Forensic Pathology Rigor Mortis Rigor Mortis Rigor Mortis

Forensic Pathology - Rigor Mortis

Rigor Mortis

Rigor Mortis Is the period of time that a body goes through a state of Rigidity • ATP is required for muscle contraction and relaxation • Ca+ ions are required for muscle contraction and prevent muscle relaxation. • Aerobic respiration needs O 2 to make ATP • The Phosphagen system and Anaerobic respiration can make small amounts of ATP rather quickly without O 2

Rigor Mortis • When the body dies aerobic respiration no longer occurs – No large production of ATP • The Phosphagen system and Anaerobic respiration produce small amounts of ATP while muscle stores of creatine and glycogen last • Low levels of ATP – Causes the Ca+ ions to be dumped in to the muscle fibers from their vesicles. – Ca+ ions and ATP produced from the phosphagen system and anaerobic respiration produce a muscle contraction.

Rigor Mortis • The ATP produced from the Creatine phosphate system and anaerobic respiration can not be used to relax the muscles because the Ca+ ions can not be drawn out of the muscle fibers – The muscles ratchet to a full contraction • Lactic Acid is a by product of anaerobic respiration – O 2 is required to remove Lactic acid – As p. H drops (acidic) proteins in the muscle denature and the contraction degrades.

Rigor Mortis Progression • Shorter muscles – face, fingers, toes

– Neck

– Then moves down and out the long muscles of the legs and forearms

– Legs stiffen last

Rigor Mortis Time-line • 1 -4 hours: Jaw and neck rigid, rest of body limp • Up to 8 hours: everything down to the legs is rigid • For 12 hours: everything remains rigid • 24 hours: Jaw is limp, everything else is rigid • 30 -32 hours: everything but the legs are limp • 36 hours: entire body is limp (no rigidity) decomposition has begun

Factors Affecting Rigor Mortis Factor Temperature Activity Before Death Event Effect Circumstances Cold Temperature Inhibits Rigor slower onset & progression Warm Temperature Accelerates Rigor faster onset & progression Accelerates Rigor lack of oxygen to muscle & higher body temp accelerates rigor Sleep Slows rigor muscles fully oxygenated will exhibit rigor more slowly Obese Slows rigor fat stores oxygen Thin accelerates rigor body loses oxygen quickly and body heats faster Aerobic exercise Sleep Body weight

Rigor Mortis to estimate time of death Body warm not stiff less than 3 hours ______hrs Body warm stiff 3 -8 hours ______hrs Body cool stiff ______hrs 8 -36 hours Body cool not stiff ______hrs more than 36 hours