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

1972; Elsevier BV; Linguagem: Inglês

10.1016/s0079-6123(08)63926-6

1875-7855

Charles M. Oman, Laurence R. Young,

Motor Control and Adaptation

This chapter addresses the question of what constitutes the “physiologic” behavior of the cupula. Considerations based on calculation of the moment of inertia of endolymph in the membranous semicircular canal and on known behavioral responses to angular accelerations suggest that the pressure across the cupula associated with behavioral thresholds must be less than 10–4 dyne/cm2. Calculation of the density gradient pressures resulting from threshold level caloric stimulation yields results consistent with this figure. These calculations result directly from the known morphology of the canals, and involve no assumptions with respect to cupula stiffness or cupula drag. The cupula constitutes of a biological pressure transducer with a threshold of the same order as that of the auditory system. The calculations also suggest that it would be extremely easy to traumatize the cupula structure 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 range of cupula motion is also obtained from theoretical considerations in this chapter. Conservative calculations indicate that the cupula midpoint moves only about 10-2 μm at the 0.1º/sec2 acceleration levels commonly associated with behavioral thresholds. Accelerations of 30º/sec2 or velocity changes of 600º/sec, which are typical of maximal self-induced head motions, should produce cupula midpoint motions no greater than about 3 μm.