The Physiological Range of Pressure Difference and Cupula Deflections in the Human Semicircular Canal: Theoretical Considerations

Abstract

The question of what constitutes the “physiologic” behavior of the cupula has been the subject of debate for some time. Calculations are presented which suggest that the cupula constitutes a biological pressure transducer with a threshold of the same order of magnitude as that of the auditory system. This indicates that it would probably be extremely easy to traumatize the cupula by exposing it to pressure gradients far beyond its normal dynamic range in the course of experimental preparations intended to visualize cupula motion. An estimate of the dynamic range of cupula motion may also be obtained which indicates that the center of the cupula may move as little as ten millimicrons at the 0.1 deg/sec² acceleration levels commonly associated with behavioral thresholds. Accelerations of 30 deg/sec² or sudden velocity changes of 600 deg/sec, typical of maximal self-induced head motions should produce cupula midpoint motions no greater than about three microns. Because of the small dynamic range of cupula motions, modes of cupula deflection other than rotation about the crista cannot be ruled out, because they are indistinguishable from a dynamic point of view.