Rigor mortis is caused due to

Options

A. Breakdown of cross-bridges between actins and myosins
B. Lack of ATP and phosphocreatine
C. Sustained cross bridges between actins and myosins
D. Both (2) & (3)

Answer

**Step-by-Step Solution:**

1. **Understanding Rigor Mortis**: Rigor mortis is a postmortem change that occurs after death, characterized by the stiffening of the muscles in the body. This change is important for forensic science as it can help determine the time of death.

2. **Chemical Changes in Myofibrils**: The stiffening of muscles is due to chemical changes occurring in the myofibrils, which are the contractile units of muscle fibers. After death, the body ceases to produce ATP (adenosine triphosphate), which is essential for muscle relaxation.

3. **Role of ATP**: ATP is necessary for the detachment of myosin heads from actin filaments during muscle contraction. When the body dies, ATP production stops, leading to a lack of ATP in the muscle cells.

4. **Sustained Cross Bridges**: In the absence of ATP, the myosin heads remain attached to the actin filaments, resulting in sustained cross bridges. This state of attachment causes the muscles to become rigid, leading to rigor mortis.

5. **Elimination of Incorrect Options**:
- Option 1 states the breakdown of cross bridges between actin and myosin, which is incorrect because rigor mortis is caused by the sustained cross bridges, not their breakdown.
- Options 2 and 3 correctly identify the lack of ATP and the sustained cross bridges as causes of rigor mortis.
- Therefore, option 4, which states that both options 2 and 3 are correct, is the right answer.

**Final Answer**: Rigor mortis is caused due to the lack of ATP and sustained cross bridges between actin and myosin (Option 4).

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