Physiology. 



Branched Processes 



Functions of the Spinal Cord. The spinal cord has two 

 main functions : 



i. Its conducting power, by means of the white fibers 

 which make up the outer part of the cord. These fibers 



may be regarded as connect- 

 ing the gray matter of the 

 brain with all parts of the 

 body. 



2. The gray matter is the 

 center of the reflex actions of 

 the cord. 



Ganglions. Masses of 

 nerve cells make up nerve 

 centers, or ganglions, such 

 as are on the dorsal roots of 

 the spinal nerves. These 

 also would show under the 

 microscope that their chief constituent is a collection of nerve 

 cells which give off one or more branches. The gray matter 

 of the spinal cord is considered a collection of ganglions. 



Reflex Action in a Sleeping Child. If the sole of the foot of a sleep- 

 ing child is gently tickled, the foot will be drawn up. The child has no 

 sensation. The brain has nothing to do with it. It is purely reflex 

 action. A nerve impulse has gone to the spinal cord, and another 

 impulse has been sent out to make the needed movement. But some- 

 times the child may be half awake and the foot might be drawn up by 

 voluntary action. Let us take another case, with which nearly every 

 one is familiar, to show that the brain has nothing to do with reflex 

 action. 



A Hen with its Head cut off. Nearly everybody knows that after a 

 hen's head is cut off, it "flops" around for some time, and that fre- 

 quently when one takes hold of its feet to pick it up, it begins to struggle. 

 Now this also is reflex action of the spinal cord. And there can be no 

 doubt that the brain has nothing whatever to do with it. 



Fig. 26. A Large Nerve Cell from the 

 Gray Matter of the Spinal Cord. 



