cochlear physiology

Question 1

what is the function of the cochlea?

Answer 1

The function of the cochlea is to act as an interface between the physical world of sound and the brain.

Question 2

what is the cochlea?

Answer 2

The cochlea is a fluid-filled structure that contains the sensory organ of hearing called the organ of Corti.

Question 3

the organ of corti translates what to what?

Answer 3

translate vibrations into electrical impulses

Question 4

once electrical impulses are done, what are the turned into

Answer 4

Electrical impulses are then carried to the brain by sensory nerves where they can be decoded and perceived as sound

Question 5

hair cells turn what into what?

Answer 5

Hair cells in the cochlea turn mechanical energy of sound waves into a change in membrane potential –this allows the cell to signal the VIIIth Nerve

Question 6

OHC amplify what?

Answer 6

Outer hair cells (OHCs) amplify movement of the basilar membrane during low-intensity sound stimuli

Question 7

what allows the OHC length to be changed ?

Answer 7

-Motors allow for this by being able to change the length of OHC
-Change in membrane potential drives the motor
-They’r called motor b/c it can change the positional relationship of membranes around OHC

Question 8

what else are ohcs?

Answer 8

its an active mechanism
why? because Outer hair cells sharpen the tonotopic organization established by the mechanical properties of the basilar membrane

Question 9

what is the bottom line around OHC?

Answer 9

The mechanical properties of the basilar membrane cannot account for the precise place-coding of frequency in the auditory system. Another, active, mechanism sharpens the mechanical response of the basilar membrane.

Question 10

what are characteristics of cochlear amplification ?

Answer 10

-Motors allow for an amplification in the
basilar membrane
-Greater change in length allows for stereocilia
to bend more
-Leads to more transduction
-Greater response
-This mechanical amplification allows for a 100 fold greater hearing sensitivity (40dB)

Question 11

t/f is there a relationship between the OHC’s electromotility and the action of the being a cochlear amplifier ?

Answer 11

true and this results in OAE

Question 12

what initiates electrochemical changes within the OHC

Answer 12

Deflection of the hair bundle (stereocilia by the classic macromechanical traveling wave of von Bekesy, and the resulting opening of the stereocilia’s ion channels initiates electrochemical changes within the OHC.

Question 13

what is the result of the intracellular voltage change?

Answer 13

The resulting intracellular-voltage change induces repetitive shortenings (depolarization) and elongations (hyperpolarization) of the OHC that follow the stimulus frequency cycle-by-cycle.

Question 14

because of the intracellular voltage change, what happens after?

Answer 14

This OHC electromotility acts to enhance the region of maximal displacement of the incoming stimulus’s mechanical traveling wave by enhancing its amplitude and sharpening its peak.

Question 15

what is “ the actions of the cochlear amplifier?

Answer 15

Together, the OHC electromotility process and its consequences on the region of maximal activation in the organ of Corti are referred to as the actions of the cochlea amplifier.

Question 16

are the OHC linear or nonlinear?

Answer 16

he OHC response does not increase linearly with increasing intensity. It “levels off” at high intensities. Its response is nonlinear

Question 17

what is the consequence of the nonlinearity of the OHC?

Answer 17

distortion

Question 18

what are facts we know about efferent fibers?

Answer 18

-Don’t need them to get outer hair cell motility/ cochlear amplifier
-May modify motility or cochlear amplifier.
-Reduction in masking
-Selective attention
-Protection from intense sound
-Adjust input to two ears to maintain balance

Question 19

what are the main idea around OHC?

Answer 19

1)Outer hair cells function to sharpen the displacement pattern of the basilar membrane.
2)OHCs also improve sensitivity to sound – they make response thresholds lower. They “amplify”

Question 20

what does motility mean?

Answer 20

1)Motility is the likely means by which OHCs accomplish these functions.
2)It is not entirely clear why the efferent innervation of the OHCs affects cochlear responses.

Question 21

what is something important to remember in regards of the traveling wave?

Answer 21

It is important to remember that auditory nerve fibers are not themselves frequency specific at all, but depend on the inner hair cells to select their input.

Question 22

what is the first function benefit of the traveling wave

Answer 22

Distribution of sound stimulus energy across cells by frequency relieves individual auditory nerve fibers of having to convey the individual cycles of vibration of the original sound – which they do badly above 500Hz.

Nearly all of the useful information available in a narrow band of frequencies is carried by fluctuations in the amplitude of the waveform.

Question 23

what is the second function benefit of the traveling wave

Answer 23

The sharper the focus on the organ of Corti, the stronger the peak of excitation achieved for each single frequency, resulting in enhanced detection sensitivity.

the sharper the focus, the more strongly is interfering information at other frequencies rejected, resulting in greater noise immunity – greater frequency selectivity.

Question 24

what is the third function benefit of the traveling wave

Answer 24

The sharper the focus, the narrower is the bandwidth of frequencies presented to each hair cell, resulting in a reduction in the rate of information flow through each inner hair cell and nerve fiber.