 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. Yejvo time here, 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 tropomyosine of the sites of actin and cross bridges formation. 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 fibers. In some it may be as short as only 10 microseconds, 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. Yehnike ek muscle mussel cell continuously contracting halat me rehhta hain aur relax mukamal tor pa relax nahi hota. There are two types of muscle tension or tetanic contractions. Unfused that is incomplete tetanus and fused that is complete tetanus. An unfused tetanus occurs when the muscle is being stimulated at a relatively faster rate. So the fibers do not completely relax between the two effect of two stimuli. Ek stimulus aia usk enti jme muscle me contraction hui uske baad usne relax karna shru kia. Lekin issi doran me dosa stimulus aage lehada relax nahi hua mukamal tor pa aur phe contact ho gaya aur yun zyada halat uski contraction me rehhegi and this is called the unfused or incomplete tetanus. When there is absolutely no relaxation between the stimuli and relaxation 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 which is to the level which is its maximum possible contraction.