Seminar: Biophysics of the inner ear

Most sounds of interest consist of complex, time-dependent admixtures of tones of diverse frequencies and variable amplitudes. To detect and process these signals, the ear employs a highly nonlinear, adaptive, real-time spectral analyzer: the inner ear, or cochlea. Sound evokes a wave on the cochlear basilar membrane, an elastic band spiraling along the cochlea between two fluid-filled chambers. The oscillations of the basilar membrane deflect hair bundles, the mechanically sensitive organelles of the ear's sensory receptors, the hair cells. In addition to transducing mechanical inputs, hair cells amplify them by an active process. The active process can in turn be regulated through efferent feedback from the auditory cortex. I present recent theoretical and experimental work on how this active process works in the low-frequency region of the cochlea, which is responsible for detecting the low frequencies that are most relevant for speech. In particular, I present data from laser-interferometric experiments and mathematical modelling that show that the apical organ of Cort can function as an elctromechanical transistor.