Electricity and the Nervous System

In the tradition of Galvani and Aldini, Carlo Matteucci used a newly developed galvanometerGalvanometer to record a current flow between the cut and intact surface of a frog nerve or muscle that he called the demarcation current. The cut surface had a negative potential relative to the intact surface. Emil du Bois-Reymond identified the electrical event associated with nerve excitation of muscle that he called the negative variationNegative variation, later known as the action potentialAction potential. Herman Helmholtz measured the speed of the action potentialAction potential as it moved down the nerve to the muscle and it was surprisingly slow (about 30 m/s) compared to the speed of electricity moving along a wire. His student Julius Bernstein showed that the action potentialAction potential lasted about 1 ms and its time course was independent of the stimulus strength. The debate over localized versus generalized function of the cerebral cortex was convincingly resolved by clinical–pathological studies in patients and electrical stimulation of the brain in primates. Functions were clearly localized within the cerebral cortex. Finally, Charles Sherrington used electrical stimulation of the spinal cord to study the integrative function of the nervous system. He introduced the concept of a synapseSynapses and showed how complex behaviors such as walking and scratching could still occur in a rudimentary form after the spinal cord had been resected from the brain.