Muscle tissue accounts for nearly one-half of the total body weight and consists of three distinct subtypes:
• striated (skeletal) muscle
• smooth (visceral) muscle, and
• cardiac muscle
Each type of muscle cell is designed to perform one basic function.
Striated muscle is attached to bones that move the skeleton.
Smooth muscle is located in the walls of hollow internal structures, such as the intestines and blood vessels, allowing such organs to expand and contract.
Cardiac muscle occurs only in the heart, where it forms the walls and enables the heart to pump blood. When viewed under the light microscope, striated muscle cells appear long and thread-like with alternating light and dark cross strips called striations. In contrast, smooth muscle has no striations, Cardiac muscle cells, each of which has a nucleus, are slightly striated. Each cardiac muscle cell tends to divide into a "y" or "x" shape, so that it has more than two ends and joins more than two other cells, i.e., it intercalates. The ends of one cardiac muscle cell are separated from adjoining cells by a band called an intercalated disk.
Unlike skeletal muscle, smooth muscle and cardiac muscle are controlled involuntarily, i.e., an individual cannot stop or start the muscle action.
highly cellular and well vascularized