Abstract
According to the generally accepted theory of mammalian cochlear mechanics, the fluid in the cochlear scalae interacts with the elastic cochlear partition to generate transversely oscillating displacement waves that propagate along the cochlear coil. Using a computational model of cochlear segments, a different type of propagating wave is reported, an elastic propagating wave that is independent of the fluid-structure interaction. The characteristics of the propagating wave observed in the model, such as the wavelength, speed, and phase lag, are similar to those observed in the living cochlea. Three conditions are required for the existence of the elastic propagating wave in the cochlear partition without fluid-interaction: 1), the stiffness gradient of the cochlear partition; 2), the elastic longitudinal coupling; and 3), the Y-shaped structure in the organ of Corti formed by the outer hair cell, the Deiters cell, and the Deiters cell phalangeal process. The elastic propagating waves in the cochlear partition disappeared without the push-pull action provided by the outer hair cell and Deiters cell phalangeal process. The results suggest that the mechanical feedback of outer hair cells, facilitated by the organ of Corti microstructure, can control the tuning and amplification by modulating the cochlear traveling wave.
Highlights
The current theory of mammalian cochlear mechanics has been built upon the observations of cochlear traveling wave first reported by Bekesy [1]
Because the change in the width and the collagen fiber layer thickness of the basilar membrane along the cochlear length is steeper in the basal turn [13,14,17], this slope of mechanical parameters could be underestimated in the basal model and overestimated in the apical model
The asymmetry of the wave envelope: the wave envelope in the apical turn of the cochlea observed by von Bekesy [1] is asymmetrical such that the apical slope is steeper than the basal slope
Summary
The current theory of mammalian cochlear mechanics has been built upon the observations of cochlear traveling wave first reported by Bekesy [1] According to this theory, differential hydrodynamic pressures between the cochlear scalae deflect the elastic cochlear partition to create displacement waves propagating along the length of the partition from the base toward the apex. Observations of the relative motions between OCC microstructures [3,4,5] suggest that the modes of vibration are too complicated for a simplistic mechanical system to explain. These observations led to more detailed OCC models to consider TM
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