Layer thickness and curvature effects on otoconial membrane deformation in the utricle of the red-ear slider turtle: static and modal analysis.

Finite element models of otoconial membrane (OM) were developed to investigate the effects of three geometric variables on static and modal response of the OM: (1) curvature of the macular surface, (2) spatial variation in thicknesses of three OM layers, and (3) shape of the macular perimeter. A geometrically accurate model of a turtle utricle was constructed from confocal images. Modifying values for each variable formed variants of this model: modeling the macula surface as flat, OM layer thicknesses as spatially invariant, and the macular perimeter as a rectangle. Static tests were performed on each modified OM model, and the results were compared to determine the effects of each geometric variable on static mechanical gain (deflection per unit acceleration). Results indicate that all three geometric variables affect the magnitude and directional properties of OM static mechanical gain. In addition, through modal analysis, we determined the natural frequencies and displacement modes of each model, which illustrate the effects of the three geometric variables on OM dynamics. This study indicates the importance of considering three-dimensional OM geometry when attempting to understand responses of the OM and, therefore, the modulation of hair cell signals to accelerations during head movements.