Read the following statements regarding the mechanism of muscle contraction: (a) Action potential in the sarcolemma causes the release of calcium ions from the sarcoplasmic reticulum. (b) Calcium ions bind to tropomyosin, exposing the active sites on the actin filaments. (c) The myosin head binds to the exposed active sites on actin to form a cross-bridge utilizing energy from ATP hydrolysis. (d) The cross-bridge pul

Step-by-step solution

Statement (a) is correct. An action potential travels along the sarcolemma and into the T-tubules, triggering the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm. Statement (b) is incorrect. Calcium ions bind to a subunit of troponin (not tropomyosin) on the actin filaments, which causes a conformational change that removes the masking of active sites for myosin. Statement (c) is correct. The myosin head, which has already hydrolyzed ATP into ADP and Pi, binds to the exposed active site