Answer
The three phases of a skeletal muscle twitch are the latent or lag phase, the contraction phase, and the relaxation phase;
The latent period. This is the period from the onset of the stimulus to the beginning of contraction of the muscle fiber. During this period excitation of the muscle fibers takes place; excitation contraction coupling takes place, and elastic components of the muscle become taut.
The contraction phase. This is the period in which and external tension rises and peaks . The force developed by the muscle moves a load or resists tension. The contraction phase is short-lived because the sarcoplasmic reticulum quickly reabsorbs the Ca++ ions it released into the cytoplasm before the myofibers develop maximal force, As the [Ca++] concentration of calcium ions in the cytosol declines , myosin molecules release actin filaments, and muscle tension begins to decline. The contraction phase is about 26 ms; it is shorter than the relaxation period.
Work Step by Step
Relaxation phase. This phase begins at peak tension and lasts for about 100 ms. During this time the muscle fiber slowly returns to near original length.
