The activity in spinal preganglionic neurons is the result of the summation of potential changes in the neuronal membrane arising from integrative processes in the spinal cord, brain stem, hypothalamus and forebrain. As in the somatomotor system (Lloyd 1960), the spinal cord itself is a major highway of interaction between the brain and the autonomic target organs. In this chapter, I will concentrate on the thoracolumbar spinal autonomic (sympathetic) systems and summarize what is known and discussed about the sacral spinal autonomic (parasympathetic) systems. I will give arguments supporting the idea that the spinal cord contains intrinsic autonomic systems and that the spinal autonomic systems are coordinated via function-specific autonomic interneurons and integrated in the regulation of autonomic effector organs. This integration involves synaptic events derived from segmental spinal, propriospinal and supraspinal sources. Thus, I will put forward the idea that the spinal autonomic systems are integrated in the regulation of activity in preganglionic neurons by supraspinal centers. This idea has been borrowed from our understanding of the physiology of regulation of the activity in somatic motoneurons in the generation of movements. Alternative ideas discussed here are that spinal autonomic circuits modulate descending signals in the regulation of the activity in the preganglionic neurons or that spinal autonomic circuits are not important during normal regulation of autonomic target organs via sympathetic and sacral parasympathetic systems.

Sacral parasympathetic systems are essential in the regulation of lower urinary tract, hindgut and reproductive organs.