Question

an action potential enters the depths of a muscle fiber by way of ________. multiple choice diffusion the t tubules voltage - gated ion channels the sarcoplasmic reticulum the neuromuscular junction

Explanation:

Action potentials enter the depths of a muscle fiber through T - tubules (transverse tubules). T - tubules are invaginations of the muscle cell membrane that allow the electrical signal to quickly reach the interior of the muscle fiber, triggering muscle contraction. Diffusion is too slow for rapid signal transmission in this context. Voltage - gated ion channels are involved in generating and propagating the action potential but not in its entry into the fiber's depths. The sarcoplasmic reticulum is involved in calcium storage and release related to contraction. The neuromuscular junction is where the nerve and muscle communicate, not the structure for action potential entry into the fiber's interior.

Answer:

B. the T tubules