22O 



Life and Health 



c-- 



336. Motor and Sensory Nerves. After leaving the spinal 

 cord each nerve divides into minute branches which are 



distributed through the muscles 

 and terminate on the surface of 

 the body. 



The anterior roots become motor 

 nerves, their branches being dis- 

 tributed to certain muscles of the 

 body to control their movements. 



The posterior roots develop into 

 sensory nerves, their branches being 

 distributed through the skin and 

 Side View of the over the surface of the body to 

 become nerves of touch. 



In brief, the spinal nerves divide 

 and subdivide to reach with their 

 twigs all parts of the body and 

 connect every organ with the brain. 



The spinal nerves themselves are 

 merely conductors to carry messages 

 to and fro. They neither issue com- 

 mands nor feel a sensation. 



337. Functions of the Spinal Cord. The spinal cord is 

 the principal channel through which all impulses from the 

 trunk and extremities pass to the brain, and all impulses to 

 the trunk and extremities pass from the brain. That is, 

 the spinal cord receives from various parts of the body by 

 means of its sensory nerves certain impressions and con- 

 veys them to the brain, where they are interpreted. 



The cord also transmits by means of its motor nerves 

 the commands of the brain to the voluntary muscles and 

 so causes movement. Thus, when the cord is divided at 

 any point, compressed, as by a tumor or broken bone, or 



FIG. 120. 

 Spinal Cord. (Showing the 

 fissures and columns.) 



A, anterior median fissure; B, pos- 

 terior median fissure; C, ante- 

 rior lateral fissure ; D, posterior 

 lateral fissure ; , lateral col- 

 umn ; F, anterior column ; G, 

 posterior column ; H, posterior 

 median column; K, anterior 

 root; L, posterior root; M, 

 ganglion of N, a spinal nerve. 



