Models of the structure and motility of the auditory outer hair cell

The objective of this research is to determine the mechanical properties and structural role of the mammalian auditory hair cell. The outer hair cell is essential to the biophysical process of hearing. It contributes to both the frequency selectivity and dynamic range with which we are able to perceive sound. The primary role of the outer hair cell is to modify the mechanical motion within the cochlea, enhancing the motion due to low amplitude sound and giving better resolution between different frequencies. The outer hair cell fulfills this role through unique 'electro-motile' properties which allow the cell to undergo large length changes due to small changes in electrical potential. The length changes actively modify the stiffness of a local region of the cochlea, and thereby modify the vibration response due to acoustic stimulus.;Experiments on isolated outer hair cells from guinea pigs are performed which describe the static material response of the cell wall to various stimuli. These experiments are designed to illuminate the role of the microstructure and nanostructure within the cell wall. Of particular interest are the properties the lateral plasma membrane which has recently been identified as the source for the cell 'electro-motility'. A static piezoelectric model is developed for the cell wall deformation behavior. The model is shown to reproduce and predict accurately the experimentally measured cell deformation behavior reported from numerous research laboratories.;A dynamic model of the cell is developed which incorporates the viscous fluid interaction of the cell with both intracellular and extracellular fluid. Fourier analysis techniques are used to predict the frequency response of the cell under various load and boundary conditions. The results of the dynamic analysis indicate that the piezoelectrically driven cell deformation can operate at frequencies in excess of 25 kHz without substantial attenuation. This supports the proposition that the outer hair cell actively modifies the stiffness of the cochlear partition at acoustic frequencies on a cycle by cycle basis.