One Nerve System
All nerve tissue in the body is organized and linked together in a complicated aggregation of individual units, communicating by contact, and forming one great Nerve System having its directing center in the Brain. It is said by some writers to consist of two distinct systems—cerebro-spinal and sympathetic—but would better be described as consisting of central organs—brain and spinal cord—and peripheral organs—cranial, spinal, and sympathetic peripheral axons connecting with cells in the central axis and linked together in a net-work improperly separable into separate or distinct divisions, the fibres of different parts being bound together in such a way as to establish an intricate intercommunication, closest on the one hand between the cranial and sympathetic and on the other between the spinal and sympathetic. The sympathetic system may be regarded as nothing more than a medium for proper distribution of impulses originating in the cerebro-spinal system, and a series of reflex centers deriving their power to act from the central axis. The proper action of sympathetic ganglia has been demonstrated to depend upon the integrity of the spinal nerve fibres, or rami communicantes, which pass to and terminate in the ganglia with their telodendria (terminal arborizations) in contact with the dendrites (cellulipetal processes) of the ganglion cells.
It will appear that interference with one division or part of the nerve system may be followed by effects partly manifested through a distant part; that excitation or inhibition of a spinal nerve may correspondingly excite or inhibit sympathetic fibres.