THE END OF THE SPIKE POTENTIAL OF NERVE AND ITS RELATION TO THE BEGINNING OF THE AFTER-POTENTIAL

Abstract

The form of the axon spike potential has been followed to a point closer to its end than in previous determinations. The potential of the falling phase drops below 5% of that obtaining at the crest in about 3 crest times. In this region the rate of decline shows a sharp decrease so that the phase ends along a slowly decrementing curve and becomes indistinguishable at 20-25 crest times. When the potassium method is used for making the nerve monophasic, the potential recorded is found to be much freer of diphasicity than when the indifferent lead is produced by heat coagulation. The form of the monophasic spike obtained with the potassium method is shown. New evidence is given that in the ordinary "monophasic" lead the first phase outlasts the apparent position of the diphasic artifact. The wave which this causes in the records is labelled T. During at least 85-90% of the visible duration of the spike potential the nerve shows signs of the production of another potential very different in its general behavior, the after-potential. The after-potential has a rising phase. Like the total duration, this rising phase lasts for very variable times, according to the condition of the nerve. Its crest may occur at 3-4[sigma] (estimated) at the lower limit up to 60[sigma] or more at the upper (temp. range 20-25[degree] C, comparative value of spike crest-time 0.3[sigma]). Cooling causes a prolongation of the rising phase of the after-potential.