* 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. (MSH) * The part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands. (NCI) * those neurons which regulate the contraction of smooth and cardiac muscle and the secretion of glands, by way of the general visceral efferent component of cranial and spinal nerves; contains two divisions, parasympathetic and sympathetic which provide double innervation to most organs by way of a two-neuron chain, the first neuron has its cell of origin in the brain or spinal cord and the second in an autonomic ganglion. (CSP)