Which mechanism activates smooth muscle contraction via calcium signaling?

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Study for the Anatomy and Physiology Muscular System Test. Prepare with flashcards and multiple choice questions; each question provides hints and explanations. Get ready to excel in your exam!

Multiple Choice

Which mechanism activates smooth muscle contraction via calcium signaling?

Explanation:
In smooth muscle, contraction is driven by calcium signaling that uses calmodulin rather than troponin. When calcium enters the cytosol, it binds to calmodulin, forming a Ca2+-calmodulin complex that activates myosin light chain kinase (MLCK). MLCK then phosphorylates the regulatory light chains of myosin, enabling myosin ATPase activity and allowing cross-bridge cycling with actin to produce contraction. Relaxation occurs when myosin light chain phosphatase removes those phosphates. The other ideas don’t fit: troponin C regulates skeletal (not smooth) muscle contraction; calcium does not directly bind to actin to enable contraction in smooth muscle; and calcium does not inhibit myosin ATPase.

In smooth muscle, contraction is driven by calcium signaling that uses calmodulin rather than troponin. When calcium enters the cytosol, it binds to calmodulin, forming a Ca2+-calmodulin complex that activates myosin light chain kinase (MLCK). MLCK then phosphorylates the regulatory light chains of myosin, enabling myosin ATPase activity and allowing cross-bridge cycling with actin to produce contraction. Relaxation occurs when myosin light chain phosphatase removes those phosphates. The other ideas don’t fit: troponin C regulates skeletal (not smooth) muscle contraction; calcium does not directly bind to actin to enable contraction in smooth muscle; and calcium does not inhibit myosin ATPase.

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