According to the sliding filament theory, when muscle fibers are stimulated by the nervous system, which of the following changes occurs?
Correct answer: A. I-bands shorten
- A. I-bands shorten
- B. H-zone becomes more visible
- C. Z-lines move further apart
- D. A-bands shorten
Explanation
According to the sliding filament theory, muscle contraction involves the sliding of thin actin filaments over thick myosin filaments within the sarcomere. This process brings the Z-lines closer together, shortening the sarcomere, and results in the shortening of the I-bands. The A-bands remain constant in length because they represent the region of overlap between actin and myosin. Conversely, the H-zone, which contains only myosin filaments, narrows or disappears entirely during contraction. Therefore, the correct answer is that the I-bands shorten during muscle contraction.
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