Which muscle is typically the first to be affected by rigor mortis?

The first muscle typically affected by rigor mortis is the myoepithelial muscle, which is associated with the context of the question but is more generally referenced in discussions around muscle types. However, in human anatomy concerning rigor mortis, it is crucial to note that the muscles of the face and neck, particularly the small muscles, often exhibit rigor mortis before larger muscle groups.

Rigor mortis begins within a few hours after death and progresses through various muscle groups. Generally, it is observed that smaller muscles, such as those controlling facial expressions, are often among the first to show signs of rigidity. This is because they have a different fiber composition and require less ATP for relaxation compared to larger muscles like the quadriceps and hamstrings.

In this context, while 'myo' may refer to muscular components, it's important to understand which groups of muscles are primarily affected first in human postmortem changes, thus highlighting why 'myo' is the most relevant choice in this question. The other muscle groups, such as the trapezius, quadriceps, and hamstrings, are typically affected later in the progression of rigor mortis.