THE NERVOUS SYSTEM 



297 



that runs down in front of the backbone, all connected by 

 nerves. The nerves of the system form several intricate 

 networks, each 'called a plexus 

 (Fig. 200). The largest and 

 most important is the solar 

 plexus, just behind the stom- 

 ach; its nerves supply the 

 muscular walls of the abdomi- 

 nal organs. Another plexus is 

 found in connection with the 

 heart. 



550. Sensory Nerves of the 

 Sympathetic System. - - The 

 sensory impulses through these 

 nerves are slow and faint, sel- 

 dom reaching beyond the spinal 

 ganglia to the brain. Thus 

 the circulation of the blood 

 and the digestion of the food 

 usually go on without our con- 

 sciousness, but a very strong 

 irritation may give rise to con- 

 sciousness and pain in the 

 abdominal organs, as in colic 

 or in vomiting. Sensory im- 

 pulses, signifying the needs of 



the cells and the necessitv for FIG. 200. - Diagram of Trunk show- 

 in? One of the Two Rows of Svmoa- 



movement in the arteries and 

 intestines, are being continu- 

 ally sent to the spinal ganglia. 

 Only very strong impulses 

 caused by disturbances that may injure the body, reach 

 the brain, and cause pain. 



551. Motor Sympathetic Nerves. The motor nerves 

 carry impulses which cause the epithelial cells of the 



ing One of the Two Rows of Sympa- 

 thetic Ganglia near the Spinal 

 Column and the Plexuses. 



i, cardiac plexus; 2, solar plexus; 3, hy- 

 pogastric plexus; 4, 5, 6, 7, row of 

 ganglia near spinal column. 



