Smooth muscles are also called visceral muscles as they are present in the internal organs of the body, such as blood vessels, the gastrointestinal tract, the bladder or the uterus. These muscles are responsible for the contraction/movement of the internal organs. The smooth muscles are the weakest muscles and are controlled by the brain. The cell size of the smooth muscle is small. They greatly differ from the skeletal muscles as they are smooth, uniform and they have no striations.