The autonomic nervous system consists of the sympathetic and parasympathetic systems, which control many functions in the body such as blood flow, sweating, secretion from glands, etc. The sympathetic nervous system is also involved in pain generation in some conditions such as complex regional pain syndromes. Injecting local anesthetic on the sympathetic ganglia in different areas of the body can relieve pain, improve blood flow to the arms or legs and intestines, reduce sweating, etc.