The organization of lumbar preganglionic neurons.

The organization of pre- and postganglionic neurons supplying blood vessels of the skin (vasoconstrictor neurons) and of the skeletal muscle (vasoconstrictor neurons), sweat glands (sudomotor neurons) and erector pilimuscles (pilomotor neurons) of the cat's hind limb and tail is discussed. Each sympathetic subsystem has its own, though as yet unknown, central organization which is reflected in the reaction patterns typically seen. The conduction velocities of the pre- and postganglionic axons of each subsystem have their unique distributions. Postganglionic vasoconstrictor neurons supplying skeletal muscle and skin are influenced via cholinergic muscarinic and non-cholinergic synaptic mechanisms from thin, probably unmyelinated, preganglionic axons; postganglionic sudomotor and pilomotor neurons most likely do not receive this synaptic input. A high proportion of preganglionic neurons projecting with their axons onto postganglionic neurons which supply skin and skeletal muscle are silent and do not exhibit reflex activity. Some of these neurons synapse with postganglionic pilomotor, vasodilatator and sudomotor neurons; part of them may also synapse with vasoconstrictor neurons. However, the high proportion of preganglionic neurons without reflex and resting activity which cannot be classified on the basis of functional properties presents a considerable problem in the analysis of the central organization of the sympathetic nervous system. It is concluded that the 4 types of pre- and postganglionic neurons mentioned constitute 4 largely separate channels which transmit information from the spinal cord to the respective target organs.