During muscle contraction:
Correct answer: A. I-band shortens
- A. I-band shortens
- B. Myosin filaments shorten
- C. Actin filaments shorten
- D. Z-line disappears
Explanation
Option [A] During muscle contraction the following things happen:I band shortensZ lines come closerH zone disappearsHENCE option [A] is right.Option [B] is incorrect because myosin[thick] filaments do not shorten during contraction.Option [C] is incorrect because actin [thin] filaments do not shorten .Option [D] is incorrect because Z lines do not disappear but they just come closer together
This question appeared on the UHS MDCAT 2010 paper, which you can sit online with every answer explained.
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About Muscle Contraction
Muscle contraction is explained by the sliding filament model, in which myosin heads pull actin filaments within sarcomeres using ATP. The topic covers calcium, troponin, tropomyosin, the neuromuscular junction and relaxation, with attention to how filament length stays almost constant while the sarcomere shortens.
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