Specificity in the organization of the autonomic nervous system: a basis for precise neural regulation of homeostatic and protective body functions.

Experimental investigations of the lumbar sympathetic outflow to skin, skeletal muscle and viscera and the thoracic sympathetic outflow to the head and neck have shown that each target organ and tissue is supplied by one or two separate pathways which consists of sets of pre- and postganglionic neurons with distinct patterns of reflex activity. This probably applies to all sympathetic and parasympathetic systems. The specificity of the messages that these peripheral pathways transmit from the central nervous system arises from integration within precisely organized pathways in the neuraxis. The messages in these discrete functional pathways are transmitted to the target tissues often via organized neuroeffector junctions. Modulation in the periphery can occur within each pathway, both in ganglia and at the level of the effector organs. This organization is the basis not only for precise neural regulations of all homeostatic body functions in which the autonomic nervous system is involved but also the basis of one main component in the regulation of protective body functions: (a) Elementary defense behaviors which are organized in the mesencephalon (confrontational defense, flight, quiescence), (b) regulation of the immune system by the sympathetic nervous system, and (c) adaptive autonomic motor responses during basic emotions require precisely working autonomic, in particular sympathetic, systems. In this sense, the concept of the functioning of the sympathetic nervous system in an "all-or-none" fashion, without distinction between different effector organs, and of simple functional antagonistic organization between sympathetic and parasympathetic nervous system is misleading, inadequate and untenable.