Q.Explain why a dead body becomes stiff soon after death (rigor mortis).

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Without fresh ATP after death, myosin heads cannot detach from actin, so muscles stiffen (rigor mortis); the stiffness later passes as muscle proteins decompose. …

During normal muscle contraction, a myosin head detaches from actin only when a fresh molecule of ATP binds to it. After death, cellular respiration stops and no new ATP is generated anywhere in the body's muscle tissue. Whatever myosin heads happen to be cross-bridged to actin at that moment are therefore unable to complete the detachment step and remain permanently locked in place. Since this occurs simultaneously across countless sarcomeres in every skeletal muscle, the muscles as a whole become stiff and resistant to stretching -- the state of rigor mortis, which typically becomes apparent within a few hours of death. The stiffness eventually passes off, not because ATP becomes available again, but because the musc …

Trace what step of the cross-bridge cycle requires fresh ATP (detachment), then reason about what happens when th …

Assuming rigor mortis is permanent -- it is a temporary state that passes off once the muscle proteins themselves beg …