The Size and Distribution of Fiber Types in Jaw Muscles: a Review

Histochemical enzyme reactions and physiological recordings of limb and jaw muscles have independently revealed three to five types of muscle fibers. Surprisingly, type II fibers are smaller than type I fibers in major human jaw muscles. This is the opposite of the situation in limb muscles. Human jaw muscles contain mixed fiber types. Type I fibers predominate in lateral pterygoid and type II fibers in digastric muscles. The masseters in carnivorans and rodents contain mainly type II fibers, whereas those of some herbivorans, including rabbits and bovids, contain mainly type I fibers. Attempts were made to describe the functional significance of some observations.