Question

Contractile unit of muscle = sarcomere

2. a muscle cell = fiber

3. plasma membrane of the muscle fiber = sarcolemma

4. a long filamentous organelle with a banded appearance found within muscle cells = myofibril

5. actin- or myosin-containing structure = myofilament

6. cord of collagen fibers that attaches a muscle to a bone = tendon

Answer 1

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.