Muscle Physiology and Contraction · USMLE Step 1

Which statement about smooth muscle contraction is correct compared to skeletal muscle contraction?

  1. Smooth muscle completely lacks the proteins actin and myosin
  2. Smooth muscle uses a sliding-filament mechanism but with different regulation
  3. Smooth muscle can contract without requiring any ATP
  4. Smooth muscle is organized into sarcomeres with Z-discs
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Correct answer: Smooth muscle uses a sliding-filament mechanism but with different regulation

Smooth muscle contracts through a sliding-filament mechanism involving actin and myosin, but regulation differs (calcium-calmodulin, MLCK), and smooth muscle lacks sarcomeres/Z-discs.

Difficulty: Medium Question 14 of 20

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