transduction semicircular

Answer 6

ampullae

Question 7

chemical comp of endolymph

Answer 7

high K (150)
low Na (16)

opposite of normal extracellular fluid

Question 8

hair cell structure

Answer 8

tall kinocillium + shorter stereocilia connected by filaments

Question 9

firing of hair cells

Answer 9

activation of hair cells inc firing
-direction is towards the kinocilium
opposite direction movement dec firing rate

Question 10

maculae structure

Answer 10

gelatinous layer for hair cells to project into + otoconia crystal layer

Question 11

types of displacements

Answer 11

1. static- aka tilting back or forward, back activates hair cells, forward deactivates
2. transient- aka acceleration or deceleration, accel activates and decel deactivates

Question 12

depolarization of signal transduction

Answer 12

1. movement of cilia activates mechanically gated K+ channels
2. endolymph/K+ influx depolarizes hair cell by activate voltage gated Ca channels
3. Ca enty stims transmitter release
4. nerve impulse generated

Question 13

pairs of canals

Answer 13

1. both horizontals
2. R anterior + L posterior
3. L anterior + R posterior

so any direction of movement can be detected

Question 14

ampulla structure

Answer 14

1. crista - sensory epithelium
2. cupula - gelatinous mass for supporting hair cells and block endolymph
3. all hair cells/kinocilia point in same direction

Question 15

endolymph movement horizontal ampulla

Answer 15

turn head one direction- endolymph flows other way
i.e. turn head left endolymph flows right in R side ampulla/inc firing, L side endolymph flows away from hair cells so dec firing

Question 16

firing rate of ampulla in rotation

Answer 16

1. initial spike in firing from cupula deflected in acceleration of rotation
2. fall to baseline during constant rotation/return to non deflected state
3. drop during deceleration when cupula deflected in oppo direction
4. return to baseline

Question 17

vestibular ocular reflex

Answer 17

move eyes in resp to small head turns aka stabilize eyes by eyes moving opposite direction of head turn

Question 18

oculomotor nucleus controls

Answer 18

nasal extraocular muscles

Question 19

abducens nucleus controls

Answer 19

lateral extraocular muscles

Question 20

inhibition of abducens N

Answer 20

by vestibular nucleus

Question 21

physiologic nystagmus

Answer 21

reflex to move eyes in resp to small head turns
-slow movement counters/oppo head turn, mediated by VOR
-fast saccade resets eye position when far excursion reached

Question 22

spontaneous nystagmus

Answer 22

loss of VOR reflex so difficult to fixate while head is turning
-get nystagmus without head movement

Question 23

caloric testing

Answer 23

unconscious patient’s vestibular system tested/integrity of brainstem
-supine + head tilted forward so that horizontal canal is vertical

warm water in one ear causes endolymph to rise and activate hair cells = head turn oppo slow phase
cold water in other ear endolymph sinks so dec firing = same side slow phase

Question 24

COWS

Answer 24

cold water nystagmus opposite
warm water nystagmus same side

only for fast phase

Question 25

BPPV

Answer 25

common type of vertigo @ post semicanal
-from free floating otoconia OR otoconia attached to cupula = short episodes of virtigo

Question 26

Dix Hallpike Maneuver

Answer 26

to diagnose virtigo thru otoconia movement

treat with Epley manuever

Question 27

menieres syndrome

Answer 27

episodic vertigo up to hours+ hearing loss, tinnitus, aural pressure

from inc endolymph fluid > rupture labrynth membranes and mix endo/perilymph