Distribution of different fiber types in whole cross-sections of human platysma. A histological and morphometric study.

Analysis of cryostat cross-sections of the entire platysma muscle from human autopsies revealed enzyme histochemical and morphometric differences between normal human limb and facial muscles. The mean diameter of platysma fibers was about 50% of that of normal limb muscle fibers. Fiber type diameter increased from the medial to the lateral parts of the platysma. A variability coefficient of 356 indicated great variation in fiber caliber, with many fibers of 10 microns and less. Type I fibers showed an increase in density from the medial to the lateral parts of the muscle. The arrangement of histochemical fiber types was irregular with a tendency to form fiber type groupings.