Input–output characteristics of the tectorial membrane in the frog basilar papilla

The basilar papilla (BP) in the frog inner ear is a relatively simple auditory receptor. Its hair cells are embedded in a stiff support structure, with the stereovilli connecting to a flexible tectorial membrane (TM). Acoustic energy passing the papilla presumably causes displacement of the TM, which in turn deflects the stereovilli and stimulates the hair cells. In this paper we present optical measurements of the mechanical response of the TM to various stimulus levels. Results were obtained from 3 specimens (4 ears). The phase of the displaced area of the TM was constant across stimulus levels. Phase differences between the orthogonal spatial motion components were either close to 0° or 180°. These findings were consistent with a TM motion along the epithelium surface. The TM response was linear for stimulus levels up to −30 dB (re. 1 μm) at the operculum. This amplitude was estimated to exceed that at which neural responses saturate. Apparently, saturation of the neural response in the frog inner ear is not based on saturation of the mechanical response of the tectorial membrane.