Question

part b (2 of 6)
2 tries left
excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. what specific event initiates the contraction?
sodium release from the sarcoplasmic reticulum initiates the contraction.
voltage - sensitive proteins change shape.
calcium release from the sarcoplasmic reticulum initiates the contraction.
action potentials propagate into the interior of the skeletal muscle fiber.

Explanation:

In skeletal - muscle contraction, the release of calcium ions from the sarcoplasmic reticulum is the key event that initiates contraction. Calcium binds to troponin, causing a conformational change that exposes the myosin - binding sites on actin, leading to cross - bridge formation and muscle contraction. Sodium is involved in the generation of the action potential but not the initiation of contraction at the level of the sarcomere. Voltage - sensitive proteins are involved in the coupling process but do not directly initiate contraction. Action potentials propagating into the muscle fiber are part of the excitation process but not the specific event that starts the contraction mechanism.

Answer:

C. Calcium release from the sarcoplasmic reticulum initiates the contraction.