Why does rigor mortis occur after death?

• A. ATP production ceases, preventing muscle relaxation
• B. Enzymes rapidly break down muscle fibers
• C. Oxygen levels increase, causing muscle contraction
• D. Calcium ions accumulate in muscle cells, leading to sustained contraction

Answer: (D)

Verified step by step guidance

1. Understand the role of ATP in muscle contraction and relaxation: ATP is required to detach myosin heads from actin filaments during muscle relaxation. Without ATP, the myosin heads remain bound to actin, causing sustained contraction.
2. Learn about calcium ion regulation in muscle cells: Calcium ions are stored in the sarcoplasmic reticulum and released during muscle contraction. After death, calcium ions accumulate in the cytoplasm because the pumps that return calcium to the sarcoplasmic reticulum require ATP to function.
3. Recognize the cessation of ATP production after death: When an organism dies, cellular respiration stops, and ATP production ceases. This lack of ATP prevents the normal processes of muscle relaxation and calcium ion regulation.
4. Understand the biochemical basis of rigor mortis: The accumulation of calcium ions in muscle cells triggers sustained contraction, while the absence of ATP prevents the detachment of myosin from actin, leading to stiffness in the muscles.
5. Note the eventual resolution of rigor mortis: Over time, enzymes and other factors break down muscle proteins, causing the stiffness to subside as the body continues to decompose.