206 The Vertebrate Organ Systems 



The Autonomic Nervous System. — Anatomically the autonomic 

 nervous system is actually part of the peripheral nervous system; func- 

 tionally, however, it is quite distinct. Its function is that of controlling 

 the activities of the glands, smooth muscle movements, and the heart 

 rate. In other words, it controls the unconscious automatic activities 

 of the visceral organs. This control is a double one, that is, some of 

 the fibers of this system excite, others inhibit, resulting in an elaborate 

 system which assures proper functioning. In the discussion of the rate 

 of the heartbeat this double innervation was particularly emphasized. 

 Such control is equally important in all the other visceral organs. 



DILATION. 



/^ ~uiii^ \«_CONSTniCTION 



SYMPATHETIC X sauvarv^^x^ \ rara- 



r-\v»s<>\ SYMPATHETIC 



SACBAL 

 COBD 



Fig. 64. — Diagram of the autonomic nervous system. 



The autonomic system thus consists of two distinct sets of fibers 

 which have different origins (Fig. 64). Most of the one set of fibers 

 originate from a series of ganglia which lie ventral and lateral to the 

 spinal cord and outside the spinal column. These ganglia, by means 

 of synaptic connections, are closely associated with both the motor 

 and sensory portions of the spinal nerves. Collectively, these ganglia 

 and their nerve processes are known as the sympathetic division of 



