582 PHYSIOLOGY OF THE NERVE CELL AND THE SPINAL CORD 



8. CENTRAL FUNCTIONS OF PERIPHERAL NERVE CELLS 



In discussing the innervation of the heart, digestive organs, ureter, etc., 

 we have had occasion to mention the ganglion cells embedded in their muscu- 

 latures. According to some authors, as we have seen, it is to these ganglion 

 cells that the rhythmical contractions of these respective organs are due. 

 Others ascribe to the muscles themselves an automatic property in virtue of 

 which they are stimulated directly by the products of metabolism or by the 

 normal variations in pressure. 



We have no data as yet, except perhaps in the case of the intestine (cf. 

 page 288), which will enable us to reach a final decision as to the significance 

 of these ganglion cells. For this reason we shall limit the present discussion 

 to nerve cells in the 'sympathetic ganglia, in the spinal ganglia, and the 

 corresponding ganglia of the cranial nerves. 



The first question to engage our attention is whether the nerve fibers which 

 pass through the sympathetic ganglia actually form connections with the nerve 

 cells contained in them. 



Langley has shown that nicotine in not over-large doses stops the propa- 

 gation of impulses through the sympathetic ganglion cells, while it leaves 

 the nerve fibers and the peripheral nerve endings quite untouched; and he 

 has made extensive use of this fact in answering the question before us. It is 

 sufficient for the purpose merely to paint the ganglion with a solution of 

 nicotine. Then if stimulation of the nerve central to the ganglion has the 

 same effect as before application of the poison the nerve plainly does not 

 enter into connection with the contained nerve cells. But if the effect of 

 stimulation is nullified by the poison, we have evidence that the nerve cells 

 are intercalated in the conducting pathway. 



In this way Langley has found that every efferent nerve fiber or collateral 

 traversing the sympathetic pathways is connected with one peripheral ganglion 

 cell, and one only. This relay station, as we may call it, on the way from 

 the central system to the periphery may be situated either in a chain ganglion 

 or farther along toward the periphery, even as far as the vicinity of the 

 peripheral organ itself. The vasoconstrictor fibers, the secretory sweat fibers 

 and the pilomotor fibers of the fore paw (cat), all of which connect with the 

 first thoracic ganglion, may be mentioned as examples of fibers with the former 

 mode of connection. But most of the fibers of the splanchnic nerve end in 

 the ganglia of the solar plexus ; and the nerves of the external genital organs 

 likewise connect with nerve cells in the vicinity of the organs themselves 

 (cf. Chapter XXV). 



It is no easy matter to decide to what extent the nerve cells interpolated 

 in the course of the sympathetic nerve fibers have anything more than a 

 purely nutritive function. A priori the possibility is not to be denied that 

 these nerve cells, like those in the spinal cord, can exercise some central 

 functions, and certain observations which Goltz and Ewald have made on 

 dogs from which the greater part of the spinal cord from the lower cervical 

 or upper thoracic region backward had been removed, lend some support to 

 this view. 



