Semicircular Canals: Measurement of Endolymphatic and Cupular Displacements at Threshold

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Abstract
The left horizontal semicircular canal of the leopard frog (Rana pipiens) was exposed and the entire intact nerve was draped over a Pl-Ir hook for recording action potentials (AP). The preparation was rotated sinusoidally in the horizontal plane at 0.3 Hz, with varying angular displacements. The arm of the canal was transected, and a fine micropipette ligated in place in 1 end of the arm. Artificial endolymph was pumped into and out of the canal at the same frequency, while the amplitude of the displacement was varied from sub-threshold to supra-threshold values as determined from the resulting AP train. By comparing the 2 AP trains, it was determined that the movement of endolymph in the canals was 5.3 .times. 10-8 cm3/degrees per s, and that the threshold displacement of the midpoint of the cupula was 7.6 .times. 10-5 cm (0.76 .mu.m).