THE IRRITABILITY CHANGES IN NERVE IN RESPONSE TO SUBTHRESHOLD CONSTANT CURRENTS, AND RELATED PHENOMENA

Abstract

By methods involving direct registration of ampliF1ed action potentials with the cathode ray oscillograph, determinations have been made of the irritability of nerve as affected by short periods of subrheobasic polarization. At the cathode the irritability upon the make rises along an upwardly convex curve to a plateau, which, at about 2 sigmas, is terminated abruptly by a decline in irritability, concave upwards, which approaches asymptotically the level maintained by the polarization. The fall from this level begins slightly before the break of the constant current; this preterminal fall can be accounted for by assuming that the axons are responding to the testing induction shocks with latencies ranging through this preterminal interval. The possibility is considered of an interrelation between latent period and summation interval. The break of the constant current is followed by the period of postcathodal depression which has about the same duration as the relatively refractory phase and varies in depth and duration as the depression following the plateau on the make. In nerve that is being polarized cathodally by a current rising at less than the liminal rate, irritability F1rst rises, but F1nally falls and becomes subnormal due to cathodal depression. The rising phase as well as the falling phase of the axon action potential is abbreviated by cathodal polarization.