QUANTITATIVE STUDIES OF THE NERVE IMPULSE

Abstract

The action currents from cats'' excised peroneal nerves, exposed at room temp. to varying concentrations of CO2, were recorded by means of a string galvanometer. The initial excursion of the galvanometer, representing total current flow over a period of several sigmas, shows a definite increase as the CO2 tension in the atmosphere surrounding the nerve is increased to about 20 mm. At higher tensions the response is progressively less, until at about 55 mm. the response is less than at very low tensions. Control observations show that the changes recorded reflect alterations in the average response of the individual fibers and not in the number of fibers active. The average increase in response at the optimum CO2 tension (about 20 mm. Hg) is 20-30%. The action currents of nerves exposed to CO2 show a prolonged falling phase. The string may not return to its base line for 1/10 of a second or more. The effective E.M.F. 10<r after the beginning of the electric response may be of the order of 1 mv. This "action current remainder" is greatest at CO2 tensions between 20 and 50 mm. At certain concentrations of CO2, the primary action current is diminished while the "action current remainder" is increased. This suggests that they are the electrical expressions of different and more or less independent processes. No marked "treppe" effects could be detected, and the evidence does not support the theory that central summation may be due to local accumulation of CO2.