Effect of basilar and tectorial membrane properties and gradients on cochlear response

The cochlea is a spiral-shaped, fluid-filled organ in the inner ear that converts sound with high resolution over a large frequency range to neurological signals that can then be interpreted by the brain. The organ of Corti, supported below by the basilar membrane and attached above to the tectorial membrane, plays a major role in the amplification of small signals. In early fluid-structure interaction models of the cochlea, the mechanical properties of the organ of Corti were neglected and only the basilar membrane was considered, approximated by a series of springs. Recent experiments suggest that the mechanical properties and property gradients of the tectorial membrane may also be important for frequency response of the organ of Corti and that separate waves may propagate along the basilar and tectorial membranes. Therefore, a two-dimensional two-chamber finite difference model of the cochlea was developed to investigate the independent responses of the basilar and tectorial membranes. Responses are compared for models using one-, two-, or three-degree-of-freedom approximations for the organ of Corti, with parameters derived from a physiologically based finite element model. The effects of independent coupling of the fluid to the tectorial and basilar membranes and longitudinal coupling along the membranes are investigated.