Enzyme histochemical and histographic data on normal human facial muscles.

Four human facial muscles, platysma, m. levator labii, zygomaticus major and orbicularis oris, obtained during head and neck surgery, revealed no qualitative differences from normal human limb muscles, but differences with regard to fiber type distribution and fiber size. Mean fiber diameters of each muscle studied were largely 50% of those encountered in normal human limb muscles. Histographic analysis revealed that type II fibers were more frequent than type I fibers but that type IIB fibers were extremely scarce in number. The myofiber diameter spectrum was also larger in facial than in limb muscles, as myofibers produced variability coefficients around 325. The frequent presence of intramuscular nerve twigs and motor endplates may provide the opportunity of studying pre- and postsynaptic pathology in future studies of denervated facial muscles.