REPETITIVE STIMULATION OF A NODE OF RANVIER UNDER ELECTROTONUS

Abstract

Employing toad's myelinated fibres as material, the responses of a single node of Ranvier to direct repetitive stimulation were examined. The chief results obtained are as follows:
1. The spike height gets larger (smaller) and the duration gets shorter (longer) in A. E. T.(C. E. T.).
2. Generally, the spike height gets gradually smaller with time. The rate of decrease is larger (smaller) than normal under C. E. T.(A. E. T.).
3. Repetitive subthershold stimulation under C. E. T. evokes a spike after evoking several local responses, as in normal conditions. Thereby, the necessary number of stimulus decreases with strength of C. E. T. towards “one”. The size of the spike is a little larger when evoked after repetition of stimulus than when evoked by a single stimulus (FIG. 4, C. E. T.). Under A. E. T., on the other hand, a just suprathreshold stimulus becomes subthreshold, the number of stimulus necessary for initiation of spike increases with strength of the tonus, until finally just local responses are produced without evoking any spike. The size of thespike is somewhat larger when evoked by a single stimulus than when evoked by some repetitive stimuli (FIG. 4, A. E. T.).
4. The local response can be summated in sufficiently high frequency stimulation.
5. 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.
6. There are differences between the attitudes of spike and local response to stimulation under E.T at least with regard to the response size
7. 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.