Final answer:
The cell membrane of a muscle fiber is called the sarcolemma, which encases the sarcoplasm and is key to action potential conduction and muscle contraction.
Step-by-step explanation:
The cell membrane of a muscle fiber is known as the sarcolemma. This membrane surrounds the skeletal muscle fiber and plays a critical role in the conduction of action potentials, which are necessary for muscle contraction. Within the sarcolemma is the cytoplasm of the muscle cell, called the sarcoplasm. Muscle fibers contain many fibrils, and these are organized into units called sarcomeres, which are responsible for the striated appearance of the muscle and are essential for muscle contraction. It's important not to confuse the sarcolemma with the sarcoplasm or sarcoplasmic reticulum, which also play roles in muscle function but are distinct components within the muscle fiber.