Auditory II

Question 1

Stereocilia contain what?

Answer 1

have nonspecific cation channels called “tip links” connected to shank of neighboring stereocilia

Question 2

Stereocilia resting membrane potentia

what is endocochlear potential

combine to give?

Answer 2

resting Vm = -50 mV

endocochlear = +80 mV btwn endolymph and perilymph

combine to form -130 mV driving force on K+ across stereocilia so K+ wants to move in when NSC open

Question 3

IHC base connect to?
IHC apex connect to?

up and down movement of membrane causes?

Answer 3

base = basilar membrane
apex = tectorial membrane of scala media 

causes beat back and forth

Question 4

inner hair cell response to stereocilia movement procedure

Answer 4

1) sound wave selectively vibrates portion of BM based on tonotopic map (diff prop of membrane)
2) move stereocilia at that part of BM

3) if moves in direction of longest stereocilia, tip links open NSC
OR if move in opp direction, NSC close and hyperpol

4) K+ enter NSC and depol
5) oscillation of membrane potential with freq = sound wave

Question 5

Properties of stereocilia transduction channels

Answer 5

1) NSC
2) voltage insensitive
3) bathed in endolymph (K+ rich)
4) channels connected to shank of neighboring, longer stereocilia by “tip links”

Question 6

role of endocochlear potential in transduction

what happens if no potential diff?

Answer 6

endocochlear potential = +80 mV
endolymph = K+ rich, scala media
perilymph = K+ low, scala vestib and scala tympani

impt for driving force for K+ movement into hair cell and depol

if no driving force, no K+ entry and no depol –> SENSORINEURAL DEAFNESS and CONGENITAL DEAF

Question 7

what is cochlear amplifier

OHCs enhance BM movement in ___ manner for what reason?

Answer 7

mechanical amplif from displacement of BM by outer hair cells

OHCs enhance BM movement in freq dependent manner –> larger and sharper response to pure tones (do-ray-me)

Question 8

efferent innerv from central auditory system on OHCs causes?

OHCs = electromobile so respond to changes in voltage with ___

Answer 8

causes amplify BM movements

responds to changes in voltage with change in length

Question 9

what is prestin

Answer 9

motor protein that causes change in hair cell length since voltage sensitive to sound

Question 10

changes in length of OHC causes what on BM

Answer 10

pulls BM toward or away from tectorial membrane to change mechanical freq selectivity of BM
–> 50 dB of cochlea’s sensitivity to sound

Question 11

what is medial olivocochlear neurons

effect?

Answer 11

efferent neurons that innerv OHCs

sense freq and intensity of sound environment and change cohclear sensitivity

Question 12

MOC neurons are ___ tuned

ex for OHC responding best at 1000 Hz

Answer 12

freq tuned

ex = OHC in BM responding best to 1000 Hz undergoes largest length change when stim with 1000 Hz sound for larger/sharper response to pure tones

Question 13

clinical significance of OHC

example of ototoxic antibiotics

Answer 13

1) susceptibel to damage by ototoxic antibiotics OR prolonged loud sound exposure

antibiotics = streptomycin and gentamycin

2) also susceptible to prolonged exposure to loud sounds

Question 14

how do ototoxic meds cause damage

why are IHC not affected

Answer 14

1) block transduction channel of OHCs
- -> kill them

IHCs not as sensitive

Question 15

what is OAE

how to test

Answer 15

otoacoustic emissions = sounds that active OHCs create b/c they set BM into motion and cause TM to act as loudspeaker

tested using minimicrophones in newborn

Question 16

function of auditory nerve fibers

described by?

Answer 16

fire APs

sound response of single ANF = freq tuning curve

Question 17

rate coding of sound

freq of sound encoded by __
determines __

intensity of sound encoded by

Answer 17

encoded by location of cochlea where afferent fiber innerv an IHC

determines loudness

incr rate of neuron fire AP as sound pressure level incr within freq curve

Question 18

define rate code

what does it mean for ANFs to be tuned?

Answer 18

how peripheral auditory neurons encode sound intensity

tuned or specific freq for which they generate max AP

Question 19

Describe phase locking
importance?

determines ___

Answer 19

for periodic stim (low freq pure tones), ANFs phase lock AP so only fire at either compression or rarefraction for temporal coding

determines PITCH

Question 20

phase locking results from?

Answer 20

neurons tend to fire action potentials only at particular phases (i.e., compression or rarefaction) of the ongoing sound waveform

from the oscillating membrane potential of the
IHCs and the tendency for IHCs to release excitatory neurotransmitter only during the depolarizing phase

Question 21

we use temporal pattern of APs to determine ___

Answer 21

determine pitch of sounds for freq

Question 22

meniere’s triad

Answer 22

1) vertigo with nausea
2) fluctuating low freq hearing loss
3) tinnitus

Question 23

define auditory neuropathy

Answer 23

problem with transmission of info from hair cells to auditory nerve (no phase locking)

patients present with normal near-normal audiogram and otoacoustic emissions but abnormal or absent auditory brainstem responses

have difficulty with speech and temporal processing