Making an effort to listen: mechanical amplification by myosin molecules and ion channels in hair cells of the inner ear

A.J. Hudspeth
Laboratory of Sensory Neuroscience, Rockefeller University

(March 28, 2011 2:30 PM - 3:30 PM)

Making an effort to listen: mechanical amplification by myosin molecules and ion channels in hair cells of the inner ear

Abstract

In addition to responding to mechanical stimuli, the hair cell's transduction apparatus mediates active hair-bundle motility, one mechanism underlying the active process that increases responsiveness to sound, sharpens frequency selectivity, compresses the dynamic range of hearing, and even causes spontaneous otoacoustic emissions. In non-mammalian tetrapods-and perhaps in mammals as well-mechanical amplification is accomplished by active hair-bundle motility, which results from the interaction of negative hair-bundle stiffness with the myosin 1c motors that underlie adaptation. The operation of the active process near a Hopf bifurcation explains many of the characteristics of hearing. In particular, the dependence of response amplitude on stimulus force is expected to follow a power law with an exponent of one-third, as is measured experimentally. Operation near a Hopf bifurcation additionally produces distortion products with the level dependence observed for human hearing. Finally, a critical oscillator can become unstable, providing a natural explanation for spontaneous otoacoustic emissions.