Which of the following describes the typical onset and progression of rigor mortis as per Nysten's law?

• A. Begins with the muscles of mastication and progresses head to feet
• B. Begins with leg muscles and progresses feet to head
• C. Begins with abdominal muscles and progresses torso outward
• D. No progression; all muscles stiffen simultaneously

Answer: (A)

Rigor mortis follows a head-to-toe progression. It typically starts in the muscles of the face, especially the jaw (muscles of mastication), and then the stiffness spreads downward toward the neck, trunk, and finally the limbs. This pattern happens because, after death, ATP runs out and calcium leaks into muscle fibers, allowing actin-mom cross-bridges to form and remain locked without ATP to detach them. Facial and neck muscles are often first affected due to their high metabolic activity and perfusion dynamics, so the stiffness moves from head to feet rather than from legs upward or appearing uniformly.