Chap. 16 CONDUCTION AND COORDINATION NERVOUS SYSTEM 



Table 16.2 

 Antagonistic Action in the Autonomic System 



297 



Sympathetic System 



The sympathetic nerves originating in the thoracic and lumbar regions 

 of the cord have a regulating influence on a great number of structures 

 (Table 16.2). The cell bodies of the first of two efferent neurons are located 

 in lateral regions of the gray matter of the cord and their axons extend out 

 through the ventral roots of the spinal nerves along with the axons of ordi- 

 nary motor cells (Fig. 16.14). After passing through a motor root the axons 

 of the sympathetic neurons separate from it and become the autonomic 

 branch of the spinal nerve leading to a vertebral sympathetic ganglion. 

 These ganglia contain the cell bodies of the second of the efferent neurons 

 whose axons go to the internal organs. They constitute a series of pairs 

 with one member on each side of the spinal cord (Fig. 16.15). 



Parasympathetic System. The parasympathetic group consists of nerves 

 with the first of their efferent neurons in the brain stem and the sacral region 

 of the spinal cord. Each vagus nerve which well earns its name arises from 

 the medulla, passes down the chest and abdomen, and mainly innervates the 

 heart, respiratory system, and the digestive system as far as the large in- 

 testine. 



The peripheral ganglia, containing the second of the efferent neurons of 

 the parasympathetic nerves, are usually near or in the organs innervated. 

 These as well as the vertebral ganglia of the sympathetic nerves are the loca- 

 tions of synaptic connections outside the central nervous system. This is a 

 unique characteristic of the autonomic nervous system. 



