Longitudinal pattern of basilar membrane vibration in the sensitive cochlea Tianying Ren Proceedings of the National Academy of Sciences, USA, early edition,
Dec 2, 2002 (pnas.262663699) Oregon Hearing Research Center (NRC 04), Department of Otolaryngology
and Head and Neck Surgery, Oregon Health and Science University, 3181
Southwest Sam Jackson Park Road, Portland, OR 97239-3098, USA Abstract: In the normal mammalian ear, sound vibrates the eardrum, causing the
tiny bones of the middle ear to vibrate, transferring the vibration to
the inner ear fluids. The vibration propagates from the base of the cochlea
to its apex along the cochlear partition. As Comment: The vibration of the mammalian cochlear partition has now for the first time been measured with a scanning laser. Tianying Ren recorded basilar membrane (BM) motion of an uninterrupted longitudinal section of 900 µm in the gerbil cochlea. He collected data for the complete range in a single recording using a scanning laser that automatically operated in steps of 2.5 µm. Major results were (1) that up to about 50 dB SPL the longitudinal range of BM excitation is symmetrical around CF, and (2) that at 10 dB SPL the total longitudinal range of BM excitation is ca. 600 µm, that is 300 µm on either side of the given point of characteristic frequency (CF). These results agree with earlier ones reported by Russell and Nilsen (1997, PNAS 94, 2660-2664) and Nilsen and Russell (2000, PNAS 97, 11751-11758). They indicate that at low sound levels BM motion reflects a local resonance in the organ of Corti, probably originating from intrinsically tuned, motile outer hair cells (OHC). Ren's new technique has large potentials for future explorations. The speed of the BM traveling wave (TW) as a function of longitudinal location can now be determined with high precision at many different sound levels. Thus it will be possible to obtain a detailed analysis of both the passive and the active, OHC-driven, components of the TW, which is necessary for an understanding of cochlear function. (Comment Martin Braun) |