Teach PE points to bands of myosin and actin within the structural units of skeletal muscle as cause for the tissue's striated appearance. The units they are contained in are called sarcomeres, which are structurally distinct regions within individual muscle fibers.
PearsonHigherEd.com explains that each sarcomere is separated from its neighbors by Z lines, boundaries to which thin muscle filaments are attached. These thin filaments run from the Z line to which they are anchored toward the center of the sarcomere, but they do not run all the way to the Z line on the opposite side. Thick filaments rest within the center of the sarcomere and touch neither Z line. They partially overlap the thin filaments. The two regions on either end of the sarcomere that contain only thin filaments are called I bands, The region in the center with only thick filaments is called the H band and the region of overlap is called the A band. The University of Washington notes that the thick filaments are made up of myosin, while the thin filaments are composed of actin. These contrasting areas of myosin and actin produce the appearance of stripes. The University of Illinois at Chicago describes smooth muscle as having much shorter fibers and many more thin actin filaments than skeletal muscle, which results in smooth muscle's characteristic appearance.