During the contraction of a skeletal muscle, which of the following does NOT change in length?
Correct answer: D. A band
- A. I band
- B. H zone
- C. Sarcomere
- D. A band
Explanation
The A band is the full length of the thick myosin filaments, and since the filaments themselves do not shorten, the A band stays the same width throughout contraction. The I band and the H zone both narrow because the thin filaments are pulled inwards over the thick ones, and the sarcomere as a whole therefore shortens. This constant A band is the strongest single piece of evidence for the sliding filament model.
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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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