L30 Vestibular system

Question 1

What are hair cells?

Answer 1

receptor cells of the vestibular and cochlear division of the inner ear

Question 2

what are the hair cells responsible for?

Answer 2

transducing mechanical stimuli into neuronal stimuli onto the afferent fibers of CN 8 Vestibulocochlear n.

Question 3

what does the apex of hair cells contain?

What are they surrounded by

Answer 3

sterocilia

endolymph

Question 4

there is a high concentration of ___ in the endolymph which is essential for signal transduction process

Answer 4

K+

Question 5

Describe the mechanism behind the depolarization/hyperpolarization of hair cells

Answer 5

-mechanical force from endolymph against hair cells will open/close the TRPA-1 channels causing depolarization or hyperpolarization

Question 6

what is the “tip link”? Explain what happens when the tip link is opened.

Answer 6

they are between the stereocilia of hair cells and they directly open the hatch on top of the TRPA-1 channel causing K+ influx = depolarize the hair cell => opening of calcium-gated channels=> Ca2+ influx = NT release on CN 8 (afferent) causing a full action potential!

Question 7

what type of potentials do hair cells have

Answer 7

graded potentials

Question 8

the frequency of AP _____ as the graded potential of the hair cells ___

Answer 8

increase

increase

Question 9

what are the 2 otopith organs

Answer 9

saccule and utricle

Question 10

describe the otolith organs (saccule and utricle)

Answer 10

endolymph filled pockets whose walls are lines with hair cells

Question 11

what do otolith organs detect?

Answer 11

linear acceleration

Question 12

what is the purpose of the hair cell cilia and kinocilium having alternating oritentations relative to the stiola

Answer 12

allows a single sitmulus to activate one group and inhibit the other group at the same time

Question 13

what is kinocilium?

Answer 13

the largest cilium

Question 14

what happens if the cilia are tilted away form the kinocilium

Answer 14

inhibits causing a decrease in NT release and decreasing AP frequency relative to neutral position

Question 15

what happens if the cilia are tilted towards form the kinocilium

Answer 15

excites causing an increase in NT release and increasing AP frequency relative to neutral position

Question 16

what are semicircular canals?

Answer 16

endolymph filled pipes whose walls are lined with hair cells

Question 17

what can semicircular canals detect

Answer 17

angular acceleration

Question 18

when endolymph move relative to the walls of the canal (like when the head spins) it causes the cilia to bend which deduces?

Answer 18

angular acceleration

Question 19

what happens to the capula/cilia when hte semicircular canal (and head) rotate to the left?

Answer 19

bend to the right = excitation or inhibition

Question 20

the endolymph in the semicircular canal is _____

Answer 20

delay - think of water spinning in a bottle, it takes time to reach the speed of the wall of the bottle

Question 21

the vestibular system works largely at a ____ level, thus there is NO primary vestibular cortex area

Answer 21

subconscious

Question 22

what is the basic vestibular pathway

Answer 22

• input from vestibular system
• input uses CN 8
• to vestibular nuclei
• output sent to cerebellum, motor neurons of the limbs, back and neck, motor neurons controlling extraocular muscles (important for VOR)

Question 23

explain the Vestibuloocular reflex?

Answer 23

head rotation to the L
endolymph flow to R
excitation in L - pushed back
inhibition in R - pushed forward

Question 24

what is nystagmus

Answer 24

alternating smooth pursuit in one direction followed by a saccadic movement in other direction
slow phase - driven by reflex circuitry
fast phase - reset mechanism driven by saccadic circuitry

*physiologica vs. pathological

Question 25

what is vestibulo-ocular nystagmus

Answer 25

physio nystagmus induced by continous rotation of the endolymph (and head?)
endolymph flow activates VOR
if stimulus is persistant - eyes flips back and forth

Question 26

what is the slow phase

Answer 26

drive by reflex

when eyes swing in opposite direction of head spin

Question 27

what is fast phase

Answer 27

driven by saccadic circuitry

eyes reset after reaching max gaze

Question 28

what is occulocephalic Maneuver (doll’s eye maneuver)

Answer 28

examiner forceibly turns head of pt and looks to see if the COR is intact
should work in comatose pts as well

Question 29

what is caloric testing of VOR

Answer 29

place cold water in ear of pt which changes the density of the endolymph and induces a spin
cold water - makes endolymph sink = inhibiting that side ( put water in R ear, would cause rxn as if head was spinning to the L) = OPPOSITE

warm water - makes endolymph float, exciting the side (put was in R ear, would cause a rxn as if head was spinning to the R) = SAME

Question 30

what is Meniere’s disease

Answer 30

abnormalities of the endolymph circulation caused by dilation of the endolymph compartment and degen of hair cells

symptoms - sudden and recurrent vertigo attacks

Question 31

motions sickness cause

Answer 31

caused by discrepancy between the vestibular and visual inputs

Question 32

why do you get the spins with alcohol intoxication

Answer 32

alcohol interacts with endolymph and induces abnormal spinning of the endolymph similar to that seen in the caloric testing of the VOR

Question 33

what is the effect of antibiotics on vestibular system

Answer 33

can be toxic to hair cells - can accumulate in endolymph

Question 34

describe pathological vestibular nystagmus

Answer 34

cause by damage to one side of the vestibular system (canal OR CN8)
will induce slow phase towards side with damage labyrinth and fast phase toward normally functioning side
will persist as this pathological stimulus also persists