Rigor mortis typically becomes visible in which muscles first?

Explanation

## Onset and Progression of Rigor Mortis **Key Point:** Rigor mortis follows a predictable sequence of muscle involvement, beginning in smaller muscles and progressing to larger ones. ### Pattern of Spread **High-Yield:** The classic sequence is **downward and centripetal**: 1. **Eyelids** (first visible sign) 2. **Muscles of mastication** (jaw clenching) 3. **Neck muscles** 4. **Upper limb muscles** 5. **Trunk muscles** 6. **Lower limb muscles** (last to be affected) ### Timing and Duration | Feature | Details | |---------|----------| | **Onset** | 2–6 hours after death (average 4–6 hours) | | **Peak intensity** | 12–24 hours | | **Duration** | 24–48 hours; then gradually disappears | | **Disappearance order** | Same sequence as onset (eyelids first, lower limbs last) | **Clinical Pearl:** The eyelids and muscles of mastication are the earliest visible sites because they are small muscles with low ATP reserves. Larger muscles require more ATP and take longer to become rigid. ### Factors Affecting Onset - **Accelerated rigor** (1–2 hours): high ambient temperature, violent exercise before death, electrocution, tetanus - **Delayed rigor** (8–12 hours): cold environment, prolonged illness, cachexia **Mnemonic:** **EMUNT** — Eyelids, Mastication, Upper limbs, Neck, Trunk (then lower limbs) **Warning:** Rigor mortis is NOT present at the moment of death; it develops gradually over hours.