COORDINATION AND CONTROL: (1) THE NERVOUS SYSTEM 



119 



of each autonomic trunk, and the two trunks join in a common ganglion 

 in the lower abdomen. 



These autonomic trunks and ganglia provide pathways and connections 

 for reflexes that are semi-independent of the central nervous system. 

 Nerve fibers from the ramus communicans enter the autonomic ganglia 

 and either make synapses with neurons that lie wholly in the autonomic 

 division or pass along the autonomic tracts to various visceral receptors. 

 Apparently all efferent impulses that reach the viscera from the central 



Fig. 7.8. A stereogram to show some of the relations between the central and autonomic 

 nervous systems. The rectangular insets show details of receptors, the circular insets show 

 effector endings. The cord is sectioned at the level of a pair of spinal nerves. Note that each 

 autonomic trunk bears a ganglion at this level. 



nervous system must traverse at least two efferent neurons, a preganglionic 

 neuron, the body of which lies in the central nervous system, and a post- 

 ganglionic neuron, which lies wholly within the autonomic system and 

 relays the impulse to the effector. In addition, many purely autonomic 

 neurons make direct connections between the various ganglia of the 

 paired autonomic trunks; other autonomic fibers connect the trunk 

 ganglia with other and special autonomic ganglia that lie deep within 

 the viscera. 



In spite of its name, the autonomic system is not independent but is 

 closely tied to and acts in intimate relation with the central nervous 

 system. Two distinct functional divisions of the autonomic system are 



