Electric currents in conductors with distributed capacity considered in relation to the propagation of the nerve impulse

Abstract

Nearly two centuries ago it was surmised that the nervous impulse might be of the nature of an electric current, but in the absence of definite proof the hypothesis was rejected, especially as objections were raised to it which seemed insuperable. It is difficult, if not altogether impossible, to reconcile all experimental results with the consequences of the molecular theory. If, however, we regard the nerve as an electrical conductor with distributed capacity, we are able to account for many of the fundamental experimental phenomena and also to predict the results of new experimental conditions. It has long been known that the speed of electricity on wires is less than the speed in free space and the formulá for calculating these velocities are well understood. The rate of propagation of electricity in a conductor similar in form, size and material to a nerve fiber should be, according to these formulá, of approximately the same order of magnitude as has been measured for the rate of the nervous impulse.

The enormous reduction of velocity (about ten million times) is chiefly attributable to the great ohmic resistance of the conductor coupled with the electrostatic capacity. As a result of measurements on the phrenic nerves of cats and calculations based on data of microscopic sections of nerves, we have been able to construct an artificial “nerve” of glass, paper, tinfoil and graphite, whose total resistance and capacity are of the same order of magnitude as those of the cat's nerve. On applying the break E.M.F. of an induction coil to this artificial nerve and leading off to a string galvanometer in the usual manner we have obtained typical diphasic curves almost identical with those obtained from cat nerves stimulated with the same current.