Muscle Physiology and Contraction · USMLE Step 1

Which structural protein in muscle fibers contributes to elasticity and returns stretched sarcomeres to resting length after contraction or stretch?

  1. Actin
  2. Myosin
  3. Titin
  4. Tropomyosin
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Correct answer: Titin

Titin spans from the Z-disc to the M-line and acts as a molecular spring, contributing to the passive elasticity of muscle and restoring sarcomere length after stretch or contraction.

Difficulty: Medium Question 19 of 20

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