Final answer:
Rigor mortis is the stiffening of the skeletal muscles after death due to the lack of ATP production, which prevents myosin heads from detaching from actin-binding sites, causing muscles to remain in a contracted state.
Step-by-step explanation:
The stiffening of the skeletal muscles after death is known as rigor mortis. This biological phenomenon occurs due to changes in the muscles' biochemistry. After death, the production of ATP (adenosine triphosphate) ceases because cellular respiration stops. ATP is necessary for the myosin heads in muscle fibers to detach from actin-binding sites after a contraction. When ATP is depleted, myosin heads remain bound to actin, preventing muscles from relaxing. This causes the muscles to become stiff, resulting in rigor mortis.
Rigor mortis is part of the post-mortem changes that occur in a body, and its onset and duration can be affected by several factors, including the ambient temperature and the physical condition of the deceased prior to death. It generally begins within 2 to 6 hours after death and can last up to 48 hours. As the body undergoes further decomposition, rigor mortis eventually dissipates.
Contrary to a living person experiencing muscle stiffness due to writer's cramp, which is caused by repetitive use of the muscles leading to temporary fatigue and lactic acid build-up, rigor mortis is irreversible until the decomposition processes further break down muscle tissues. As decomposition continues, the body eventually enters a stage called putrefaction, where tissues begin to break down and decompose due to the actions of bacteria and enzymes.