The largest unit of a skeletal muscle is known as the muscle belly. The muscle belly is composed of many units called fascicles which comprise of bundles of muscle fibers (also known as muscle cells). Muscle fibers are filled with myofibrils - filaments containing contractile proteins. These contractile proteins are arranged in repeating units known as sarcomeres, which give skeletal and cardiac muscle tissues their striated appearance.
Figure 1: The architecture of a skeletal muscle.
The architecture of the muscle influences skeletal muscle activity. Skeletal muscle tissue contracts rapidly and with great force, but it also tires very easily and must rest after short periods of activity. Cardiac muscle tissue, on the other hand, contracts constantly without our conscious influence.