210 



THE NERVOUS SYSTEM 



cotriiac 

 plexvcs 



' Solar 



plexus 



of the brain or spinal cord are known as ganglia. Neurons are 

 linked together by means of irregular projections of protoplasm, 



dendrites, establishing synapses. 

 The nature of these contacts is 

 not known. They may be com- 

 pared with contacts made by two 

 electrically charged wires. The 

 type of energy establishing the 

 contacts in a synapse is nervous 

 energy. 



Autonomic nervous system. 

 This system is also called the 

 sympathetic system or self-acting 

 system. In front of the spinal 

 cord, and lying parallel to it on 

 either side of the vertebral col- 

 umn, are two rows of ganglia, 

 connected with one another bv 

 nerve fibers. Certain large gan- 

 glia, called plexus, are also part 

 of this autonomic svstem. Three 

 of the plexus are the cardiac 

 plexus in the thoracic cavity, the 

 solar plexus in the abdominal 

 cavity, and the hj^^ogastric plexus 

 in the pelvic cavity, but they 

 connect with many other small ganglia in the thoracic and ab- 

 dominal regions. The autonomic system transmits some of the 

 disturbances of the central nervous system to the heart, glands, 

 and involuntary or plain muscles. Since the viscera (internal 

 organs) in general are made up of smooth muscle, it follows that 

 the so-called automatic mechanisms of the body, such as, the beat- 

 ing of the heart, the contraction and dilation of the muscles, and 



«.*• hypo- 

 plexus 



The autonomic nervous system consists 

 of a series of ganglia, most of which are 

 included in two chains that lie parallel to 

 the spinal column. These are connected 

 with nerve centers in the spinal cord. 



A very large and unpaired ganglion is 

 called a plexus. 



