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nmdcat.online July 28, 2026

Concerning the mechanism of calcium binding during muscle contraction, a key distinction between visceral muscle and voluntary muscle is that visceral muscle:

A. Utilizes troponin C to initiate cross-bridge cycling
B. Relies on calmodulin to activate myosin light-chain kinase
✓
C. Sequesters all its calcium within the rough endoplasmic reticulum
D. Requires ATP for calcium binding rather than cross-bridge detachment

📝 Explanation

Visceral (smooth) muscle lacks the troponin complex found in skeletal (voluntary) and cardiac muscles. Instead, calcium binds to the regulatory protein calmodulin, which then activates myosin light-chain kinase (MLCK) to phosphorylate myosin and initiate contraction.

📖 Additional Information

  • Utilizes troponin C to initiate cross-bridge cycling
  • Relies on calmodulin to activate myosin light-chain kinase
  • Sequesters all its calcium within the rough endoplasmic reticulum
  • Requires ATP for calcium binding rather than cross-bridge detachment

Visceral (smooth) muscle lacks the troponin complex found in skeletal (voluntary) and cardiac muscles. Instead, calcium binds to the regulatory protein calmodulin, which then activates myosin light-chain kinase (MLCK) to phosphorylate myosin and initiate contraction.

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