Vestibular system Flashcards
functions of vestib system (3)
1) detect sensory stim that reflect rotation of head + head’s orientation with resp to gravity
2) contrib to sense of balance + vision + proprioception + tactile
3) allow eye to remain steady during head motion
2 sensory receptors in inner ear
2 pairs of otolith organs (utricle, saccule)
3 pairs of semicircular canal (ant, post, horizontal 90degr apat and situated at 45degr)
fxns of otolith organs
fxn = detect linear acceleration (change in velocity) and direction of gravity vector
fxns of semicircular canal
detect head rotation = angular acceleration = simultaneous change in velocity and direction
hair cells convert ___ to ___
convert motion stim into electrical signal
name of single longest stereocilia on one side of bundle
each stereocilia connected by ___
kinocilium
connected by hair-like fiber = tip link
what happens when hair cell bends towards kinocilium
1) pulls on tip link
2) open K+ channel at ip
3) K+ enter and hair cell depol
4) open Ca2+ channel at base
5) Ca2+ enter –> release NT and afferent nerve fires AP at higher freq
what happens when hair cell bends away from kinocilium
1) brings tips of cilia closer together
2) tip link relax
3) close K+ channel
4) hyperpol
what is macula
disc like thick membrane in saccule and utricle along wall of each sac
contains hair cells as sensory apparatus
what is otoconia
fxn
sticky CaCO3 crystals with greater density than surround fluid adhere to macula for extra mass to load on hair cell cilia
allows sense of changing orientation of hair cell in resp to gravity
utricle and saccule relation to each other
utricle lies ___
saccule lies
direction fo hair bundles
90 degr apart
utricle = horizontal on floor with hair bundles vertical
saccule = hangs vertically from lateral wall with hair bundles horiz
utricle
tilt of head from horiz causes
tells brain?
causes shear btwn hair cells and overlying otolithic membrane
–> tells brain tilt horiz and linear accel in horiz plane (acceleration in vehicle)
saccule
vertical movemnt of head causes
tells brain?
causes shear from relative inertia of otolithic membrane
tells brain direction of gravity and linear accel in vertical direction (accel and decel in elevator)
axis of polarity of hair cells in each otolith organ is ___
utricle patch
saccule patch
not uniform
hair cells form 2 broad patches
utricle = cilia in each patch oriented toward curving central stripe = striola to optimize excitatory signal
saccule = cilia in each patch orient away from striola
ends of semicircular canal
what is inside each end?
projects to?
ends = swelling = ampulla
inside = ridge of sensory epith = crista that connects hair cells
projet to gelatinous mass = cupula
cupula bisects what?
what happens when cupula deflected
bisects bulge of ampulla
all hair cell in crista will respond identical
axis of polarity in each crista
hair cells have same axis with kinocilium on same side of each hair cell bundle
horizontal canal
hair cells oriented in relation to kinocilium
stim by?
fluid flows how?
oriented with kinocilia facing side of ampulla nearest utricle
stim by ampullapetal movement
fluid flows along limb of semicrcular canal towards ampulla and utricle
anterior and posterior canal
hair cells oriented in relation to kinocilium
stim by?
fluid flows how?
kinocilia face side of ampulla that opens in arm of semicrcular canal and away from utricle
stim by ampullofugal movement
fluid flow away from utricle and ampulla
deflection of cupula triggers
bending of hair cell stereocilia
depol hair cell
what happens when head moves right (5 steps)
1) fluid in right horiz canal moves left relative to cupula due to inertia
2) hair cell in right horiz canal crista depol
3) cupula deflect in ampullapetal direction
4) incr afferent firing of nerves in right horiz canal crista
5) in left ampulla hair cell hyperpol and afferent AP freq decr
why can each horiz canal detect movement to right and left
baseline firing rate that incr or decr in each canal
what happens when head rotation continues at constant velocity
what happens when head stop
continued head rotation = endolymph catch up with head –> cupula not deflected
head stop = endolymph keep moving for brief time
cupula deflect again but opposite to beginning of head rotation
vestibulo-ocular reflex
function
allows eyes to maintain focus on point of interest with head movement
mechanism of vestibulo-ocular reflex
as inner ear sense head rotation, signal sent to MLF, then to abducens, trochlear, oculomotor nuclei
causes eyes to move in opposite direction of head move so eye steady
vestibulo-colic reflex function
maintain head stability and upright stance of head
mechanism of vestibulo-colic reflex
vestib system senses direction of gravity and initiate motor reflex in muscles controlling head and neck
vestibulo-spinal reflex function
assist balance and framework for coord motion of limbs during ambulation
mechanism of vestibulo-spinal reflex
in response to gravity
righting reflexes
in response to gravity, VSR maintiains muscle tone to prime framework for muscle action
when human push to one side, limb of half of body extend while opposite flex to rebalance
