THE AUTONOMIC NERVOUS SYSTEM 531 



INHIBITION IN PERIPHERAL GANGLIA 



The existence of ganglion-cells in the course of the nerves to 

 visceral muscles has often been supposed to account for certain 

 peculiarities in the innervation of visceral, as compared with skeletal, 

 muscle. Chief among the differences between these two kinds of 

 muscle is the frequency with which inhibition may be brought about 

 in the latter by stimulation of peripheral efferent nerves. In skeletal 

 muscle inhibition is only known as the result of alteration of the 

 activity of the motor centres from which it is supplied. It has 

 therefore been thought that the peripheral ganglia of visceral muscle 

 play the part of the motor spinal centres of skeletal muscle, and 

 that when we excite an inhibitory nerve, say to the intestine, 

 we are interfering with and diminishing a tonic state of activity 

 which has its seat in a peripheral ganglion-cell connected with the 

 visceral muscle. 



This view, which was first put forward by Claude Bernard, has 

 been specially defended by Dastre and Morat. These observers point 

 out that vaso-dilator action diminishes or disappears as nerve-strands 

 are stimulated more and more peripherally, and conclude that the 

 vaso-dilator fibres run to the sympathetic ganglion and inhibit their 

 tonic action. The untenability of this view has been demonstrated 

 by Langley. Thus the chorda tympani fibres run to a local nerve - 

 ' centre ' in the hilum of the submaxillary gland. On Bernard's 

 theory stimulation of the fibres peripherally to the centre should cause 

 contraction of the arteries ; but it is found that, after paralysis of the 

 ganglion by nicotine, stimulation of the post-ganglionic fibres causes 

 dilatation, so that the nerve fibres given off from the local centre are 

 not vaso-constrictor but vaso-dilator. Moreover it can be shown that 

 the sympathetic fibres which do cause constriction make no connec- 

 tion with the cells in the hilum of the gland, but run on the walls of the 

 arteries to their distribution. These fibres are connected, not with 

 cells of the submaxillary ganglion (the local nerve-centre), but with 

 cells in the superior cervical ganglion. 



We must conclude that the inhibitory nerves in these visceral 

 structures exert their influence directly on the peripheral tissue, and 

 not by a diminution of activity of a tonically acting peripheral centre. 



AFFERENT FIBRES AND THE AUTONOMIC SYSTEM 



(REFERRED PAIN) 



The supply of afferent fibres to the viscera is very small in pjppor- 

 tion to the supply to the outer surfaces of the body. According to 

 Langley, in a visceral nerve, such as the hypogastric, only about one 

 tenth of the medullated fibres are afferent, and the proportion of 



