Recovery course of excitability in a single neurone of Onchidium verruculatum.

Abstract

ABSTRACT The electrical excitability of a nerve cell of Onchidium verruculatum was measured by transmembrane depolarizing current pulses through a glass-capillary microelectrode inserted into the soma of the nerve cell. The strength-duration and the strength-latency relations were measured during the resting state of a silent-type nerve cell, and both were represented by hyperbolic curves. This shows that the minimum quantity of electricity (that is, current strength multiplied by time duration required to produce a spike) must pass through the membrane to discharge impulses in the resting state of the nerve cell. The strength-latency relations were obtained after a spontaneous spike. The stimulus began during the falling phase of a preceding firing and lasted for 300 ms. These relations were represented by two exponential terms. The strength-duration relations were measured at various times after a preceding discharge and these were also represented approximately by hyperbolic curves in regularly firing or frequently firing neurones. These results suggested that a minimum quantity of electricity must be required to elicit a second spike at a given time interval after a preceding spike; and that the reciprocal of this value might represent the excitability after that time interval. The time course of the reciprocal of the quantity referred to above expresses the process of the recovery of excitability in the nerve cell after a spike. This process can be expressed mathematically by two exponential terms.