Tetany (action potential summation)

Tetany is the point at which signals from nerves (action potentials) are arriving to skeletal muscle rapidly enough in succession to cause a steady contraction, and not just a series of individual twitches.

Tetany can be demonstrated by applying quick electrical charges to the skin close to where a nerve lies (such as by the elbow near the ulnar nerve). If these charges are coming once a second, the hand muscles (which the ulnar nerve supplies) will flex once a second. If the frequency is increased, the hand will close up, and individual twitches will not be seen.

To move a muscle, the brain sends an action potential to the muscle at a very fast rate, and the muscle contracts smoothly.