Specialized functional pathways are the building blocks of the autonomic nervous system.

The autonomic nervous system supplies each type of target organ via separate pathways which consist of sets of pre- and postganglionic neurones with distinct patterns of reflex activity. This has been firmly established for the lumbar sympathetic nervous system to skin, skeletal muscle and viscera, for the thoracic sympathetic outflow to the head and for several parasympathetic systems. In principle, that was already known by Langley. The specificity of the messages that these pathways transmit from the central nervous system arises from integration within precisely organized pathways in the neuraxis. The messages travel along discrete functional pathways and are transmitted to the target tissues via close neuroeffector junctions. Integration in the periphery occurs within each pathway, both in ganglia and at the level of the effector organs. We still need to understand how the central messages get through without distortion and how they control the diverse functions of the vasculature and viscera.