The given diagram shows two relaxed sarcomeres I and II from skeletal muscle.The effect of contraction of sarcomeres I and II on the A-band is that it will
Correct answer: D. Not change in size
- A. Disappear
- B. Reduce in size
- C. Lengthen in size
- D. Not change in size
Explanation
The A-band in a sarcomere corresponds to the length of the thick myosin filaments. During muscle contraction, the sarcomere shortens, but the length of the thick filaments remains the same. Therefore, the A-band does not change in size. The other options are incorrect because they suggest changes to the A-band that do not occur during contraction. The A-band does not disappear, reduce, or lengthen; it remains constant.
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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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