myofilament /mī′ōfil′ə·mənt/ [Gk, mys, L, filare, to spin] , any of the numerous ultramicroscopic threadlike structures occurring in bundles in the myofibrils of striated muscle fibers. The thick filaments of myosin and the thin filaments of actin are together responsible for the contractile properties of muscle. Also present are intermediate filaments, of uncertain function. See also myofibril, actin, myosin.
