RESPONSES OF A NODE OF RANVIER TO DIRECT REPETITIVE STIMULATION

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Abstract
Applying repetitive stimuli to a single node of Ranvier of a myelinated nerve fibre of the toad, the relation between the response and the stimulus strength and frequency were investigated. 1) The case of subthreshold repetitive stimulation. Several local responses'' (L.R.) appeared prior to the first spike. The L.R. became gradually larger in size towards a certain maximal value where a spike was fired suddenly. After the first spike, the same thing took place before the second spike appeared, or else each of the successive stimuli did evoke a spike, according to the stimulation frequency. The spike height appeared smaller when preceded by a larger number of local responses. The spike height got smaller while the maximal L.R. became larger with time, especially in high stimulation frequency. 2) The case of weak suprathreshold repetitive stimulation. In very high frequency stimulation, one and just one spike was evoked. The value of Q in the final steady state got smaller with higher stimulation frequency. The case of strong repetitive stimulation. The spike appeared reduced in size when elicited by a stimulus more than several times stronger than the threshold. Just one spike was evoked in very strong repetitive stimulation. A possibility was shown that the same phenomena such as Wedensky''s inhibition on a narcotized region can be the case also in a normal fibre. The ratio Q as a safety factor of conduction was confirmed.