Final answer:
A single muscle cell is known as a muscle fiber, which contains hundreds to thousands of myofibrils. The muscle fiber is encased in a plasma membrane called the sarcolemma and contains cytoplasm or sarcoplasm. Sarcomeres within myofibrils facilitate muscle contraction.
Step-by-step explanation:
A single muscle cell is called a muscle fiber. These are the individual cells that make up skeletal muscle tissue. Each muscle fiber is surrounded by a plasma membrane known as the sarcolemma, with a cytoplasm called the sarcoplasm. Muscle fibers are incredibly large cells, containing hundreds to thousands of myofibrils. Myofibrils are the long cylindrical structures that run parallel to the muscle fiber and give the muscle its striated appearance.
Within each muscle fiber, myofibrils are organized into units called sarcomeres, which is the smallest contractile portion of muscle tissue. The repeating units of sarcomeres along a myofibril are what lead to muscle contraction. Muscle fibers consist of myofilaments composed of the proteins actin and myosin organized in sarcomeres, allowing for the muscle contraction mechanism that is vital for movement.