Straited muscle consists of hundreds of myofibrils packed into a regular parallel arrangement to form a muscle fibre. Striated muscle is given its name due to dark and light bands that can be seen down a light microscope when viewing myocytes. Striations are present in skeletal and cardiac muscle but not in smooth muscle. The bands that can be seen are fibers that have repeating sarcomeres. The dark bands (A bands) that can be seen are myosin filaments and are so named as they are anistropic. The light bands (I bands) that are observed are made up of actin filaments, and are so named because they are isotopic.