Distribution of Sympathetic
The sympathetic system directly innervates most of the nutritive or vegetative system, the alimentary tract and its accessory organs, the vascular systems, the genito-urinary system, and the ductless glands. To a limited degree it shares this control with the cerebro-spinal and to a much greater degree it brings the central axis into indirect connection with these viscera.
Gray says, “The distinction of the sympathetic system from the cerebrospinal system is made merely for reasons of convenience. The two systems are intimately connected and the sympathetic is morphologically a derivative of the central axis disseminated in connection with the nutritive apparatus and establishing relationships among the vegetative organs.”
Structure of Nerve Pathways
Most pathways which carry nerve impulses from their origin or inception to the organ in which they are finally expressed as action of some sort or translated into sensation or into stimuli which pass out reflexly over a connected neuron, are composed of more than one neuron. The neurons of a nerve pathway are arranged end to end with the axons all pointing in one general direction so that the nerve energy travels always in the same direction over the entire nerve path. Impulses are transferred from the first neuron in the chain to the second, and from second to third, etc., by contact of the telodendria of the one neuron with the dendrites or receptive processes of the next. Part of the nerve pathway may be within the central axis and part within the trunk of a peripheral nerve.
Several peripheral pathways for afferent impulses may be joined to an efferent pathway so as to complete reflex arcs and the efferent cell be under the controlling influence of some upper neuron coming down from the central axis with the power either to permit or to inhibit the reflex acts which would otherwise take place as a result of peripheral stimuli. Several such lower cells may be under the domination of one upper neuron.
In some instances the nutrition of ganglia or nerve trunks, or of parts of the central axis itself, is under the control of sympathetic neurons terminating in connection therewith, so that interruption of the normal action of the sympathetic neuron may be followed by effects manifested through some distant part of the cerebrospinal system. In the following pages we shall discuss nerve pathways with reference to the explanation of diseases caused by vertebral subluxation impinging nerves either by tension or constriction, and therefore our grouping of parts will differ somewhat from any anatomical or physiological grouping with another object in view.
Important Nerve Pathways
To brain: C 2, 3, or 4 to superior cervical ganglion by direct impingement, through internal carotid nerve to sympathetic plexuses following branch arteries from Circle of Willis. The blood-supply of the brain is under control of the cervical sympathetic and most brain lesions or diseases are due to vascular changes leading to anaemia, hyperaemia, inflammation, or hemorrhage.
To meninges: Loop between first and second cervical nerves to trunk ganglion of vagus and through meningeal branches of vagus (P), or by way of internal carotid nerve to pial sympathetic plexuses. (P) The connection of the first, second, or third cervical with cerebral meningitis is established clinically but there is still doubt as to the explanation.