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Neural circuits > Lecture 6 - overview of auditory system > Flashcards

Lecture 6 - overview of auditory system Flashcards

1
Q

what is sound frequency?

A
  • number of cycles per second
  • frequencies from 20Hz-20kHz
  • achieved by mechanics if cochlea and physiology of hair cells
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2
Q

what is sound intensity?

A
  • amplitude of wave from peak to peak
  • achieved by firing rate of many nerve fibres
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3
Q

onset

A

rapid onset is important for localising different sounds and creating a map of auditory world around us

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4
Q

duration

A
  • ear remains sensitive to sounds for long periods without fatigue
  • never rests and is always on
  • all info is encoded by hair cells and nerve fibres
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5
Q

travelling of sound wave

A

sound wave travels down outer ear to tympanic membrane and through the cochlea

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6
Q

what is the cochlea innervated by?

A

auditory nerve

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7
Q

three compartments of the cochlea

A

scala vestibuli, scala media and scala tympani

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8
Q

where does organ of corti sit?

A

on the basilar membrane

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9
Q

what does scala vestibuli and scala tympani contain

A

perilymph (normal extracellular solution) resting potential of +80mV

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10
Q

endocochlear potential

A

+80mV

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11
Q

what does scala media contain?

A

endolymph which has a very high potassium concentration compared to normal

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12
Q

where are high potassium created?

A

by cells in the stria vascularis and pump potassium in scala media

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13
Q

resting potential of sensory hair cells

A

-60mV

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14
Q

the result of the different potentials of the two solutions (endolymph and perilymph)

A

makes a high driving force and is vital for how they function (140mV)

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15
Q

perilymph contents (normal)

A
  • low potassium
  • normal calcium
  • high sodium
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16
Q

endolymph contents

A
  • high potassium
  • low calcium
  • low sodium
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17
Q

hair cells in organ of corti

A
  • inner hair cells are main sensory cells and encode all auditory information for brain
  • outer hair cells do not have sensory role but are important for cochlea amplification
18
Q

tonotopic organisation of mammalian cochlea

A

cells of the base are activated by high frequency sounds and cells at the apex respond to low frequency sounds

19
Q

place-frequency code

A

the position of the active inner hair cell along the cochlea that encodes the sound frequency

20
Q

what is cochlea tonotopicity established by?

A

the basilar membrane travelling wave. wave travels along the basilar membrane that travels from base to apex

21
Q

characteristic frequency

A

sound of one frequency causes maximal movement of the basilar membrane at one location

22
Q

lower frequency sound on basilar membrane

A
  • travels further along basilar membrane
  • causes maximal movement towards apex
  • characteristic frequency location is closer to apex
23
Q

higher frequency sound on basilar membrane

A
  • travels less along the basilar membrane
  • causes maximal movement towards the base
  • characteristic frequency location to the base
24
Q

what is the characteristic location determined by?

A

width and stiffness of basilar membrane
- apex is wide and floppy’
- base is narrow and stiff

25
Q

inner hair cells

A
  • primary sensory receptors
  • encode all auditory information and pass it onto nerve fibres
26
Q

what are inner hair cells defined by?

A

the stereocilia hair bundle

27
Q

what are within the stereocilia

A

mechanosensitive ion channels - called mechanoelectrical transducer channels (MET)
- these channels join the taller stereocilia next to it

28
Q

inner hair cells at rest

A
  • slight tension on tip links and transducer channels open creating a transducer current
  • resting inwards MET current is -55mV
  • potassium ions enter down large electrical gradient (140mV)
  • potassium ions enter perilymph at bottom of cell
29
Q

what keeps the perilymph and endolymph separate?

A

a tight barrier

30
Q

inner hair cells in the two solutions

A

hair bundle is in endolymph and cell body is surrounded by perilymph

31
Q

inner hair cells with excitatory stimulation

A
  • large deflection of hair bundle towards the taller stereocilia. increases tension in tip links
  • opens MET channels and causes large MET current
  • depolarises hair cell (-30mV) and activates the calcium channels
  • ## inner hair cells do not fire action potentials, they respond to motion
32
Q

depolarisation of inner hair cells potassium channels

A

activates potassium channels
- potassium ions exit down concentration gradient into perilymph to help repolarise cell

33
Q

inner hair cells with inhibitory stimulation

A
  • large deflection of hair bundles towards shorter stereocilia and making tip links slack
  • closes MET channels and turns off MET current
  • hyperpolarises hair cell below resting potential
  • potassium channels open for longer to repolarise cell (-65mV)
34
Q

Inner hair cells with sustained stimulation

A
  • sustained sound moves hair bundle back and forth at sound frequency
    creates a cycle of membrane potential matching sound frequency and hair cell moves back and forth
  • generates pulses of neurotransmitter release and afferent activity
  • sensory information relayed to brain
35
Q

outer hair cells

A
  • function as the cochlear amplifier
  • they shorten and lengthen in time with sound - electromotility
  • they do not have many afferents
36
Q

function of Prestin

A
  • in the outer hair cell membrane
  • allows the hair cell to shorten or elongate in response to changes in membrane potential
37
Q

outer hair cell stimulation

A
  • outer hair cells stimulation works the same for inner hair cells
  • at rest there is a resting MET current
38
Q

outer hair cell resting potential

A

around 40mV

39
Q

what causes outer hair cells to shorten

A

when they depolarise

40
Q

the combined movement of 3 rows of outer hair cells

A
  • acts as a positive feedback in cochlea
  • increases movement of basilar membrane
  • increases stimulation of inner hair cell bundles
  • outer hair cells amplify the stimulation of inner hair cells
41
Q

how outer hair cells affect movement of basilar membrane

A
  • outer hair cells electromotiltiy amplifies basilar membrane motion
  • basilar membrane movement is greatly increased with cochlear amplification
  • results in sharply tuned and highly sensitive inner hair cells
42
Q

loss/ damage of outer hair cells

A
  • stimulation of inner hair bundle is weaker
  • severe hearing loss but not complete deafness
    still have basic tuning of basilar membrane

Neural circuits (11 decks)

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