[Masticatory muscles. Part I. Functional anatomy of the masticatory muscles]

The anatomical design of the jaw-closing and jaw-opening muscles is of importance for their capability to produce forces and displacements. The length of the sarcomeres is a major determinant for both force and shortening range. The maximal work, force and shortening range each muscle is capable of producing, are proportional to the architectural parameters volume, physiological cross-sectional area and fiber length, respectively. Compared to the jaw openers, the jaw closers are characterized by shorter sarcomeres at the closed jaw, larger masses of contractile and tendinous tissue, larger physiological cross-sectional areas, shorter fibers and shorter moment arms. In addition, architectural features vary across the muscles of the same functional group and in some muscles significant intramuscular differences are found. In general, the jaw closing-muscles have architectural features that suit them for force production, whereas the jaw-opening muscles are better designed to produce velocity and displacement.