Striated muscle is connected directly to the central nervous system and is under the control of the will. In most cases it is attached to the skeleton. The muscle fibers are much larger than those of smooth muscle. An individual fiber may be from l to 40 mm long and l0 to l00 µm in diameter, the size of a piece of thread so that many are visible with the naked eye. This large cell is a syncytium, a multinucleate mass of cytoplasm enclosed within a single cell membrane. There are approximately 35 nuclei per millimeter of length.