Abstract
A precise balance of cupula and endolymph densities is key to the proper sensing of angular acceleration by the semicircular canals (SC). Estimates show that a density difference of cupula and endolymph (DD) as small as ~10 − 4 g/cm3 is sufficient to make the SC sensitive to gravity and centrifugal forces provided they are comparable with gravity. As a result this might cause vestibular disorders. There are conditions under which the DD may even exceed this value. One of them is a change of intra-labyrinth pressure (IP) that may take place during a spaceflight. Here, the effect of DD on SC dynamics is considered using a simplified one-dimensional toroidal mathematical model of a canal for rotation with constant or harmonically oscillating angular velocities. The DD results in: dependence of cupula dynamics on orientation of both the gravity vector relative to the SC plane and the axis of rotation, as well as on the distance between the axis of rotation and the center of SC; shift of the cupula to a new position of equilibrium that depends on both the gravity vector and the parameters of head rotation; and onset of cupula oscillations with multiple frequencies under harmonic stimulation. The DD effect may be important under conditions of artificial gravity where the directions of centrifugal forces, the values of which are comparable with Earth’s gravity, the orientations of the axis of rotation of a space station, and the axes of the SCs change during movements of the individuals and their habitat.
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Kondrachuk, A.V., Boyle, R.D. The Density Difference of Cupula and Endolymph Changes the Mechanics of Semicircular Canals. Microgravity Sci. Technol. 23, 433–438 (2011). https://doi.org/10.1007/s12217-011-9265-6
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DOI: https://doi.org/10.1007/s12217-011-9265-6