Exposure and direct stimulation of the semicircular canal cupula

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Abstract
The ampullary wall of the posterior semicircular canal was isolated from the frog, cut and the cupula exposed in frog Ringer's solution. The cupula was stimulated by depression with a fine glass micropipette. Three points on the cupula were selected for depression: point A, the lowest point on the midline of the cupula surface on the utricular side; point B, the uppermost on the midline of the same surface; and point C, in the middle of the lateral surface of the cupula. Depression at points A and B was toward the canal, whereas depression at point C was toward the centre of the cupula. The amount of depression was controlled by a micromanipulator. At point A, the minimum depression facilitating the posterior canal action potential was 1 μ; at point B, a greater amount of depression was needed to produce the action potential. Even a large amount of depression at point C resulted in only a small action potential, possibly because the direction of the sensory cell polarity is along the long axis of the canal.