Hair Cells and Neural Impulses

Resonance Theory

*Outdated

Basilar membrane behaves like a series of independent resonators

Each part of the BM resonates to a specific frequency

Bekesy’s Traveling Wave Theory

Shows a wave like motion along the membrane, with peak displacement depending on frequency

Intensity Coding for soft sounds

OHC amplify sound signals via electromotility (using Prestin)

Intensity coding for loud sounds

IHC respond directly

OHC not needed for amplification

Broader and larger BM displacement = more neural firing

Otoacoustic Emissions

Sounds generated by the cochlea (from OHCs)

Receptor Potentials

AC: Dominate at low frequencies

DC: Dominate at high frequencies

Spontaneous Firing

Nerve fibers fire in absence of sound stimulation

Increases with intensity

Spontaneous Rate

Number of spikes per second in absence of input sound

Low Spontaneous Rate

Responds to loud stimulus

High Spontaneous Rate

Responds to soft stimulus

Place Coding

Different frequencies activate different locations of the BM —> Preserved in auditory nerve

Works across all frequencies

Phase Locking

Neurons fire at specific phases of low frequency sounds (< 5 kHz)

Better for low frequencies

Volley Theory

Multiple neurons take turns to encode high frequency noises