Fig. 265 The 

 autoTiomic nerv- 

 ous system. Can 

 yon find plex- 

 uses? Where? 

 There are two 

 parallel chains 

 of ganglia like 

 the one shown 

 here. 



PROBLEM 2. Why Complex Behavior Is Vossible 279 



Evidently, the brain is not needed for 

 this reflex act. 



The autonomic nervous system. You 

 wull remember that the nervous system 

 is in two parts: the central and the auto- 

 nomic nervous system. The most impor- 

 tant fact about the autonomic system is 

 that it controls such bodily actions as 

 heartbeat, flow of digestive juices, secre- 

 tion from other glands, peristalsis, and 

 changing the size of arteries. The actions 

 the autonomic system controls are in- 

 voluntary. We do not decide on such 

 action. "We cannot, for instance, change 

 the rate of heartbeat or flow of gastric 

 juice at will. Notice that the autonomic 

 system controls glands, smooth or in- 

 voluntary muscle, and heart muscle; the 

 central nervous system controls striated 

 or voluntary muscle. 



The autonomic nervous system con- 

 sists of many nerves and ganglia. There 

 are two chains of ganglia near but out- 

 side the spinal column along the whole 

 length of the body cavity. These ganglia 



-''-'— '■'-'■- are connected to the nearby brain and 



apse not only to the eflrerent neuron but spinal cord by nerves. Near, or attached 

 also to another neuron whose axon ex- to, or within the walls of each of the or- 



tends all the way up through the cord to 

 the cerebrum. About the time the one 

 impulse reaches the muscle the other one 

 reaches a neuron in the cerebrum. You 

 become conscious of heat while you are 

 pulling your hand awa\^ 



A frog can be used to demonstrate that 

 a reflex goes through the spinal cord 

 without the use of the brain. By a simple 

 operation the brain of the frog can be 

 completely cut off from the cord. When 

 the skin on one side is irritated with acid, 

 the foot is raised and brushed against the 

 body just as it would be in a normal frog. 



gans controlled by the autonomic system 

 there are networks of nerves called plex- 

 uses. Such plexuses include ganglia as 

 well as nerves. 



The autonomic nervous system and 

 the central nervous system together con- 

 trol the activities of muscles and glands, 

 enabling them to work together. It is 

 because of this that the body acts as a 

 unit. 



Receptors are important. Although we 

 cannot see, hear, taste, smell, or feel with- 

 out the cortex of the brain, neither could 

 we do these things if we did not have 



