The peripheral autonomic nervous system supplies each group of target tissues by one (sometimes two) pathway(s) each consisting of sets of pre- and postganglionic neurons with distinct patterns of reflex activity as established for the lumbar sympathetic outflow to skin, skeletal muscle and viscera, for the thoracic sympathetic outflow to the head and neck and for some parasympathetic pathways. The principle of organization into functionally discrete pathways is the same in both the sympathetic and the parasympathetic nervous system, the only difference being that some functional targets of the sympathetic system are widely distributed (e.g., muscle blood vessels, skin blood vessels, sweat glands, etc.). Experimental investigations in humans support the idea of functionally discrete sympathetic pathways innervating skin or skeletal muscle developed in animal studies. The reflex patterns observed in each group of autonomic neurons are the result of integrative processes in the spinal cord, brain stem and hypothalamus. The concept that the sympathetic nervous system operates in an "all-or-none" fashion, without distinction between different effector organs, is not valid. The same applies to the idea of a functional antagonism between the sympathetic and parasympathetic nervous systems.

The spinal cord and brain stem are connected to the autonomic target cells by two-neuron chains of the peripheral sympathetic and parasympathetic nervous systems. These chains consist of populations of preganglionic neurons and postganglionic neurons that are synaptically connected in the autonomic ganglia. They transmit messages from the central nervous system to the target cells are called "final autonomic pathways." These pathways are the building blocks of the peripheral autonomic nervous system. The main difference between the final somatomotor pathways and the final autonomic pathways is that the central messages may undergo quantitative changes in the autonomic ganglia, and that some effector cells are innervated by more than one type of functional autonomic pathway. The impulse pattern transmitted by peripheral autonomic pathways to the target cells is the result of integration in the spinal cord, brain stem, hypothalamus and telencephalon. Reflex patterns that are generated by afferent stimuli in peripheral autonomic neurons may serve as physiological markers to analyze the functional structure of the autonomic circuits in the neuraxis. Using this approach of neurophysiological recording from single autonomic neurons in vivo, detailed knowledge has accumulated about the organization of the autonomic nervous system in animals and humans.