VII-Vestibular Function Flashcards
functions
- integrate senosry info/motor resp
- body position/move
- postural tone
- stabilze eyes during head move
- automatic behavior and perception
groups of vestibular organs
- otolith organs - utricle + saccule
- semicircular canals (anterior, posterior, horizontal)
otolith organ function
linear movement + orientation to gravity
site of signal transduction otolithic
maculae (utricle and saccule) with hair cells
semicircular function
rotational movement
site of signal transduction semicircular
ampullae
chemical comp of endolymph
high K (150)
low Na (16)
opposite of normal extracellular fluid
hair cell structure
tall kinocillium + shorter stereocilia connected by filaments
firing of hair cells
activation of hair cells inc firing
-direction is towards the kinocilium
opposite direction movement dec firing rate
maculae structure
gelatinous layer for hair cells to project into + otoconia crystal layer
types of displacements
- static- aka tilting back or forward, back activates hair cells, forward deactivates
- transient- aka acceleration or deceleration, accel activates and decel deactivates
depolarization of signal transduction
- movement of cilia activates mechanically gated K+ channels
- endolymph/K+ influx depolarizes hair cell by activate voltage gated Ca channels
- Ca enty stims transmitter release
- nerve impulse generated
pairs of canals
- both horizontals
- R anterior + L posterior
- L anterior + R posterior
so any direction of movement can be detected
ampulla structure
- crista - sensory epithelium
- cupula - gelatinous mass for supporting hair cells and block endolymph
- all hair cells/kinocilia point in same direction
endolymph movement horizontal ampulla
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
firing rate of ampulla in rotation
- initial spike in firing from cupula deflected in acceleration of rotation
- fall to baseline during constant rotation/return to non deflected state
- drop during deceleration when cupula deflected in oppo direction
- return to baseline
vestibular ocular reflex
move eyes in resp to small head turns aka stabilize eyes by eyes moving opposite direction of head turn
oculomotor nucleus controls
nasal extraocular muscles
abducens nucleus controls
lateral extraocular muscles
inhibition of abducens N
by vestibular nucleus
physiologic nystagmus
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
spontaneous nystagmus
loss of VOR reflex so difficult to fixate while head is turning
-get nystagmus without head movement
caloric testing
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
COWS
cold water nystagmus opposite
warm water nystagmus same side
only for fast phase
BPPV
common type of vertigo @ post semicanal
-from free floating otoconia OR otoconia attached to cupula = short episodes of virtigo
Dix Hallpike Maneuver
to diagnose virtigo thru otoconia movement
treat with Epley manuever
menieres syndrome
episodic vertigo up to hours+ hearing loss, tinnitus, aural pressure
from inc endolymph fluid > rupture labrynth membranes and mix endo/perilymph
