THE IRRITABILITY CHANGES IN NERVE IN RESPONSE TO SUBTHRESHOLD INDUCTION SHOCKS, AND RELATED PHENOMENA INCLUDING THE RELATIVELY REFRACTORY PHASE

Abstract

The changes in irritability incident to the stimulation of nerve [sciatic of Rana pipiens] with a subthreshold induction shock are followed, using as an index the action potential of the nerve, observed, after amplification, on the cathode ray oscillograph. The duration of the 1st, or positive, phase, or summation interval is not affected by shock duration when the latter is sufficiently brief; but the duration of the summation interval is influenced by the strength of a subthreshold shock of any given duration. Duration also varies with temp., and is longer in cathodally polarized than in normal nerve. It is definitely demonstrated that the summation interval can outlast the applied shock potential and varies independently of the electrical artifacts. It has no recognizable electrical sign. The 2nd or depression phase returns to the normal level asymptotically in a period that seems to increase with the strength of the sensitizing shock, but at 28-15[degree] C. approaches in duration the relatively refractory phase as a limit. When the subthreshold sensitizing induction shock is anodal instead of cathodal the entire irritability picture is inverted, the terminal phase being one of enhanced instead of depressed irritability. The 2nd phase following a cathodal shock, therefore, is regarded as a state of post-cathodal depression. Since the depression interval left by a just subthreshold cathodal shock is coterminal with the relatively refractory phase, the latter also is regarded as a state of postcathodal depression left in this case by the nerve''s action potential. This interpretation is supported by the observation that the relatively refractory phase can be almost abolished by a properly placed anodal shock. The "after-effect" of Kato that is left by a blocked nerve impulse, the repetition of which is believed by him to produce Wedenski blocking, therefore is to be regarded as a state of postcathodal depression and the Wedenski block as a state of maintained postcathodal depression.