Responses of the salamander inner ear to vibrations of the middle ear

Abstract

Microphonic and action potentials were recorded from the inner ear and eighth cranial nerve respectively of Notophthalmus viridescens, supine in air, while the exposed operculum of the middle ear was vibrated. Microphonic potentials were double the frequency of the vibrating source and were produced for a range of vibrations from 30 to at least 700 Hz. Sensitivity functions were irregular. Action potentials were obtained for a range of vibrations from between 30 and 60 Hz up to 550 Hz depending on the recording site. Populations of neurons were found that were narrowly tuned to a range of frequencies and that had peak sensitivities representing almost the entire range of frequencies to which responses were obtained (50–400 Hz). The most sensitive preparation required only 0.003 μm (peak to peak) with a peak sensitivity at 400 Hz to obtain a response. Vibration energy applied to a part of the middle ear can activate inner ear sense organs and at least part of this information can reach the central nervous system.