Final answer:
A muscle fiber is the cellular unit of muscle, composed of myofibrils. It is surrounded by the sarcolemma and contains the sarcoplasm.
Step-by-step explanation:
A muscle fiber is the cellular unit of muscle. It is composed of many myofibrils, which are packaged into orderly units. The plasma membrane surrounding the muscle fiber is called the sarcolemma, and the cytoplasm is called the sarcoplasm.