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Mechanical Tuning of Hair Bundles

Through a chain of mechanical processes, sound stimuli cause the deflection of hair bundles of hair cells in the inner ear. This mechanical process, which forms the basis of our sense of hearing, is poorly understood. We have measured the motions of hair bundles in response to sound in an isolated preparation of the cochlea of the alligator lizard Elgaria multicarinata. This image shows cochlear motion at two planes of focus in response to a 4 kHz sound stimulus. The hair cells near the top of the image respond best to tones with frequencies near 4 kHz; those near the bottom respond best to frequencies from 1 to 2 kHz. Our measurements showed that the motion of these hair bundles depends on both the sound frequency and the height of the hair bundle.