Multiple choice

How do muscle fibers contract?

  1. Thin filaments slide over thick filaments

  2. Thin filaments contract to become thick filaments

  3. Elastin proteins contract

  4. Elastins relax causing thick and thin fibers to contract
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A Correct answer
Explanation

According to the sliding filament theory, muscle contraction occurs when thin (actin) filaments slide past thick (myosin) filaments, pulling the Z-discs closer together and shortening the sarcomere. The individual filaments themselves do not shorten or change type.

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