The cochlear amplifier: augmentation of the traveling wave within the inner ear.

PURPOSE OF REVIEW: There have been many recent advancements in our understanding of cochlear function within the past ten years. In particular, several mechanisms that underlie the sensitivity and sharpness of mammalian tuning have been discovered. This review focuses on these issues.

RECENT FINDINGS: The cochlear amplifier is essentially a positive feedback loop within the cochlea that amplifies the traveling wave. Thus, vibrations within the organ of Corti are sensed and then force is generated in synchrony to increase the vibrations. Mechanisms that generate force within the cochlea include outer hair cell electromotility and stereociliary active bundle movements. These processes can be modulated by the intracellular ionic composition, the lipid constituents of the outer hair cell plasma membrane, and the structure of the outer hair cell cytoskeleton.

SUMMARY: A thorough understanding of the cochlear amplifier has tremendous implications to improve human hearing. Sensorineural hearing loss is a common clinical problem and a common site of initial pathology is the outer hair cell. Loss of outer hair cells causes loss of the cochlear amplifier, resulting in progressive sensorineural hearing loss.