Multi-scale model of cochlear mechano-transduction.

<p>Three different physical problems are solved simultaneously: 1) cochlear fluid dynamics, 2) structural mechanics, and 3) outer hair cell electro-physiology. When the oval window was stimulated by a pure tone at 2.2 kHz, fluid-dynamical, structural, and electro-physiological responses were simulated. (<b>A</b>) The cochlear cavity was represented by a fluid-filled rectangular chamber divided into top and bottom fluid spaces by the elastic OCC. (<b>B</b>) Cochlear fluid dynamics was reduced to a 2-D domain (mesh size 10 μm in the x- and z- directions). The 2-D fluid domain interacts with the top and bottom surfaces of the 3-D OCC represented by the TM and the BM. The color contour represents pressure gain: (|<i>p</i>| - |<i>p</i>_<i>HT</i>|)/|<i>p</i>_<i>OW</i>|, where <i>p</i>_<i>HT</i> and <i>p</i>_<i>OW</i> are fluid pressures at the helicotrema and the oval window, respectively. (<b>C</b>) The OCC structure. Besides the BM and the TM, hair cells, pillar cells and Deiters cells are mechanically significant. (<b>D</b>) The 3-D finite element model of the OCC incorporated realistic geometrical and mechanical characteristics of the gerbil cochlea. The OCC micro-structures repeat with the longitudinal grid size of 10 μm. (<b>E</b>) Two reactive forces were incorporated with the outer hair cells—the force originating from mechano-transduction in the hair bundle (<i>f</i>_<i>MET</i>) and the electromotility of the cell membrane (<i>f</i>_<i>OHC</i>). (<b>F</b>) Mechanical (BM, TM and hair bundle displacements) and electrical (outer hair cell membrane potential change ΔV_OHC) responses over a cycle.