Vestibular system

Question 1

functions of vestib system (3)

Answer 1

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

Question 2

2 sensory receptors in inner ear

Answer 2

2 pairs of otolith organs (utricle, saccule)

3 pairs of semicircular canal (ant, post, horizontal 90degr apat and situated at 45degr)

Question 3

fxns of otolith organs

Answer 3

fxn = detect linear acceleration (change in velocity) and direction of gravity vector

Question 4

fxns of semicircular canal

Answer 4

detect head rotation = angular acceleration = simultaneous change in velocity and direction

Question 5

hair cells convert ___ to ___

Answer 5

convert motion stim into electrical signal

Question 6

name of single longest stereocilia on one side of bundle

each stereocilia connected by ___

Answer 6

kinocilium

connected by hair-like fiber = tip link

Question 7

what happens when hair cell bends towards kinocilium

Answer 7

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

Question 8

what happens when hair cell bends away from kinocilium

Answer 8

1) brings tips of cilia closer together
2) tip link relax
3) close K+ channel
4) hyperpol

Question 9

what is macula

Answer 9

disc like thick membrane in saccule and utricle along wall of each sac

contains hair cells as sensory apparatus

Question 10

what is otoconia

fxn

Answer 10

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

Question 11

utricle and saccule relation to each other

utricle lies ___
saccule lies

direction fo hair bundles

Answer 11

90 degr apart

utricle = horizontal on floor with hair bundles vertical

saccule = hangs vertically from lateral wall with hair bundles horiz

Question 12

utricle
tilt of head from horiz causes

tells brain?

Answer 12

causes shear btwn hair cells and overlying otolithic membrane

–> tells brain tilt horiz and linear accel in horiz plane (acceleration in vehicle)

Question 13

saccule
vertical movemnt of head causes

tells brain?

Answer 13

causes shear from relative inertia of otolithic membrane

tells brain direction of gravity and linear accel in vertical direction (accel and decel in elevator)

Question 14

axis of polarity of hair cells in each otolith organ is ___

utricle patch

saccule patch

Answer 14

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

Question 15

ends of semicircular canal

what is inside each end?

projects to?

Answer 15

ends = swelling = ampulla

inside = ridge of sensory epith = crista that connects hair cells

projet to gelatinous mass = cupula

Question 16

cupula bisects what?

what happens when cupula deflected

Answer 16

bisects bulge of ampulla

all hair cell in crista will respond identical

Question 17

axis of polarity in each crista

Answer 17

hair cells have same axis with kinocilium on same side of each hair cell bundle

Question 18

horizontal canal
hair cells oriented in relation to kinocilium

stim by?

fluid flows how?

Answer 18

oriented with kinocilia facing side of ampulla nearest utricle

stim by ampullapetal movement

fluid flows along limb of semicrcular canal towards ampulla and utricle

Question 19

anterior and posterior canal
hair cells oriented in relation to kinocilium

stim by?

fluid flows how?

Answer 19

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

Question 20

deflection of cupula triggers

Answer 20

bending of hair cell stereocilia

depol hair cell

Question 21

what happens when head moves right (5 steps)

Answer 21

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

Question 22

why can each horiz canal detect movement to right and left

Answer 22

baseline firing rate that incr or decr in each canal

Question 23

what happens when head rotation continues at constant velocity

what happens when head stop

Answer 23

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

Question 24

vestibulo-ocular reflex

function

Answer 24

allows eyes to maintain focus on point of interest with head movement

Question 25

mechanism of vestibulo-ocular reflex

Answer 25

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

Question 26

vestibulo-colic reflex function

Answer 26

maintain head stability and upright stance of head

Question 27

mechanism of vestibulo-colic reflex

Answer 27

vestib system senses direction of gravity and initiate motor reflex in muscles controlling head and neck

Question 28

vestibulo-spinal reflex function

Answer 28

assist balance and framework for coord motion of limbs during ambulation

Question 29

mechanism of vestibulo-spinal reflex
in response to gravity

righting reflexes

Answer 29

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