Skeletal muscle is the most abundant type of muscle tissue found in the  vertebrate body, making up at least 40% of its mass.  Although it is often activated by reflexes that function in automatically in response to an outside stimulus, skeletal muscle is also called voluntary muscle because it is the only type subject to conscious control.  Because skeletal muscle fibers have obvious bands called striations that can be observed under a microscope, it is also called striated muscle.  Note that skeletal muscle cells are multinucleate, that is, each cell has more than one nucleus.