The final element of a pump is a rhythm generator, or a metronome. Physiologists found that specialized nerve-like cells, resident in the heart, generate paced, rhythmic electrical impulses that stimulate the contraction. Yet other nerves—fast-conducting electrical wires—carry these impulses throughout the heart, first to the atria, and then to the ventricles. Once the impulse reaches one cell, the junctions between the cells ensure that all cells contract together.
