active process and Mechanoelectrical Stimulation

AC is a ______ current

transduction

the 2 potentials i nthe absence ofstimulus

(resting potential) Extracellular potential (endocochlear potential) surrounding the stereo cilia Intracellular potential in the OHC / IHC

1 spike represents

1 spike represents = 1 electrical impulse in response to adequate nt release at synaptic cleft

The combination of the intracellular potential and the endocochlear potential results in a ________ according to what theory?

125-160mV cochlear potential, according to the davis battery theory

TEOAE were discovered in

1978 transient evoked called transient bc clicks are quick

explain how the polarity changes from 300 Hz to 5000 Hz

300 = very clear polarity change, time lock or phase locking is clear 5000 = not as clear bc amplitude of A.C. potential decreases as stimulus frequency increases

in AC, phase locking remains its fidelity up to

3000 Hz this means that AC cannot follow the rhythm over 3000 Hz

Consequences of reduced cochlear potential due to diseases reduced the pos potential from 80+ to

40+ mV,

latency of TEOAEs

5-15ms

2 types of gross evoked potentials

AC = cochlear microphonic - 2 polarities DC = summating potential - 1 polarity

whole nerve action potential is made up of

AC and DC

2 types of intracellular measurments

AC= when the current occurs w both pos and neg polarities = alternating current DC = when the pot drives to only one director = direct current

Features of cochlear active process:

Amplification Sharpened frequency selectivity Nonlinear compression OAES

Stimulus-evoked potential (DC) is the

Asymmetry of receptor potential (Intracellular potential)

the IHC deflect away from the mod when the BM...

BM moves towards reticular lamina

steps of IHC depo step 3

Cell partially depolarized (intracellular positively charged) aka the IHC get less neg - this creates a transmembrane current, and this is a receptor responses, not a neural response

stim evoked potentials

Cochlear Microphonic potential (related to extracellular potential) Summating Potential (related to extracellular potential) (Compound) Action potential [(synchronized) activity of auditory nerve fiber(s)]

in DPOAEs how are f1 and f2 related

F2 is higher freq than F1

steps of IHC depo step 2

Force-gated ion channels (tip links) open (K+/Ca++)

what is adaptation

Hair cells responses (transmembrane current) decline over time with a sustained deflection of the stereocilia.

steps of IHC depo, step 5

Influx of Ca++ in IHCs --> fusion of synaptic vesicles /presynaptic membrane--> release of NT (glutamate) to the synaptic cleft --> activation of glutamate receptors (postsynaptic membrane).

stimulus evoked potentials can be

Intracellular potential - (needles into the cell - intracellular) Gross evoked potential - measuring on the surface on the body - we are mirroring the pot of a group of cells (GROSS) not just one

resting endocochlear potential is carried out by which ion

K+ is the main ion carrying out the function High concentration of K+ developed earlier than the positive endocochlear potential

what happens to the magnitude in a dc pot

Magnitude of the receptor potential saturates at a slower rate for the depolarization than for hyperpolarization, pulling the midline towards the depolarization direction

steps of IHC depo step 1

Mechanical deflections of stereocilia (away from the modiolus)

what does negative stiffness generate

OAES

the spectrum of TEOAS

Spectrum narrower than that of the stimulus - Strong in the range of 1-4 kHz, bc of the filter of the middle ear

resting endocochlear potential is maintianed by the

Stria Vasculuris is the source generates and maintains this potential

The travelling wave travels most rapidly over the basal part of the cochlea, and more and more slowly thereafter, therefore

Substantial neural synchrony is needed

who reaserched CM in 1930

The cochlear microphonic (CM): Wever and Bray (1930) placed an electrode on the auditory nerve, connected it to an amplifier in a room 16 meters away and from there to a loudspeaker.

fast adaptation is

Time constant of 0.16- 4 ms after onset of stim(faster as CF increases)

slow adaptation

Time constant of ~20 ms from the base of the OHC efferent system

steps of IHC depo step 4

Voltage-gated Ca++ channels open, further depolarization more pos charged ions are getting into HC, depo = results in more Calcium to get in

what do these lines represent

diffferent lines represent different potential mV to stim tones

as hair bundles move farther away from resting position, it behaves like ______________, but when it's displaced very close to the resting position the hair bundles themselves___________( not how a normal stiffness would behave, this is the neg stiffness)

a regular spring facilities deflection themselves

displacement if BM results in

a relative movement of the tectorial membrane and BM , bc they are hinged separately

stim ekovked OAEs are a result of the

active process

an AC current can be cancelled by

adding response potential invoked by stimulus starting with the opposite phase (polarity)

OAEs are

are sounds generated in the cochlea and recorded in the external ear canal. Source is the active process of cochlea

how is dc a graded pot

as you increase (woo) the stimulus, you will see larger dc potential (larger baseline shift) magnitude of dc potential is reflected as a baseline shift

as the stim level increases, gross action potentials increase bc

at the group level, the action potentials increase = more nerve fibers to respond, which is why we can measure group action potentials however, action potential at the individual cell level isn't graded, its all or none

what is the dc baseline shift

baseline shift is the shift of the midpoint of the pos and neg polarities ac and dc go up together, but the midpoint shift is the dc component DC is distracted from within AC

if glutamate is high enough, that neurofibers will

be activated and generate a pulse -the pulses are the electrical signal made and passed up to the auditory nerve to the cochlear nucleus

the IHC deflect towards the mod when the BM...

bm moves way from tectorial lamina

IHC at rest, step3

cell hyperpolarized (more neg intracellular) no Ca++ gets in, so nothing happens

Pure tone pair evoked (Distortion product—DPOAEs) are used more in

clinic to produce you send int 2 sounds, one high one low, they are related in some wasy F2 is higher than F1 freq relationshio makes these 2 waves overlap

davis battery theory

concept that there are 2 batteries (1 outside and 1 inside the HC) connecting in a serial arrangement and creating a electrical flow (of K+) across OC

Motility of the cell body: Depolarization/hyperpolarization of OHCs triggers

contraction/expansion of the cell body (by up to 4%)— due to the function of prestin (motor protein)

the fluid movement that IHC's are deflected by is created by

created by the deflection of OHC stereocilia.

in DPOAEs, at a freq called the __________, lots of freq are generated, the loudest one comes out as the distortion product of the OAES

cubic freq

how is dc nonlinear

dc potential does not increases as much at higher stim levels as it does as lower stim levels in Fig B as we increase the stim and get larger AC pot, we get more positive ac pot than neg pot w/ 50 nm displacement pos = 4mV, neg = -.6

since phase locking remains until 3000, this means that the amplitude of the AC pot _________ as stim frequency increases

decreases

motility depoalrization

depo = results in contraction, not NT release - drags BM up since it is attached

resting endocochlear potential is inside or outside

extracellular (outside) +80 mV

reduced cochlear potential measn that with a smaller gradnient across the membrane...

fewer ions into the cell body —> NT wouldnt be released

IHC at rest step 2

force gated channels are closed more, less K, less positive charge

when it acts like a normal spring, how are force and distance related

force goes against the direction, and the distance and force grow together

what kind of pot is dc

graded

AC is a ______ potential

graded, its mag changes as the stim level is rasied / lowered - louder = larger AC pot in magnitude

for a non linear system, single tones produe

harmonics

For linear system, its output waveform will contain only

he same frequency components as the input.

the very small passagethat the fluid has to go through is made by the

hensen's stripe proximit to the longest IHC stereo

With a low-frequency stimulus of high intensity that activates fibers of a wide range of characteristic frequencies, it is only the fibers from the___________ that will be activated in synchrony.

high-frequency (basal region)

motility hyperpolarization

hyper = expand - pushes down the BM - made possible by prestin

how do we couunteract reduced pot due to diseases

increase the stim level to defelct more stereocilia bc: you want to open more channels so there are more ions into the cell body the result is an increased threshold

resting intracellular potential

inside IHC -40 / -45 OHC -60 / -70 occurs by extruding positively charged ions (mainly K+, or/and Ca++)

???Single Frequency evoked (SFOAEs) by product of the

instability of the stereo cilia

wha tis happeneing in the DC chart ?

intracellular voltage changes in in IHC for different freq of stim shpw that the relative size of the AC component declines at higher stim freq

OHC motility is a result of

is a result of Mechanical deflections of stereocilia - Force-gated K+ channels (tip links) open/close - Cell partially depolarized / hyperpolarized

the disportion product does wuttt

it travels along the bm to the apical end until it gets to it's characteristic freq site aka the freq of the distortion product is not the same freq of the F1 and F2 interaction, instead it is 2f1-f2, it is closer to the f2 site

nonlinearity was discovered from experiments on

live squirrel monkeys

comprehensive nonlinearity is an explantion for

loudness recruitment - to stop bm from vibrating so loud sounds can be tolerated - they might be more sensitive to loud sounds

AC compressive non-linearity

mag of ac increases as tim increases, but at higher levels, the mag increases isn't as much as the stim level

the action potential is mearsured at the

measured at the cellular level, but the neuron, not hair cell

in an IHC at rest, step 1

mechanical deflections of stereocilia

why is broad tuning bad

more talkers voices get in, more susceptible to noise

when the hair bundles are within a small amount of deflection there is neg/pos force and neg/pos stifness

neg neg

if you increase the stim level ,can you increase the voltage?

no, they all have the same amount voltage therefore, at the cell level the action pot is not a graded pot

how do we find the baseline

pos = 4, neg = -.6, the midpoint is 4 + (-.6) = 3.4 / 2 = 1.7

deflections of stereocilia are proportional to....

proportional to the displacement of BM - the stereo cilia has to move or it will crack bc it gets closer to tectorial membrane, so it bends away from the mod

IHC deflections are proportional to

proportional to the velocity of BM vibration.

in DPOAEs, the traveling waves of 2______ interect on the bm

pure tones

ac Gross potential

record at a distance from the generator cells. = cochlear microphonic bc the result looks just like the stimulus, - the OHCs in basal turn are the main contributors

summating pot

related to extracellualr pit

coch mic

related to extracellualr pot

movement of the BM results in the shearing of the

reticular lamina against the gelatinous tectorial membrane. - this relative movement brings the hair cells closer / farther from the tectorial membrane

a loss in electrical potentials is the loss in

sharp tuning = harder time separating talker from noise and OAEs

dc is the recordings from a

single OHC

AC source

stereocilia

the polarity of an AC currents follows the

stimulus

what is the summating potential

summating is a response from a group of hair cells = a dc potential, so it only goes to one direction - a far field measurement

compound action potential

synchronized activity of audtory nerve fibers

what are TEOAEs used for

teoaes are used for screening, present in Present if 95-99% of individuals w 20 HL hearing or better, only tell us he OHC

what about the channels makes the baseline shift during depo

the channels are already mostly closed at the resting rate, so during hyper, they don't get much more negative bc the channels are closed. Therefore, there is more room for depo and you can get a higher pos

how does this graph show comprehensive nonlinearity

the characteristic freq will have the most flat response -levels lower than the characterstic level will give the same amount of potential than activity as higher levels = 17

however in negative stiffness, the red dashed line, the hair bundle does what

the hair bundle, in the resting position it applies force going to the same direction the displacement goes

freq of distortion product is

the lower freq minus the freq of higher (2xF1 - F2)

is dc compressively non linear

yes

C. what generates froce in this system

the system itself, this is positive feedback

mechanoelectrical Stimulation of Inner Hair cells happens when

they are deflected by a force due to viscous drag from the relative fluid movement in the subtectorial space (turbulance from fluid will deflect stereo cilia)

IHC at rest, step 4

transmembrane current occurs which are receptor responsnes, no release of NT

reading a TEOAEs chart, the bottom tell us what?

wf from teoaes bottom tells us the snr, amp of oae vs background level we are looking at how tall the blue bars are, they are the snr

how does gates opening effect other gates opening

when one gate opens --> each left over channels bears more force and deflects more from its resting position and becomes more likely to open - causes a sequential response

BM response (displacement) is compressively non-linear for tone levels of

~20 to 80 dB SPL)--response grew 0.2 dB per 1 dB increase of tone level