CVS Practice Test

Question: 1 / 400

What remains unchanged during sarcomere contraction?

I bands

A bands

The A bands remain unchanged during sarcomere contraction because they represent the length of the myosin filaments, which do not shorten when a muscle contracts. Instead, during contraction, the actin filaments slide over the myosin filaments, causing the I bands and H zone to decrease in size, while the overall length of the A band stays constant. This characteristic is essential for understanding how muscle contraction occurs at the microscopic level, as the sliding filament theory explains the mechanics behind muscle contraction involving the overlap of these protein filaments. The Z lines, which mark the boundaries of each sarcomere, also change position as the sarcomere shortens, further illustrating that it is the structures associated with the myosin, specifically the A band, that do not change in length during contraction.

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H zone

Z lines

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