SYMPATHETIC NERVOUS SYSTEM. 



235 



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 belonging to the central nervous 

 system, whose axon emerges in one of the spinal 

 or cranial nerves and ends around the dendrites 

 of a sympathetic cell ; and one occurring in some 

 one of the numerous sympathetic ganglia, whose 

 axon passes to the peripheral tissue. The first 

 axon is spoken of as the preganglionic fiber, the 

 second as the postganglionic fiber. Their con- 

 nections are represented 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 



Prey any I ionic {lire. 



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Fig. 103. Schema to show the general relation between 

 the preganglionic and postganglionic fibers of the autonomic 

 paths. 



Fig. 104. Illus- 

 trating the central ori- 

 gin of the autonomic 

 fibers. (Langley.) 



