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Sliding Filament Theory
Concepts tested here
- Band changes during contraction
All Questions
2001 AIPMT 1 question
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Which statement is correct for muscle contraction : -
More than one option is correct.
According to the sliding filament theory, during contraction the thin (actin) filaments slide over the thick (myosin) filaments towards the centre of the sarcomere. The filaments themselves do not shorten.
The A-band equals the length of the thick filaments, so it remains constant.
The H-zone (part of the A-band without overlap) decreases, and may disappear.
The I-band decreases, and the Z-lines come closer, so the sarcomere shortens.
So both 'the length of the H-zone decreases' and 'the length of the A-band remains constant' are correct.
Note: the answer key of the source accepts both of these statements, so both are marked correct here.