The Spark

Abstract

Using early microscopes, Leewenhoek and Fontana describe nerve fibres. Galvani discovers that electricity causes frog muscles to twitch, though the existence of “animal” electricity is doubted by Volta. Nobili is able to measure an injury current in muscle and Matteucci obtains dramatic, though indirect, evidence for some kind of impulse in muscle contraction. The impulse, or “negative variation,” is detected by du Bois Reymond with a sensitive galvanometer and its velocity in frog nerve is measured by Helmholtz using two methods. Hermann likens the structure and function of the nerve fibre to a series of electric components and his contemporary, Bernstein, invents an ingenious mechanical device for determining the brief time-course a the nerve impulse. Bernstein proposes that the difference in electrical potential across a resting nerve or muscle fibre membrane is due to unequal concentrations of potassium ions on the two sides, the membrane itself being semipermeable. Bernstein envisages the impulse arising because of a brief and unselective increase in membrane permeablility. Elsewhere Ranvier discovers interruptions in the sheaths of the myelinated nerve fibres.