Final answer:
A muscle fiber is surrounded by a sarcolemma and contains myofibrils organized into sarcomeres, which house thick myosin and thin actin myofilaments essential for muscle contraction.
Step-by-step explanation:
Skeletal muscle fibers are specialized cells with a key role in body movement. A muscle fiber, also known as a myocyte, is enclosed by a plasma membrane known as the sarcolemma, containing a cytoplasm termed sarcoplasm. Within these fibers, myofibrils run the length of the cell and anchor to the sarcolemma, giving it a striated appearance. Myofibrils are composed of repeat units called sarcomeres, the contractile units of the muscle, which contain the myofilaments actin and myosin.
Myofibrils exhibit a banded pattern due to the organization of these myofilaments. Thick myofilaments consist of myosin while the thin ones are composed of actin, troponin, and tropomyosin. The sarcoplasmic reticulum (SR), a specialized form of endoplasmic reticulum, is involved in the storage, release, and uptake of calcium ions (Ca++), crucial for muscle contraction and relaxation processes.