Microscopic Anatomy and Contraction of Skeletal Muscle. We have already examined the structure of skeletal muscle as seen with the light microscope. As you know, skeletal muscle tissue has alternating light and dark bands, giving it a striated appearance. The electron microscope shows that these bands are due to the arrangement of myofilaments in a muscle fiber
Only cardiac muscle has this particular appearance, which is given to it by something called intercalated discs. Cardiac muscle also consists of single muscle cells, called Cardiomyocytes; where something such as skeletal muscle cells are MULTInucleated (more than one cell nucleus).
Muscle contraction and relaxation. Interdigitation of thick and thin filaments allows sarcomere contraction, which is best explained by the sliding filament model in which actin filaments slide along myosin filaments. During contraction, both sets of filaments retain their normal length, A bands remain unchanged in length, I bands shorten, and H zones are narrowed.