Which of the following changes occurs when skeletal muscles contract:
Correct answer: C. I-band shortens and Z-lines come close to each other
- A. I-band shortens only
- B. A-band shortens and Z-lines move apart
- C. I-band shortens and Z-lines come close to each other
- D. Actin filament contracts
Explanation
The I- band is the region near the Z - disc where we only have the actin filament. As the sarcomere contracts, the actin overlaps with the myosin filament, shortening the I band as well as bringing the Z discs closer to each other.
This question appeared on the UHS MDCAT 2017 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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According to the sliding filament theory, when muscle fibers are stimulated by the nervous system, which of the following changes occurs?
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