Rigor mortis . is due to the loss of acetylcholine receptors at the neuromuscular junctions occurs as the sarcoplasmic reticulum deteriorates, releasing calcium ions is independent of environmental factors involves appendicular skeletal muscles only

Rigor mortis occurs as the sarcoplasmic reticulum deteriorates, releasing calcium ions.

Explanation:

Rigor mortis means stiffening of the body after death. It is one of the most significant signs of death, caused by a change in the chemical balance of the muscles after death. This is where the muscles become hard, making them difficult or impossible to move.

The biochemical cause of rigor mortis begins with the cessation of the pumping of calcium ions into the sarcoplasmic reticulum (due to the absence of ATP) so that the cytosolic concentration of this ion gradually increases, it also contributes to this increase in the cytosolic calcium ion concentration the degradation of the reticulum terminal cisterns. Blood circulation ceases, as does oxygen transport and withdrawal of metabolism products. Enzyme systems continue to function after some time of death. Thus, glycolysis continues in an anaerobic manner, generating lactic acid, which produces a lowering of the pH.

lysosome is this part of the cell is surrounded by a very thick outer membrane to protect the rest of the cell from its strong enzymes.