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Neurology > Physiology Auditory and Vestibular System > Flashcards

Physiology Auditory and Vestibular System Flashcards

1
Q

what makes up hair cells

A

stereocillia which vary in length

kinocillum which marks the orientation

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2
Q

how do hair cells create action potentials

A

Tips of sterocilia; potassium (TMC1) channels which are maximally open when the hair cell tilts in one direction and maximally closed when the hair cell tips in the other direction
Entry of potassium has consequences, will generate the depolarisation of hair cell allowing hair cell to release glutamate. Glutamate will act on efferent nerve endings

cell body releases glutamate onto efferent nerve endings which allows modulation of AP frequency in response to stimulus

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3
Q

what do the otolith organs sense

A

tilt and acceleration

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4
Q

what determines the pitch of sound

A

frequency

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5
Q

what determines the volume of sound

A

amplitude

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6
Q

what are the steps between sound being produced and us hearing it

A

Sound = vibration of air
= vibrate the eardrum, the malleus, the incus, and the stapes
= the vibration spreads to the cochlea.
= vibration of air is converted to movement/vibration of fluids in the cochlea
= the vibration in the cochlea is captured by hair cells
= transduction (physical vibration is transduced to neural energy)
= Perceived in the auditory cortex

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7
Q

how does the middle ear amplify sound

A

3 methods:

  • area ratio of ear drum to stapes foot plate (20:1)
  • lever action of ossicles
  • buckling of ear drum (causes a sound pressure increase)
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8
Q

what does reissners membrane do

A

separates scala vestibuli and scala media

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9
Q

what does the basilar membrane do

A

separates scala media from scala tympani

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10
Q

what part of cochlea goes into round window (how sounds leaves cochlea)

A

scala tympani

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11
Q

what part of coclea recieves input from oval window

A

scala vestibuli

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12
Q

what connects the scala vestibuli and tympani

A

the helicotrema

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13
Q

what is responsible for transduction in the coclea

A

organ of corti hair cells
basilar membrane
tectorial membrane

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14
Q

is the perilymph in the scala tympani and vestibuli continuous

A

yes

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15
Q

what fluid is in the scala media

A

endolymph

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16
Q

what structure allows us to discriminate pitch and how

A

basilar membrane
-is felxible an vibrates in sync with fluid motion - high pitched sounds move base of membrane, low pitches move the B< at the apex of the cochlea

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17
Q

where hair cells located

A

in organ of corti, between basilar membrane and reticular lamina- their tips are in the tectorial membrane

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18
Q

where do hair cells synapse

A

on bipolar neurones with cell bodies in the spiral ganglion

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19
Q

what membrane must vibrate for hair cells to move

A

tectorial (where the hair cells have their tips)

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20
Q

do all hair cells respond to the same sound

A

no hair cells are tuned to different frequencies

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21
Q

what liquids in ear have highest potassium concentration- what does this mean

A

higher K+ conc in endolymph (tips of hair cells in endolymph, when channel open when moved potassium will enter the cell through the potassium channel and cell will depolarise)

22
Q

what causes a hair cell to depolarise or hypoerpolarise

A

Displacement of the hair bundle toward the tallest stereocilia depolarizes the hair cell, while movements parallel to this plane toward the shortest stereocilia cause hyperpolarization.

23
Q

what state is the hair cell in at rest

A

slightly depolarised

24
Q

mutations in what channels can cause inherited forms of deafness

A

potassium channels, can recycle the ion

25
Q

what is the different innervation of the outer and inner hair cells

A

outer hair cells- get efferent inputs (control stiffness, amplify membrane vibration)

inner hair cells- afferent to CN VIII via cochlear nucleus, perception of sound

26
Q

what is the cochlear amplifier

A

outer hair cells outnumber inner hair cells
OHC respond to sound with a receptor potential AND a change in length (done by motor protein prestin)
this changes spatial relationship between basilar mem and tectorial mem
modulates responsiveness of auditory system

27
Q

how does furosemide affect cochlear

A

inactivates membrane motor of outer hair cells

28
Q

what are the auditory nerves two mechanisms for frequency coding

A 
place code (firing rate of neurones- important in sensitivity of hearing, low level sounds)
temporal code (times at which these firings occur- important in identifying onset and offset of the sounds)
29
Q

what is the central pathway of the auditory system

A

organ of corti
spiral ganglion
axons form cochlear nerve
joins with vestibular nerve
internal acoustic meatus
enters brainstem at cerebellopontine angle
cochear nuclei (info sent to both ventral and dorsal nuclei)

from dorsal CN- most fibres cross midline and ascend in the contralateral lateral lemniscus (others in ipsilateral lateral lemniscus)

from ventral CN- some fibres ascend in the lateral lemniscus bilaterally but most decussate to the contralateral superior olivary nuclei (in trapezoid body) (some fibres synapse in ispislateral superior ON)
this then projexts upwards into lateral lemniscus

as both dorsal and ventral nuclei have some fibres that decussate and some who dont, info from both ears travels bilaterally

both sides then reach inferior colliculus
then projects to ipsilateral medial (music goes medial) geniculate body
(in thalamus)

then project to primary auditory cortex (superior temporal gyrus, under lateral fissure)

30
Q

what are the two components of the auditory pathway

A

primary (lemniscal) pathway- main pathway through which auditory information reaches the primary auditory cortex

non lemniscal pathway- unconscious perception (attention, emotional response, auditory reflexes)

31
Q

what is tonotopy

A

spatial arrangement where sounds of different frequency are processed in the brain
(achieved as branches of CN VIII go to three cochlear nuclei: dorsal, posteroventral, anteroventral)

32
Q

what is responsible for locating the sound source in space

A

superior olivary nucleus- computes sound arrival at the two ears (ipsilateral earlier than contra)

33
Q

what forms a full spatial sound map

A

inferior colliculus

34
Q

what is repsonsible for indifying and pocessing complex sounds

A

the primary auditory cortex

35
Q

how does the supeiror olive nucleus determine differences in sound between ears

A

each SO neuron gets a depolarizing (from ipsilateral ear) and hyperpolarizing (from contralateral ear) signal
(inhibition from other ear)
determines the net excitation forwarded to inferior colliculus

36
Q

what are the roles of the vestibular system

A

provides information on gravity, rotation, acceleration
is a reference for the somatosensory and visual systems
allows for gaze, postural stability, sense of orientation, direction of linear and angular acceleration

37
Q

what are the respective directions sensed by the utricle and saccule (otolith organs)

A 
u= horizontal 
s= vertical

(head linear acceleration- translational movements in x,y,z axes)
(together sense linear acceleration and gravity)

38
Q

what senses angular head rotation (around x,y,z axes)

A

semi circular canals

39
Q

what are crista

A

sheets of cells in the semicircular canal where hair cells are clustered

40
Q

what are ampulla

A

bulge along the SCC that contain crista

41
Q

what do the cilia in the SCC project into

A

gelatinous cupula

42
Q

why are all the kinocili in the SCC orientated in the same direction

A

so all excited or inhibited together

43
Q

what are the SCC filled with

A

endolymph

44
Q

what shares a movement plane with the posterior canal of one ear

A

the contralateral anterior canal

45
Q

what happens to the right anterior canal when the left posterior canal is excited

A

is inhibited

46
Q

what happens to the right horizontal canal when the left horizontal canal is inhibited

A

is excited

47
Q

where are hair cells in the otolith organs

A

macula- project from here to the otolithic membrane which has otoconia (calcium carbonate crystals)

48
Q

what is the stiola

A

divides the hair cells of the otolith organs into two populations with opposing polarities (allows otolith to have multidirectional sensitivity- on one side will depolarise exciting afferents, on other will hyperpolarise inhibiting afferents)

49
Q

what in otolith organs will cause a release of glutamate

A

otoconia (calcium carbonate crystals on otolithic membrane) dispacement due to change in tilt of sterocilia

50
Q

what is the central vestibular pathway

A 
vestibular nerve 
vestibular ganglion 
vestibular nuclei 
from here: 
-cerebellum 
-vestibulospinal tract 
-medial longitudinal fasciculus (both ascending and descending components):
-- ascending to abducent, trochlear and oculomotor nuclei

-medial lemniscus (to thalamus and cerebral cortex)

51
Q

what are the three major vestibular reflexes

A

vestibulo- ocular reflex (keeping eyes still when head moves)
vestibulo-colic reflex (head still in space/ on level plane when walking)
vestibular spinal reflex (adjust posture for rapid changes in position)

52
Q

why does alcohol affect the VOR

A

alcohol enters the blood, and then into the cupula. The cupula becomes less dense. It floats in the endolymph more

Neurology (35 decks)

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