Effect of the cochlear microphonic on the limiting frequency of the mammalian ear.

Electromotility is a basis for cochlear amplifier, which controls the sensitivity of the mammalian ear and contributes to its frequency selectivity. Because it is driven by the receptor potential, its frequency characteristics are determined by the low-pass RC filter intrinsic to the cell, which has a corner frequency about 1/10th of the operating frequency. This filter significantly decreases the efficiency of electromotility as an amplifier. The present paper examines a proposal that the cochlear microphonic, the voltage drop across the extracellular medium by the receptor current, contributes to overcome this problem. It is found that this effect can improve frequency dependence. However, this effect alone is too small to enhance the effectiveness of electromotility beyond 10 kHz in the mammalian ear.