Sustained contraction is called
II. Muscles in vitro can exhibit twitch, summation, and tetanus. A. The rapid contraction and relaxation of muscle fibers is called a twitch. B. A whole muscle also produces a twitch in response to a single electrical pulse in vitro.1. The stronger the electric shock, the stronger the muscle twitch, whole muscles can produce graded contractions.2.. The motor neuron and the muscle fibers it innervates are called a motor unit. 1. When a muscle is composed of many motor units (such as in the hand), there is fine control of muscle contraction. 2. The large muscles of the leg have relatively few motor units, which are correspondingly large in size.