Autonomic Nervous System (ANS) is responsible for the vegetative functions of the body. It is composed of many ganglions, plexi, cerebrospinal nuclei and nerves. ANS, which is also known as visceral or vegetative nervous system, helps to control many functions, such as blood pressure, gastrointestinal motility, glands, bladder functions, sweating and body temperature. ANS innervates all the smooth muscles and the heart, and keeps to stabilize body functions within certain limits. ANS is composed of 3 components: sympathetic system (thoracolomber-adrenergic), parasympathetic system (craniosacral- cholinergic) and enteric system (nonadrenergic- noncholinergic). Autonomic nerves are classified with regard to their origin from central nervous system, the distribution of peripheral ganglions, their various physiological effects on visceral organs, and response to pharmacological agents. It is essential to know the anatomy and the physiology of the ANS, in order to evaluate disorders, achieve the correct diagnosis and to plan accurate treatment.