Rigor mortis, the stiffening of muscles after death, occurs because
Correct answer: B. ATP is no longer available to detach the myosin heads from actin
- A. calcium ions disappear from the sarcoplasm
- B. ATP is no longer available to detach the myosin heads from actin
- C. the muscle proteins are denatured by the fall in body temperature
- D. acetylcholine continues to be released at the neuromuscular junction
Explanation
ATP is needed not to form a cross bridge but to break one, so when respiration stops and ATP runs out the myosin heads stay locked on actin and the muscle cannot relax. Calcium in fact leaks out of the sarcoplasmic reticulum after death and floods the sarcoplasm, which is the opposite of the first option and is what allows the bridges to form in the first place.
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About Muscle Contraction
Muscle contraction is explained by the sliding filament model, in which myosin heads pull actin filaments within sarcomeres using ATP. The topic covers calcium, troponin, tropomyosin, the neuromuscular junction and relaxation, with attention to how filament length stays almost constant while the sarcomere shortens.
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