Which structure is last to appear in the order of appearance for rigor mortis?

Which structure is last to appear in the order of appearance for rigor mortis?

• A. Lower extremities
• B. Upper extremities
• C. Jaws
• D. Face and neck muscles

Answer: (A)

Rigor mortis occurs when ATP is no longer available to detach the myosin heads from actin, so muscles lock in a stiff position after death. The timing and order depend on how quickly ATP is depleted and how muscle mass and location influence the diffusion of changes. The small muscles of the face and jaw are typically the first to stiffen because they have a small mass and reach the critical conditions for rigor sooner. The stiffness then spreads to other muscles, usually progressing to the neck and then the upper limbs. The large, deeper muscles of the lower extremities take longer to reach that threshold, so they are the last to become rigid. Temperature also affects the speed—warmer conditions speed up onset, cooler conditions slow it down. Therefore, the structure that is last to appear is the lower extremities.

Rigor mortis occurs when ATP is no longer available to detach the myosin heads from actin, so muscles lock in a stiff position after death. The timing and order depend on how quickly ATP is depleted and how muscle mass and location influence the diffusion of changes. The small muscles of the face and jaw are typically the first to stiffen because they have a small mass and reach the critical conditions for rigor sooner. The stiffness then spreads to other muscles, usually progressing to the neck and then the upper limbs. The large, deeper muscles of the lower extremities take longer to reach that threshold, so they are the last to become rigid. Temperature also affects the speed—warmer conditions speed up onset, cooler conditions slow it down. Therefore, the structure that is last to appear is the lower extremities.