Smooth muscle contraction
In smooth muscle, Ca2+ starts contraction by binding:
Answer C: explanation for every choice
A
Troponin C is the Ca2+ sensor in skeletal and cardiac muscle. Smooth muscle lacks troponin.
B
Tropomyosin doesn't bind Ca2+.
C
Correct. Ca2+–calmodulin activates myosin light-chain kinase, and phosphorylation of myosin enables cross-bridge cycling.
D
Actin doesn't serve as the Ca2+ sensor.
TakeawaySkeletal and cardiac: Ca2+–troponin. Smooth: Ca2+–calmodulin–MLCK.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb174.