Cochlear Physiology

Exam 3

what make up sound waves

condensations and rarefactions

condensations

high pressure

rarefactions

lower pressure

traveling wave

pressure wave that travels from OW through cochlea

during condensation the BM is driven __

downwardsd

during rarefaction the BM is driven __

upwards

what does this up and down displacement create

transverse displacement

the frequency of a stimulus is represented by what

location of maximum displacement

basal end of BM

thick and narrow = stiff

fast movements

best for high frequencies

apical end of BM

thin and wide = less stiff

slow movement

best for low frequencies

what happens after resonance point is reached

traveling waves dies quickly after

upward spread of masking

this is when low frequency masks high frequency 

if you amplify low frequencies in HA, the background noise will be too loud

high frequency travels __, low frequency travels __

less, more

what represents intensity

amount of BM deflection

if you increase intensity what happens to BM

peak displacement causes amplitude to grow and broaden

displacement of the BM is

nonlinearw

why is displacement of BM nonlinear?

protection mechanism for organ of corti

what happens if BM displacement is linear?

too much movement too fast can cause damage

how is cochlea organized?

tonotopically

what does tonotopic organization mean?

base - high frequencies

apex - low frequencies

what is a healthy cochlea

highly frequency selective

what inputs are more frequency specific

soft sounds

is talking louder if someone doesn’t hear you effective?

no, more intensity does not mean better

how does the tectorial membrane move compared to BM

perpendicular, in a radial movement (side/side)

what is shearing force

when the tectorial membrane moves in radial movements, perpendicular to the BM movement

upward movement of BM is known as

rarefaction

what happens upward movement of BM

cilia bend to tallest one (outward)

depolarization

excitation

downward movement of BM known as

condensation

what happens in the downward movement of BM

cilia bend to the shortest (inward)

hyperpolarization

inhibition

what is MET

mechano-electrical transduction

normal state of hair cells

polarized (inside more negative than outside)

what happens in MET

BM moves up, cilia move to tallest, tip-links stretch and pores open

what happens when pores open

depolarization, positive K+ ions from endolymph enter the hair cell body

what is depolarization

making the inside of a cell slightly less negative

process of depolarization

cilia bend to tallest, pores open, excitation, IHC release neurostransmitter, OHC contrat

process of polarization

cilia bend to shortest, pores close, inhibition, IHC decrease firing of auditory nerve, OHCs expand

resting potentials

potentials you can record with no stimulation

endocochlear and intra-cellular potential

endocochlear potential

direct current (steady)

located in endolymph of SM - greatest potential is in stria vascularis where endolymph is made

positive potential = 80 mV

intra-cellular potential

direct current (steady)

IHCs: -40 mV

OHCs: -70 mV

sound evoked potentials

cochlear microphonic, summating potential, compound action potential

cochlear microphonic (catches sound)

alternating current (up/down movement)

generated by OHCs

occur during sound presentation

reflects intensity and frequency components of sound

summating potential

direct current (steady)

sum of potential hair cells

generated by IHCs

when a sound is presented, it causes shift in baseline potential

compound action potential

short alternating current signal

generated by spiral ganglion neurons

sum of action potentials of multiple auditory neurons firing at the same time

what is electrocohleography

test to measure different cochlear potentials

role of inner hair cells

act as auditory biological transducersw

sequence of events for IHCs

shearing force → pores open → K+ flows in → depolarization → IHCs release glutamate (neurotransmitter) → hits nerve fibers to signal brain

if tectorial membrane is not touching the stereocilia of IHCs, how do the move?

the movement of fluid causes IHCs to move

what is the role of the OHCs

electromotility

what is the protein in OHCs and what does it do

prestin, changes the length of OHCs in response to change in charge

what does depolarization cause the OHCs to do

contract

what does hyperpolarization cause the OHCs to do

expand

OHCs have a high sensitivity to

weak sounds/low intensity

what is the cochlear amplifier

sharp frequency tuning, not active at high intensities = nonlinearity

tuning curve

find what frequency and intensity a single hair cell responds best at

what do OAEs measure

how well OHCs are functioning

can OHCs grow back

no, once damaged they are gone

OHC damage

mild to moderate HL

OHC and IHC damage

severe HL

what sounds to OHCs amplify

soft sounds

auditory transduction summary

1. sound vibration

2. outer ear: pinna and EAC funnel/collect

3. middle ear: impedance match and push to cochlea

4. inner ear: transverse movement of BM causes shearing motion of tectorial membrane

5. inner ear: displacement of stereocilia opens MET channels, changing electrical charge across hair cell

OHC role run through:

BM moves up

stereocilia moves (to tallest/shortest)

pores (open/close)

endolymph (+/-) comes in

depolarize cell

cell excites

OHC (expand/contract)

BM moves up

stereocilia moves (to tallest)

pores (open)

endolymph (+) comes in

depolarize cell

cell excites

OHC (contract)