Forensic Medicine · Death & Postmortem Changes

Rigor Mortis & Cadaveric Spasm

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Rigor Mortis — Definition

Rigor mortis is the postmortem stiffening of muscles due to physicochemical changes occurring after death.

Mechanism

Normal muscle: ATP present → actin and myosin separate → muscle remains relaxed.

After death:

  1. ATP depletion
  2. Actin + myosin combine
  3. Actomyosin formation
  4. Muscle stiffening
  5. Rigor mortis

Nysten's Law (order of appearance)

Rigor mortis appears first in involuntary muscles and small muscles, then proceeds:

  1. Muscles of face
  2. Neck
  3. Upper limbs
  4. Trunk
  5. Lower limbs

It passes off in the same order in which it appears.

Time Course