displacement of hair bundle to taller SC inc. # of open channels, producing an increase of inward resting current deploarizing voltage change = receptor potential inc. permeability to (+) dep more NTs released
at high tone bursts, rate decreases b/c fiber is adapted and less likely to respond
How can the auditory nerve signal the large range in level of audible sound from 0-100 dB? (b/c when theres masking fiber can’t signal changes in tone burst)
1.) as the level of tone increases more and more fibers that are tuned to other CF begin to respond, b/c tuning ccurves become broader at higher sound levels
2.) auditory nerve fibers vary in sensitivity to sound and as sound level is incresaed, the less sensitive fibers begin to respond
Phase-Locking: when neurons only fire at a preferred phase of the sound wave at each cycle, usually at peak amplitude
- phase-locking in nerve fibers results from the phasic release of NT as dictated by the ac receptor potential
- @ low frequencies, neurons can fire APs at every cycle, easy to determine frequency of sound b/c it’s the same as the frequency of the neurons APs
- @ higher frequencies (1kHz-4kHz), neurons can’t fire AP w/ every cycle, b/c firing rate is limited by refractory periods
- the only code for sound frequency at high frequencies is the place code
- intensity of stimulus is encoded by the # of fibers that are active other than frequency of firing
The relationship between degree of bundle deflection and receptor potential magnitude is neither linear nor symmetric
I.E. – displacement of bundles in the depolarizing direction produces larger response than equal displacements in the other direction = sigmoidal input and output (not sine)
Thus, symmetrical sinusoidal deflections of the bundle (as might occur with acoustic stimuli) will produce both (ac) and (dc) changes in membrane potential.
dc Component = superimposed depolarizing steady-state
ac Component = sinusoidal
- as you increase F, there is less of this but dc component will remain unperturbed (this is called rectification)
OHC: function to amplify the signal so there is a high sensitivity to hearing
- decrease in resting length by a factor of 4 from the apical to the basal ends, responds by altering its length
- there is a driving force to hyper- and de-polarize the cell depending on K+ and Ca2+ channels
- depends on ratios of ion channels and capacitance of the membrane, there are also big and small hair cells, EX: bigger hair cells respond better to lower F
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