There are two main components of the visceral and vascular walls, smooth muscle and nerves. The nerves in the visceral and vascular walls are mainly sympathetic and parasympathetic. Through the different actions of both, the smooth muscles in the visceral and vascular walls contract or relax, leading to contraction or relaxation of the visceral tubular organs and changes in the diameter of the blood vessels, thus achieving their different physiological functions. For example, when sympathetic nerves are excited, the viscera of the abdominal cavity and the terminal blood vessels contract, the smooth muscles of the bronchi dilate, gastrointestinal motility and gastric secretion are suppressed, and metabolism is hyperactive.