ABSTRACT
Organization of the Autonomic Nervous System The innervation of most tissues other than skeletal muscle is derived from the autonomic nervous system.1 The autonomic nervous system is comprised of millions of efferent pathways (neurons directed from the central nervous system to the tissues) and is divided into three divisions: sympathetic, parasympathetic, and enteric. The neurons of each division connect outside the CNS in cell clusters known as ganglia. Parasympathetic ganglia are located in the innervated organs whereas sympathetic ganglia are located closer to the spinal cord. The nerve fibers of the parasympathetic and sympathetic nervous system leave the CNS at different levels.2 Sympathetic neurons leave the CNS at the thoracic and lumbar spinal cord levels; accordingly, this division is also known as the thoracolumbar division. Parasympathetic neurons exit from different regions of the brain and sacrum; hence, this division is referred to as the craniosacral division.
