PATHWAYS THROUGH THE SYMPATHETIC NERVOUS SYSTEM IN THE BULLFROG

Abstract

By dissection, reconstruction and recording of action potentials by means of the oscillograph a detailed analysis was made of the portion of the sympathetic nervous system of the bullfrog which arises from the first 6 nerve levels and includes the supply to the mesentery and gut. Nerve degeneration expts. were carried out upon the nerve roots, the rami and the sympathetic trunk. As a general pattern, with exceptions as noted, the "white" rami from a given level do not have synapses in the sympathetic ganglia of that level, but pass to ganglia at least one level above or below. There are typically 2 white ramus components, ascending and descending in the trunk from a given level. The splanchnic nerve is made up of rami from the 3rd to the 7th levels, the 5th contributing about half the total. Some of the splanchnic fibers arise from cells in the 4th to 7th sympathetic ganglia, some in the coeliac ganglion and some are pre-gangliomc past the coeliac plexus, the positions of the synapses of these fibers being very variable. The coeliac ganglion can be looked upon, therefore, as consisting of parts of the chain ganglia which have migrated further along the fiber pathways. A small white ramus at the 5th level can be traced into the dorsal root ganglion, does not degenerate after section of the roots, and its fibers have synapses in the 5th sympathetic ganglion. The larger white ramus at this level consists predominantly of fibers similarly originating in dorsal root ganglion cells. Most of these fibers course as far as the coeliac ganglion without synapses.