The enteric, parasympathetic, and sympathetic nervous systems taken together. Generally speaking, the autonomic nervous system regulates the internal environment during both peaceful activity and physical or emotional stress. Autonomic activity is controlled and integrated by the central nervous system, especially the hypothalamus and the solitary nucleus, which receive information relayed from VISCERAL AFFERENTS; these and related central and sensory structures are sometimes (but not here) considered to be part of the autonomic nervous system itself.