An experimental study on the physiological significance of the mode of cupular movement

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Abstract
Isolated frog posterior semicircular canals were used. The ampullary nerve action potentials were recorded under three kinds of cupular movement, i.e., swing-door deflection, “cupula fixation-1” and “cupula fixation-2”. Cupula fixation-1 was achieved by immobilizing the central top portion of the cupula, while cupula fixation-2 was achieved by immobilizing the entire top of the cupula. Cupula fixation-1 resulted in action potentials which were comparable to those of the swing-door deflection in terms of the maximum spike count and the stimulus-response curve. Cupula fixation-2 resulted in potentials with the maximum spike count comparable to the swing-door deflection; however, the response increase rate was very low. The time courses of the potentials in those cases of cupula fixation-1 and -2 were extremely short (about 2–3 s) when compared to that of the swing-door deflection. These findings suggest that the swing-door deflection is physiologically more relevant in giving the optimum increase in response rate, as well as maintaining the time course of the tonic response.