Wada H.

The ears are paired sense organs, which collect, transmit, and detect acoustic impulses. Each of them is comprised of three main parts: the outer ear, middle ear, and inner ear. Traveling sound is focused into the external auditory canal by the pinna, causing vibration of the tympanic membrane and motion of the three ossicles in the middle ear. Their motion is transmitted to the cochlea of the inner ear. The mechanical motion of the basilar membrane in the organ of Corti is then transduced into encoded nerve signals in the cochlea, which are transmitted to the brain. Even though the amplitude of tympanic membrane vibrations is only a few nanometers when we speak in a low voice, we can clearly understand what is being said. This is due to cochlear amplification caused by the motility of outer hair cells (OHCs), which are located in the organ of Corti of the cochlea. The origin of this motility is believed to be associated with a membrane protein in the lateral wall of OHCs. The gene that codes for this protein has been identified and termed 'prestin.' Prestin has been found to be a direct voltage-to-force converter, which can operate at microsecond rates. In my talk, firstly, actual measurement results of the tympanic membrane vibrations will be shown by video. Secondly, a dynamic animation of how the middle ear and cochlea function will be presented. Thirdly, the motility of the isolated OHC will be demonstrated, and the function of the OHCs, which behave like actuators of mechanical structures, will be discussed. Finally, images of prestin obtained by an atomic force microscope will be displayed.