["The cochlear amplifier". A crucial component of the hearing mechanism]

The function of the normal hearing organ; as reflected in electrophysiological recordings from the auditory nerve, is characterised by high sensitivity, fine frequency selectivity (tuning), and the presence of non-linearities. These characteristics are already manifest prior to the neural responses, however, and have now been observed in the mechanics of the cochlea in recordings from the organ itself. Cochlear mechanics are linked to the vulnerable 'cochlear amplifier' and the motile capacity of the sensory outer hair cells. Exposure to intense sound or ototoxic drugs may damage the outer hair cells, thus drastically changing both mechanical and electrophysiological responses of the inner ear. The active part played by the outer hair cells is strikingly exemplified by the so-called otoacoustic emissions, the sounds produced by the hearing organ itself even in the absence of external stimuli.