Cochlear Electrophysiology

Question 1

Scala media is filled with what kind of liquid? What is the voltage of the liquid?

Answer 1

Endolymph

Positive potential– +80 mV (positive potential is from ATPase ion pump in stria vascularis)

Question 2

Scala vestibuli is filled with what kind of liquid? What is the voltage of the liquid?

Answer 2

Contains perilymph and is near ground potential (0 mV)

Question 3

Scala typmani is filled with what kind of liquid? What is the voltage of the liquid?

Answer 3

Contains perilymph and is near ground potential (0 mV)

Question 4

What is the resting voltage of the outer and inner hair cells?

Answer 4

• 45 = IHC

- 70 mV= OHC

Question 5

Why is it important to have a potential difference across scala media and hair cells?

Answer 5

The stria vascularis produces a +80 mV in endolymphatic space and the inside of the hair cell rests at -70 mV. This 150 mV difference and large voltage gradient drives K+ ions into the hair cell. Because of this difference, ions readily go into the channels and cause depolarization.

Question 6

What is the source of the endocochlear potential? What types of cells help generate it?

Answer 6

The stria vascularis is the source of the endocochlear potential. Intermediate cells have a role in generating this endocochlear potential.

Question 7

Where are the ion channels on the stereocilia?

Answer 7

Location of ion channels thought to be near tips of stereocilia.

Question 8

Stereocilia must be fast enough to do what?

Answer 8

To faithfully reproduce high frequency signal, transduction channels must be fast. (This is helped by side links moving stereocilia in unison)

Question 9

What are the cochlear potentials? Which respond to stimuli?

Answer 9

-Resting potentials (endocochlear potential)

Active potentials
Cochlear microphonic (CM)
Summating potential (SM)
Compound action potential (CAP).

Action potentials occur when there is a change in electrical current due to an acoustic stimulus

Question 10

Which potential mimics the stimulus fine structure? Is it more like AC or DC?

Answer 10

The cochlear microphonic mimic the stimulus fine structure and is more like an alternating current (AC)

Question 11

Which potential mimics the stimulus envelope? Is it more like AC or DC?

Answer 11

The summating potential mimics the stimulus envelope and is more like direct current (DC)

Question 12

Where is the compound action potential generated?

Answer 12

Compound action potential originates in the spiral ganglia and is an onset response from synchronous firing of a group of AN fibers

Question 13

What goes up to higher frequencies, the cochlear microphonic or the inner hair cell potential?

Answer 13

Cochlear microphonic