Micromechanical Basis of High-Frequency Tuning in the Bobtail Lizard

Abstract

To date, a good understanding of the mechanisms of frequency selectivity has been achieved for the auditory papillae of the red-eared turtle (Crawford and Fettiplace, 1981), the alligator lizard (Weiss and Leong, 1985) and mammals (Khanna and Leonard, 1982; Russell and Sellick, 1978; Sellick et al., 1982). However, none of the three types of models proposed are directly applicable to the other cases. In the red-eared turtle, tuning seems to be mainly a function of the electrical properties of individual hair cells, whereas in the alligator lizard at least the high-frequency hair cells seem to be tuned by the resonance properties of individual hair-cell stereovillar bundles. Mammalian hair cells, however, show no indication of being electrically tuned and are covered by a thick tectorial membrane which, at least for outer hair cells, does not allow individual hair cell bundles to resonate independently. The mechanisms of frequency selectivity in vertebrate inner ears are obviously quite diverse (Manley, 1986), so that a comprehensive and comparative understanding of tuning mechanisms and their integration in the hearing organs of different vertebrate classes requires the detailed investigation of a greater variety of morphological types of inner ear.