Final answer:
Livor mortis is caused by blood pooling in lower parts of a body after death and slows due to blood coagulation and loss of circulatory function. Myosin heads and actin-binding sites play a role in muscle movement during life, and their interactions after death lead to rigor mortis before eventual muscle breakdown.
Step-by-step explanation:
Livor mortis, or postmortem lividity, refers to the purple or reddish discoloration that appears on the lowermost parts of a cadaver, resulting from the pooling of blood due to gravity. It slows down and eventually stops due to the coagulation of the blood and loss of circulatory function postmortem. The relevant biological process during life is the attachment and detachment of myosin heads to actin-binding sites which result in muscle contraction or relaxation. When a person is alive, myosin heads rapidly detach from actin-binding sites causing muscle relaxation. An example of this is the temporary condition known as "writer's cramp". However, after death, the lack of ATP causes these heads to remain attached, leading to rigor mortis, where muscles stiffen. Eventually, the muscles will break down further due to chemical processes, resulting in the complete relaxation and fixating of the position of the body, including the livor mortis effect.