ASA 127th Meeting M.I.T. 1994 June 6-10

2pPP3. H. Davis's concepts of cochlear mechanics in evolution.

Jozef J. Zwislocki

Inst. for Sensory Res., Syracuse Univ., Syracuse, NY 13244-5290

Two concepts are considered. One refers to the cochlear amplifier, the other, to hair cell stimulation. According to the first, a biological amplifier produces strong amplification at the falling edge of the passive wave envelope and produces a sharp amplitude peak there. When the amplifier is eliminated, only a less sharp passive peak remains at a more basal location. It has been demonstrated experimentally that, at a given cochlear location, when the amplifier is eliminated, the sound frequency of the amplitude peak is lowered by about an octave. This is equivalent to a basal shift of the maximum by over 2 mm. According to the second concept, cochlear hair cells are depolarized by deflection of their stereocilia toward the spiral ligament. The deflection is due to shear displacement between the reticular lamina and the tectorial membrane, which is supposed to take place during basilar membrane displacement toward scala vestibuli as a result of the geometry of the organ of Corti. Experiments show that this is often not true. The discrepancies can be explained on the basis of experimental evidence concerning the dynamics of the stereocilia and the tectorial membrane. [Work supported by NIDCD.]