Nerve impulses are signals carried along nerve fibers. These signals convey, to the spinal cord and brain, information about the body and about the outside world. They communicate among centers in the central nervous system and they command your muscles to move.

Nerve impulses are electrochemical events. Observed as an electrical event, a nerve impulse is called an action potential (AP) because it involves a change in electrical potential that moves along the nerve cell. It can be measured as an electrical potential difference between the inside and the outside of a nerve fiber. That option has not been generally available to the beginning student. Instead, the nerve impulse has ordinarily been observed as a voltage change along the outside of the sciatic nerve of the common grass frog, Rana pipiens.

Rana pipiens and its relatives have long been favorite subjects for introducing students to the physiology of nerve and muscle. For serious investigations, use of frogs will continue to be justified, but the consumption of this resource for routine teaching ought now to be reduced, for at least three convincing reasons:

1. Computing power has become so effective and so generally available that some essential concepts of nerve electrophysiology can as well or better be conveyed by simulation and example rather than by use of live material.
2. In the frenzy of trying to make the real specimen perform properly during a student exercise, important ideas are often omitted or are lost because of equipment failure or operator ineptitude.
3. Frog populations worldwide appear to be diminishing at an alarming rate, and biologists, of all people, ought not abet this decline.

Topics 1-11 afford a review of some aspects of single-neurone transmembrane characteristics. With this background,the student is prepared to appreciate the whole-nerve behavior illustrated in topics 12-30. The latter are based on actual cathode-ray-oscilloscope records of the type obtained by students in a laboratory course.