Excitation and accommodation in nerve

Abstract

Electric current passed through a nerve changes its "local potential" from Vo, the resting value, to V. The critical value of V required for excitation, the threshold U, rises gradually during the passage of the current in consequence of and at a speed detd. by the change in V, and may rise while V is maintained constant. For excitation to occur, V must equal U. There are thus 2 time factors in excitation, rate of change of V and rate of change of U. Both U and V revert independently to their initial values Uo and Vo when the current is withdrawn. Evidence is advanced that they do so exponentially, according to the equations[long dash] dV/dt = (V[long dash]V0)/k and[long dash]dU/dt = (U[long dash]Uo)/[lambda]. k is the time-constant of the process whereby V tends to decay to its initial value, [lambda], the time-constant of the decay of "accommodation," the rate at which the threshold falls. Where the time required for excitation is very short, k only is involved. (U[long dash]Uo) can be calculated by integration for any form of applied current, so that from these conceptions it is possible to calculate, with experimentally observed quantities and in absolute units: (a) the form of strength-duration curve, (b) the conditions for excitation at break or ab gap in constant current, (c) utilization time for any form of current, (d) the effects of accommodation on the rheobase and chronaxie, (e) the relation between final intensity and time of rise with linearly increasing currents and the slope of the minimal current gradient, (f) the relation between final intensity and time-constant of rise with exponentially increasing currents, (g) the relation between strength and frequency with alternating current, and the position of optimum frequency, (h) the changes of excitability with sub-threshold currents, (i) the lowered excitability during high-frequency one-way stimulation. While no assumptions as to the physical or chemical nature of U and V are made, a simple hydraulic model is described which will obey the equations developed in this paper. X is shown to be the same thing as Fabre''s "constante lineaire," Schreiver''s Einschleichzeit (multiplied by 2.69), and Monnier''s t2. Monnier''s "etat d''excitation" is (Uo[long dash]Vo)[long dash](U[long dash] V). [lambda] is affected by temp.and Ca-ion concn.