What structure distributes an action potential throughout the inside of a muscle fiber?

• A. Sarcoplasmic reticulum
• B. Motor end plate
• C. T-tubules
• D. Myofibrils

Answer: (C)

Verified step by step guidance

1. Begin by understanding the anatomy of a muscle fiber. Muscle fibers are composed of several structures, including the sarcoplasmic reticulum, motor end plate, T-tubules, and myofibrils.
2. Recognize the role of T-tubules in muscle contraction. T-tubules, or transverse tubules, are invaginations of the sarcolemma (muscle cell membrane) that penetrate into the cell's interior.
3. Learn how action potentials are transmitted. When a muscle fiber is stimulated, an action potential travels along the sarcolemma and enters the T-tubules.
4. Understand the function of T-tubules in distributing action potentials. The T-tubules ensure that the action potential reaches deep into the muscle fiber, allowing for a synchronized contraction.
5. Connect the role of T-tubules to muscle contraction. The action potential in the T-tubules triggers the release of calcium ions from the sarcoplasmic reticulum, leading to muscle contraction.