232 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



Autonomic Nervous System. According to Langley, the 

 efferent fibers from the nerve cells of the sympathetic and re- 

 lated ganglia supply the plain muscle tissues, 

 the cardiac muscles, and the glands, that is, 

 the organs of the involuntary or, according to 

 an old nomenclature, the vegetative processes 

 of the body. He proposes for this entire sys- 

 tem of efferent fibers the term autonomic, to 

 indicate that they possess a certain independ- 

 ence of the central nervous system. The au- 

 tonomic system is contrasted physiologically 

 and anatomically with the efferent spinal and 

 cranial fibers that supply the striated or volun- 

 tary muscles: physiologically in the fact that 

 this latter group of fibers is entirely dependent 

 upon activities of the central nervous system, 

 and anatomically in the fact that the auto- 

 nomic fibers, although arising ultimately from 

 the central nervous system, all pass to their pe- 

 ripheral tissues by way of sympathetic nerve 

 cells. The autonomic path consists of two 

 neurons: one in the central nervous system 

 the axon of which emerges in one of the spinal 

 or cranial nerves and ends around the dendrites 

 of a sympathetic cell; and one, the axon from 

 the sympathetic cell which passes to the periph- 

 eral tissue. The first axon is spoken of as the 

 preganglionic fiber, the second as the post- 

 ganglionic fiber. Their connections are repre- 

 sented in the accompanying schema. (Fig. 103.) 



Physiological and anatomical investigations 

 have shown that autonomic nerve fibers arise 

 from four regions in the central nervous system 

 (Fig. 104) : First, from the midbrain, emerging 



oeuiolL 



* fore. 



nwsele. 



t 



Fig. 103. Schema to show the general relation between 

 :_ fit 



the preganglionic and postganglionic 

 paths. 



ibers of the autonomic 



Fig. 104. Illus- 

 trating the central ori- 

 gin of the autonomic 

 fibers. (Langley.) 



