324 ADVANCED PHYSIOLOGY 



SYMPATHETIC SYSTEM OF NERVES 



The term sympathetic system has been applied to a series 

 of nerve cells and fibres which connect all the spinal 

 nerves and, to a certain extent, bind them together, 

 not only anatomically, but to a limited extent in their 

 functional work also. Just how far there is any co- 

 operation of this kind is uncertain, and the term "sym- 

 pathetic," is not well applied. 



This system comprises two strands of nerve tissue lying in 

 the body cavity, one on each side of the back bone; Fig. 153. 

 Each line of fibres makes connections with each of the spinal 

 nerves on its side of the body, and at the junction with each 

 spinal nerve a ganglionic collection of nerve cells is formed. 

 Of course, no impulses really originate in the cords of the 

 sympathetic system, but the fibres in them take up impulses 

 which have come out over spinal nerves, from the spinal cord 

 or from the brain. 



The majority of branches from the sympathetic system go 

 to the blood vessels in the abdominal region, and exercise con- 

 strictor effects on them. Some go to the heart, others branch 

 and make an extensive network of fibres which here and 

 there fuse together forming, with the addition of nerve cells, 

 ganglia. Such ganglia are seen in the walls of the stomach, 

 in the body cavity, in the " small of the back " and also in 

 the neck, and from these ganglia, nerves pass out to near-by 

 organs. The secretion of some of the large glands like the 

 liver is controlled by impulses reaching them over the sym- 

 pathetic fibres. As a rule, the impulses which pass through 

 the sympathetic system are not under the control of the will, 

 and furthermore they generally provoke responses from the 

 organ to which they go of the very opposite character to that 

 produced by impulses over the ordinary spinal or cranial 

 nerves. For instance, the sympathetic nerves going to the 

 heart carry messages that stimulate it to more rapid action, 



