According to the sliding filament theory, a muscle shortens because
- A. actin filaments slide inwards over the myosin filaments
- B. both actin and myosin filaments themselves shorten
- C. the sarcomere is stretched by the load
- D. the Z lines dissolve and reform further apart
Explanation
Myosin heads bind actin, swivel, and drag the thin filaments towards the centre of the sarcomere, then detach and repeat, so the filaments overlap more without any of them changing length. The idea that the filaments contract is the older, wrong picture the theory replaced, and the unchanged A band disproves it. Each cycle of attachment and release needs one molecule of ATP.
Related questions
The functional contractile unit of a myofibril is the
During the contraction of a skeletal muscle, which of the following does NOT change in length?
Calcium ions start muscle contraction by binding to
Rigor mortis, the stiffening of muscles after death, occurs because
The neurotransmitter released at the neuromuscular junction of skeletal muscle is