Which area is most consistent with the initial onset of rigor mortis under Nysten's law?

Which area is most consistent with the initial onset of rigor mortis under Nysten's law?

• A. The muscles of mastication
• B. The leg muscles
• C. The back muscles
• D. The abdominal muscles

Answer: (A)

Rigor mortis under Nysten's law appears first in the muscles that had the most activity or the highest energy turnover during life, because they exhaust ATP quickly after death and the cross-bridges between actin and myosin lock in place when ATP is depleted. The muscles of mastication fit this pattern best: they are small but extremely active, consuming a lot of energy, and they are among the first muscles to run out of ATP after death. That combination makes them the first to stiffen, often making the jaw area the earliest region to show rigidity. In contrast, larger limb muscles such as those in the legs, back, or abdomen tend to stiffen later as rigor progresses from more active, energy-demanding groups to others.

Rigor mortis under Nysten's law appears first in the muscles that had the most activity or the highest energy turnover during life, because they exhaust ATP quickly after death and the cross-bridges between actin and myosin lock in place when ATP is depleted. The muscles of mastication fit this pattern best: they are small but extremely active, consuming a lot of energy, and they are among the first muscles to run out of ATP after death. That combination makes them the first to stiffen, often making the jaw area the earliest region to show rigidity. In contrast, larger limb muscles such as those in the legs, back, or abdomen tend to stiffen later as rigor progresses from more active, energy-demanding groups to others.