Mechanics of the otolith organ--dynamic response.

The otolith organs are the linear motion sensors of the mammalian system. As part of the vestibular system, these small organs are located in the inner ear. Mathematically modeled, they consist of an overdamped second-order system with elastic, viscous damping and mass elements. The governing equations of motion which describe the relative velocity of the mass with respect to the skull consist of a set of three coupled partial integral-differential equations. When these equations are nondimensionalized, they yield two nondimensional parameters which characterize the dynamic response of the system. These nondimensional equations are solved numerically for the relative displacement of the otolith mass for various values of the two nondimensional parameters. The solutions generated are for a step change in skull velocity. These solutions indicate that the end organ upper breakpoint frequency is at least one order of magnitude higher than previously measured experimental values determined by first-order neuron recordings.