MECHANICS OF THE ORGAN OF CORTI

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The objective is to understand the role of the mechanical (fluid-elastic-visco-elastic) activity in the transformation of sound into receptor cell stimulation. This will be a continuation of mathematical studies involving appropriate adoptation of asymptotic techniques of wave analysis. Fundamental to this work is the use of only physiological parameters in the mathematical models. Recent results are (1) frequency localization along the cochlea can be explained in terms of only the width, thickness and fiber density of the basilar membrane pectinate zone (PMP); (2) the response of BMP is little affected by cochlear curvature, opening and partial draining of one scala, and by details of the organ of Corti stiffness; (3) a tuned cochlear resonator, found in the horseshoe bat, causes a sharp drop, rather than a peak, in BM amplitude at the frequency of tuning; and (4) DC streaming must be an important feature of cochlear function. The bat cochlea results indicate that much of the current thought is incorrect. Specific accomplishments in the proposed work are to include: (1) Extension of the "large finite element" approach from 2-D to 3-D cochlear models. This is an approach which combines the computational efficiency of the 'WKB' method with the capability of direct numerical methods for handling discontinuities. Specifically, the details of the horseshoe bat partition response will be determined. (2) Development of a realistic uncoupled micromechanical model of the organ of Corti and sulcus fluid flow. A quantitative calculation for the alternating and streaming components of fluid flow will be carried out, both with and without "active" processes. The bat and alligator lizard cochleas will be examined in detail. Understanding human hearing and the disorders will be advanced if the questions surrounding these specialized cochleas can be resolved.