 Dear students, in this topic, we shall discuss the muscle twitch and muscle tetanus. Dear students, a muscle twitch is a single contraction that is produced in response to a single action potential. There are three components of a single muscle twitch. Number one, the latent period or leg phase. Number two, the contraction phase. And number three, the relaxation phase. First we shall discuss the latent period, which is a short delay from the time when an action potential arrives at the muscle until a tension is observed in the muscle. This is the time which is required for the calcium ions to diffuse out of the sarcoplasmic reticulum and to bind these calcium ions to troponin and the moving of tropomyocene of the sites of acting and cross bridges formation. After this, contraction begins. The muscle in the contraction phase generates tension. This contraction phase is associated with the cycling of the cross bridges which result in the shortening of sarcomeres. Then comes the relaxation phase, in which the muscle returns to its normal length. Dear students, the length or time of a twitch varies in different types of muscle fibres. In some, it may be as short as only 10 milliseconds or as long as 100 milliseconds in other cells. Dear students, now we shall discuss the muscle tetanus. Muscle tetanus is a sustained muscle contraction which is produced by stimulation from simultaneous and multiple impulses. During the tetanised state, the contracting tension in the muscle remains constant in a steady state i.e. a muscle continuously stays in a contracting state and does not relax at all. There are two types of muscle tension or tetanic contractions. Unfused i.e. incomplete tetanus and fused i.e. complete tetanus. An unfused tetanus occurs when the muscle is being stimulated at a relatively faster rate. So the fibres do not completely relax between the two effect of two stimuli. One stimulus occurs when the muscle is being stimulated at a relatively faster rate. This is called the unfused or incomplete tetanus. When there is absolutely no relaxation between the stimuli and contraction, then the twitches overlap and muscle remains in continuous contraction. This is called fused or complete tetanus. It happens when the stimulation is received at a very high frequency. In the fused tetanus state, the muscle contracts to the level which is its maximum possible contraction.