THE AUTONOMIC NERVOUS SYSTEM 



891) 



muscles of the bladder, the blood vessels of the rectum, and the internal 

 anal sphinctor. These fibers send collaterals to the bladder through 

 the hypogastric nerves. When one of these is cut and stimulated cen- 

 trally, the muscles innervated by the collaterals in the other hypogastric 

 nerve are seen to respond. There is no evidence, however, that this 

 mechanism is brought into play in normal life. 



The organs supplied by the autonomic nervous system appear to be 

 able to carry out their functions in an orderly way by virtue of their 

 inherent properties, of the presence of the primitive nerve network 

 which makes up their intrinsic nervous supply, and possibly by the assist- 

 ance of simple axon reflexes through the postganglionic fibers of the 

 thoracico-lumbar outflow. Since their reactions are simple and either 



Post, roof 

 gang.- 



Fig. 222. Diagram of an axon reflex in a sensory nerve fiber of the skin. A stimulus applied to 

 the skin is transmitted by the sensory fiber (N), part of it going to the spinal cord (SC), and 

 part of it passing by the collateral (C) to the arteriole (A), which it causes to dilate. 



strictly local or generally diffuse, a simple nervous mechanism suffices, 

 just as it does for the simple activities in the coelenterates (page 829). 

 Function of the Bulbo-sacral Division. The function of the connector 

 fibers in -the autonomic system would appear to consist largely in adjust- 

 ing the activities of these structures as a whole to the conditions of 

 activity brought about in the somatic musculature under the influence of 

 the central nervous system. Correlation takes place between visceral 

 activity, and somatic activity, so that the closest cooperation can ob- 

 tain between the organs of the body. This is brought out by considering 

 the way the three divisions of the autonomic system manifest themselves. 

 The bulbar outflow is concerned with conserving the resources of the 

 organism. Its action on the heart is to reduce its activity so that there 



