What occurs when a motor unit is stimulated by a single nerve impulse?

When a motor unit is stimulated by a single nerve impulse, it results in a twitch. A twitch is the brief contraction and relaxation of a muscle fiber or group of fibers in response to a single action potential from a motor neuron. This type of muscle response involves the release of calcium ions, which facilitates the interaction between actin and myosin filaments, leading to the muscle contraction.

A twitch is characterized by a rapid rise in tension followed by a quick decline, reflecting the brief nature of the stimulus. It is an essential component of muscle physiology, demonstrating how muscle fibers respond to neural signals.

In contrast, tetanus refers to a sustained muscle contraction that occurs when a series of rapid stimuli are provided, leading to a state of continuous contraction. Summation involves the increase in muscle tension due to successive stimuli occurring in quick succession, resulting in a stronger contraction compared to a single twitch. Contraction is a general term describing the process of muscle shortening and tightening but does not specifically denote the reaction to a single nerve impulse.