When a muscle fibre shortens, the following also shortens:
Correct answer: B. Sarcomere
- A. Actin filament
- B. Sarcomere
- C. Both Options A and B are correct
- D. Myosin
Explanation
Option A: Actin filament alone does not shorten during muscle contraction. Rather, the actin filaments slide over the myosin filaments, causing the sarcomere to shorten. Option B: For a muscle cell to contract, the sarcomere must shorten. However, with thick and thin filaments, the components of sarcomeres do not shorten. The A band stays the same width and, at full contraction, the thin filaments overlap. When a sarcomere shortens, some regions shorten whereas others stay the same length. Option C: As explained above this is an incorrect option. Option D: Myosin filament alone does not shorten during muscle contraction. Rather, the myosin filaments slide over the actin filaments, causing the sarcomere to shorten.
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About Support and Movement
Support and movement covers the axial and appendicular skeleton, bone structure, joints and the arrangement of skeletal muscles. Muscle contraction is explained through actin, myosin, sliding filaments, calcium ions and ATP, while arthritis is distinguished as a disorder of joints rather than a normal part of movement.
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