Smooth muscle is typically comprised of numerous elongate spindle-shaped cells, each of which contains a single nucleus located in its center. As indicated by its name, the tissue displays no striations or other distinct patterns under the microscope. The contraction of smooth muscle is slow and generally under the control of the autonomic nervous system, resulting in its alternate moniker, involuntary muscle. Most of the body’s hollow internal organs, including all of the parts of the digestive system, are lined with smooth muscle.