The term autonomic (autonomous, self-governing) nervous system was introduced to describe "the system of nerves which controls the unstriated tissue, the cardiac muscle and the glandular tissue of mammals." Originally, the term applied only to neurons with axons outside the central nervous system (CNS). More recently, the discovery that discrete neuronal groups in the brain stem, diencephalon, and cerebral cortex are involved in the control of autonomic function has broadened the definition of the ANS to include not only peripheral afferent and efferent pathways but also a complex network of neurons within the CNS.
The cell bodies of afferent autonomic (visceral) neurons are in the dorsal root ganglia of the spinal or cranial nerves and travel in both sympathetic and parasympathetic nerves toward the CNS (Fig. 21-1 (Figure Not Available) ). The autonomic CNS neurons are located at many levels from the cerebral cortex to the spinal cord. Efferent autonomic pathways are organized in two major outflows: the sympathetic and parasympathetic. Finally, the enteric nervous system, which is considered a separate and independent division of the autonomic nervous system, is located in the walls of the gut.
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