What is the plasma membrane of a muscle fiber?

• A. Sarcolemma
• B. Sarcoplasm
• C. Myoglobin
• D. Sarcoplasmic reticulum

Answer: (A)

The sarcolemma is the plasma membrane of a muscle fiber. It surrounds the muscle cell interior, helping to maintain the cell’s structure and housing the ion channels and receptors that respond to neural signals. When a motor neuron stimulates the muscle, the sarcolemma depolarizes and the electrical signal travels along its surface and into t-tubules, reaching the internal regions of the fiber. This electrical event triggers the sarcoplasmic reticulum to release calcium, which enables the interaction of actin and myosin to produce contraction.

Sarcoplasm is the cytoplasm inside the muscle fiber, not the membrane itself; myoglobin is the oxygen-binding protein within muscle cells; and the sarcoplasmic reticulum is the internal membrane network that stores and releases calcium during contraction.