Sympathetic preganglionic neurons are located in the intermediate zone of the thoraco-lumbar spinal cord, those supplying somatic tissues being located laterally in the intermediolateral nucleus and those supplying viscera more medially. Sacral parasympathetic preganglionic neurons are located in the sacral intermediate zone. Parasympathetic preganglionic neurons in the brain stem are located in special nuclei. The nucleus tractus solitarii (NTS) receives peripheral synaptic input from gustatory afferents (rostral half) and from gastrointestinal, respiratory and cardiovascular afferents (caudal half). The NTS neurons project to nuclei in the brain stem, hypothalamus and forebrain, and receive synaptic input from these brain sites. Several groups of autonomic interneurons lie in the thoracolumbar and sacral spinal cord. Sympathetic premotor neurons that project to the preganglionic neurons are situated in the ventrolateral medulla, ventromedial medulla, caudal raphe nuclei, A5 area, medial hypothalamus and lateral hypothalamus. Parasympathetic premotor neurons that project to preganglionic neurons innervating heart, pancreas, trachea or salivary glands are located in the ventral medulla in the same nuclei as sympathetic premotor neurons but additionally in the periaqueductal gray. Neurons antecedent to autonomic premotor neurons are also present in various nuclei of the pons, periaqueductal gray, hypothalamic nuclei and nuclei of the telencephalon.