Acting on Impulses

Sherrington's work fed directly into that of Edgar Adrian, the scientist he shared the 1932 Nobel Prize with, and also that of Herbert Gasser and Joseph Erlanger, who received the Physiology or Medicine Prize in 1944.

By the 1920s, scientists felt sure that nerve signals were electrical, and that nerves behaved like wires. Indeed, back in 1859, the ingenious German physicist Hermann van Helmholtz had actually managed to time the speed that electricity buzzes down an axon. Yet electricity in nerves seemed strangely slow, crawling along only at 90 feet per second - while electricity in a wire travels millions of times faster at close to the speed of light (186,000 miles per second). In fact, electricity in a nerve is not like an electric current at all. An electric current is a rapid flow of electrons, but electricity sweeps along the nerve as an 'action potential', a difference in electrical charge between the inside of the nerve and the outside.

Amazingly, Adrian, Gasser and Erlanger found ways to connect wires to nerves and amplify the signal so that they could make an action potential fire off a sound in a loudspeaker, or create a light trace on the screen of an 'oscilloscope'. Adrian, as he listened to his loudspeaker, found that nerve signals are very simple, just going: bang! on, then bang! off. And to his surprise, a stronger stimulus increased only the number of nerve impulses that are produced every second, not the actual size of the impulse.

Watching on their oscilloscope, Gasser and Erlanger detected that impulses had slightly different patterns in three kinds of nerve fibre, with both touch and muscle movement signalled rapidly through thick fibres and pain signalled more slowly through thinner fibres. It began to become clear that nerve signals are very simple; it is the way nerves are wired up that determines the message, not the nature of the signal.

Detecting different nerve impulses


Joseph Erlanger sitting at the oscilloscope device that he and Herbert Glasser built to amplify and visualize nerve impulses, or action potentials, as they travel along a neuron. Using their device, Erlanger and Glasser discovered that different types of nerve fibres conduct impulses at different rates, which relates to their particular function.
Courtesy of the Bernard Becker Medical Library.

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