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nmdcat.online July 28, 2026

The physiological mechanism of contraction in smooth muscle involves the phosphorylation of myosin heads. The enzyme responsible for this phosphorylation is activated directly by:

A. ATP hydrolysis on the myosin head
B. The calcium-calmodulin complex
✓
C. The release of calcium from troponin
D. The binding of acetylcholine to motor end plates

📝 Explanation

In smooth muscle, calcium binds to calmodulin. The resulting calcium-calmodulin complex binds to and activates myosin light-chain kinase (MLCK), which then phosphorylates the myosin heads, allowing them to bind to actin and initiate contraction.

📖 Additional Information

  • ATP hydrolysis on the myosin head
  • The calcium-calmodulin complex
  • The release of calcium from troponin
  • The binding of acetylcholine to motor end plates

In smooth muscle, calcium binds to calmodulin. The resulting calcium-calmodulin complex binds to and activates myosin light-chain kinase (MLCK), which then phosphorylates the myosin heads, allowing them to bind to actin and initiate contraction.

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