Question

a tubular network around each myofibril is the
sarcomere.
sarcoplasmic reticulum.
endomysium.
sarcoplasm.
sarcolemma.

Explanation:

• Sarcomere: It is the basic contractile unit of a myofibril, composed of actin and myosin filaments, not a tubular network.
• Sarcoplasmic reticulum: A specialized endoplasmic reticulum in muscle cells. It forms a tubular network around each myofibril and is involved in storing and releasing calcium ions, which is crucial for muscle contraction.
• Endomysium: A layer of connective tissue that surrounds individual muscle fibers (not a tubular structure around myofibrils).
• Sarcoplasm: The cytoplasm of a muscle cell. It is the fluid - like substance within the muscle cell that contains various organelles and is not a tubular network.
• Sarcolemma: The plasma membrane of a muscle cell. It is a single - layered membrane (not a network of tubules) that surrounds the muscle cell.

Answer:

sarcoplasmic reticulum.