REPETITIVE STIMULATION OF A NODE OF RANVIER UNDER ELECTROTONUS

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Abstract
Employing toad''s myelinated fibres as material, the responses of a single node of Ranvier to direct repetitive stimulation were examined. The spike height gets larger and the duration gets shorter in A.E.T. The reverse changes take place during catelectrotonus. Generally, the spike height gets gradually smaller with time. The rate of decrease is larger than normal under C.E.T. and smaller during anelectrotonus. Repetitive subthreshold stimulation under C.E.T. evokes a spike after evoking several local responses, as in normal conditions. Thereby, the necessary number of stimuli decreases with strength of C.E.T. towards "one". The size of the spike is a little larger when evoked after repetition of stimulation than when evoked by a single stimulus. Under A.E.T., on the other hand, a just suprathreshold stimulus becomes subthreshold, the number of stimuli necessary for initiation of spike increases with strength of the tonus, until finally only local responses are produced without evoking any spike. The size of the spike is somewhat larger when evoked by a single stimulus than when evoked by repetitive stimuli. The local response can be summated during stimulation of sufficiently high frequency. There is some after-effect of electrotonus upon the spike height. It is the same, not reversed, in quality with the effect during the tonus-on. There are differences between the attitudes of spike and local response to stimulation under E.T., at least with regard to the response size. The ratio Q (spike height/max. L.R. height) was large in long pulse stimulation and in A.E.T., and smaller in short pulse stimulation and in C.E.T.