What causes rigor mortis in muscle tissue?

Rigor mortis is caused by the lack of available ATP in muscle tissue after death. When a muscle cell is stimulated to contract, myosin heads attach to actin filaments to form cross-bridges, allowing muscle contraction to occur. This process requires ATP to release the attached actin and myosin molecules after the contraction has happened.

After death, ATP production ceases because there is no longer oxygen to facilitate cellular respiration or other energy-producing processes. As a result, the myosin heads remain bound to the actin filaments, leading to a state where muscles stiffen, which is rigor mortis. This phenomenon typically begins a few hours post-mortem and can last for 24 to 72 hours until the muscle proteins begin to break down.

The other options relate to various physiological processes but do not accurately describe the mechanism behind rigor mortis.