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CMSD6310 Audition l > 2.2 Cochlear Physiology ll > Flashcards

2.2 Cochlear Physiology ll Flashcards

1
Q

What is the take-home message of Davis’s battery (below) in your own words as much as possible. (6)

A
  • based on electrical circuits around hair cells in the cochlea
  • two energy pumps that are connected to each other one in the stria vascularis (right side of diagram) and one at the lateral wall of hair cells (left side of diagram)
  • both pumps provide energy for transduction
  • both channels are potassium channels
  • channels are controlled by the bending of hairs
  • channels are MET that have variable resistance and therefore can be adjusted
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2
Q

What is the take-home message of Davis’s battery (below) in your own words as much as possible. (6)

A
  • based on electrical circuits around hair cells in the cochlea
  • two energy pumps that are connected to each other
    -one in the stria vascularis (right side of diagram) and one at the lateral wall of hair cells (left side of diagram)
  • both pumps provide energy for transduction
  • both channels are potassium channels
  • channels are controlled by the bending of hairs
  • channels are mechanical- electrical transduction (MET) - - channels that have variable resistance and therefore can be adjusted
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3
Q

What did electrophysiology experiments teach us about transduction?

A

Transduction occurs at the level of the reticular lamina

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4
Q

What is the tip-link theory (3)

A
  1. Fine filaments called tip links connect the stereocilia to one another.
  2. Mechanical deflection cause hair bundle to tense the tip links and opens ion channels
  3. Transduction channels are located inside stereocilia and are controlled by the bending of the hairs
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5
Q

What did radio-isotopes teach us about transduction?

A

That the transduction channels allow K+ to pass

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6
Q

What kind of channels are involved in transduction?

A

The channels used in transduction are Mechanical-Electrical transduction channels (MET)

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7
Q

How does the MET channel relate to K and other positive ions?

A

The MET current is carried by K however, MET channels are open to all positive ions

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8
Q

Of the two factors that have to do with ion movement , which one drives K mainly?

A

K is mainly driven by voltage via the MET channels because the concentration difference is so small

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9
Q

What are the two reasons for the driving of K?

A
  • There is less disturbance of the intracellular environment due to the high concentration of K inside the HCs
  • K also has a downhill movement which requires no energy and then reduces noise
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10
Q

What is meant by the standing current?

A

A current without sound is a standing current.
(ex: when there is no sound, the MET are PARTIALLY open so there is still current)

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11
Q

Describe the general steps of a standing current. (3)

A
  1. When there is no stimulation, MET channels are open partially, at low level—baseline opening.
  2. K moves from stria vascularis (SV) to SM, into hair cells (through transduction current)
  3. Then K moves out to perilymph (via K channels at the lateral wall of HCs), or supporting cells (via gap-junction) and then back to SV.

One direction in cycle.

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12
Q

Some times, the two voltage and concentration forces are in the opposite direction, the movement of ions is therefore determined by________________

A

the net force

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13
Q

When is there a change to this standing current?

A

Response to sound appears to be a modulation of standing current (either increase or decrease). But the direction of the nerve changes.

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14
Q

What is the voltage and concentration inside the SM?

A

Voltage= +80mV, concentration of K+ 140 mM

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15
Q

What is the voltage and concentration in the hair cells?

A

Voltage= -60mv, concentration of K +137 mM

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16
Q

What is the voltage and concentration in the ST?

A

Voltage= 0, concentration of K 0

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17
Q

What are the three types of links across the stereocilia?

A

1) Row-to-row
2) Side-to-side
3) Tip-to-side

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18
Q

Side-to-side and Row-to-row tip links are ________________________________________________________________

A

thicker and hold stereocilia together

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19
Q

Tip-to-side control ____________________.

A

MET Channels

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20
Q

What are the two possible functions of the links? (2)

A

Connect stereocilia together (the role of side-side, row-row links)
Control of transduction ion channels

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21
Q

What is the most fragile structure of the cochlea to noise?

A
  • Links among the Cilia are most fragile to noise
  • Damage to the links causes the stereocilia disarrangement, reduction of transduction efficacy is expected.
22
Q

Describe the channel opening, tip links, cilia movement and neurotransmitter release in the following situation:

Standing Current

A

Standing Current - ion channel partially open (baseline opening) when quiet.

23
Q

Describe the channel opening, tip links, cilia movement and neurotransmitter release in the following situation:

Depolarization (4)

A

Opening increases,
cilia bend laterally
Tip Links stretched Opening
Inside cells become less negative
Excitation

24
Q

Describe the channel opening, tip links, cilia movement and neurotransmitter release in the following situation:

Hyperpolarization

A

Opening decreases,
Cilia bend medially
Tip links close/compress
Cell even more negative than before
Suppressed

25
Q

Where are the two roles of the Calcium seen?

A

Neurotransmitter release in the hair cells and opening of calcium sensitive K channels at the lateral wall to contribute to repolarization.

26
Q

Describe the overall 8 steps of transduction:

A

k influx from MET channel
depolarization
Ca influx
repolarization
hyperpolarization
repolarization
repeat

27
Q

The lateral bending of OHC (depolarization) cause their size to_____________

A

shorten

28
Q

What protein has a role in the shape change for OHC?

A

Prestine

29
Q

What is transmission?

A

The electrical biochemical release of a neurotransmitter to create an action potential in the spiral ganglion neuron.

30
Q

What is a spontaneous action potential (as it relates to transduction in this case)?

A

Spontaneous action potentials are the baseline release of a neurotransmitter to result in an action potential.

31
Q

What increases the chance of Aps?

A

Stereocilia being bent laterally.

32
Q

Based on the three steps of signal processing in the cochlea, please respond: Conduction involves ____________________________________________________________________________________________

A

Conduction involves the change in signal processing from: mechanical to hydrolic mechanical -> macro -> micromechanics

33
Q

Based on the three steps of signal processing in the cochlea, please respond: Transduction involves ____________________________________________________________________________________________

A

Transduction involves the change in the signal processing from: mechanical to electrical

34
Q

Based on the three steps of signal processing in the cochlea, please respond: Transmission involves ____________________________________________________________________________________________

A

Transmission involves the change in the signal processing from: Electrical (receptor potential)-biochemical (neurotransmitter release) to action potential of SGN

35
Q

What can the role of the OHC be summarized as?

A

MECHANICAL AMPLIFIER - INTERNAL HEARING AID

36
Q

What are two traits of the healthy cochlea that was not identified by Bekesy?

A

Lower threshold (the lowest sound level to evoke response better frequency selectivity

37
Q

What are the two sensitivities affected by the active mechanism of hearing?

A

sensitivity to sound & frequency selectivity

38
Q

What is the role of the OHC in Frequency selectivity?

A

OHC amplify soft sound so the cochlea can perceive, and OHC increases frequency selectivity

39
Q

What are the three main evidences that show the OHC role in amplification?

A

Motility of OHCs
Lesion studies—OHC lesion poor tuning and poor sensitivity
Otoacoustic Emissions: ear can produce sound, this shows OHC function: generating mechanical force

40
Q

Describe the the fast Motility of OHC:

A

Fast body motility responds to voltage change - in vitro studies

41
Q

Describe the negative impacts of lesions on OHC:

A

Lesions on OHC indicates poor tuning and poor sensitivity

42
Q

Describe the relationship between Otoacoustic emission and OHC:

A

ear can produce sound, this shows OHC function: generating mechanical force

43
Q

What are the two types of OHC motility? Which type is seen in amphibians and not mammals?

A

hair bumble motility in amphibians and fast OHC motility in mammals

44
Q

How fast is the fast OHC body motility? What is it proportional to?

A

flows up to 20Hz and is proportional to membrane potential changes

45
Q

How much does the length change?

A

the length changes up to 5%, 1-5um

46
Q

What protein is responsible for the change in the shape of the outer hair cell?

A

prestin

47
Q

What are the stages of signal processing in the OHC shape change?

A

The signal is from mechanical to electrical and then mechanical.

48
Q

What are the stages of signal processing in the OHC shape change?

A

The signal is from mechanical to electrical and then mechanical.

49
Q

The cochlea is more sensitive to sound than the
vestibular apparatus because:

A

The special accessory structures effectively
convert the sound to stimulate hair cells in
cochlea than in the vestibuli.

50
Q

Compared to inner hair cells, outer hair
cells are:

A
51
Q

Which cell type provides support to
OHCs?

A

Dieter’s cells

52
Q

Electrical polarization means that there is:

A

a voltage difference between extra and intra cellular spaces.

CMSD6310 Audition l (16 decks)

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