NERVES 



267 



As a general rule, a large nerve accompanies an artery down the 

 inside of each limb and across the center of joints upon the side toward 

 which the limb is bent. Thus they are in protected positions. One 

 nerve cord is situated on the inside of the back of the elbow joint 

 and is called the funny bone. Owing to its unusual position, it is some- 

 times hit, producing a pain in its ending on the inside of the hand. 



479. Nerve action. When one of the main nerves of 

 the arm is irritated, as by a pinch or prick, or shock of 

 electricity, an impulse is started along the nerve in each 

 direction. It goes to the brain 

 and produces- a sensation either 

 of pain or pleasure. It also 

 goes to the muscle cells of the 

 arm, causing them to contract 

 and move the arm. If a nerve 

 is cut and the end nearest the 

 brain is irritated, a sensation 

 will be felt, but there will be 

 no motion. If the other cut 

 end is irritated, the muscles a nerve thread. 



Will move the arm, but no feel- b connective tissue binding the 



threads into a cord. 



mg whatever will be produced. 



Whether the nerve be irritated at its outer endings 

 at the cells or anywhere in its course, an influence will 

 travel to the central nerve cells carrying the news, and 

 also in the opposite direction to the cells of the body, 

 causing them to act. The cells of the body can originate 

 influences which travel up the nerve to the central nerve 

 cells ; and, on the other hand, the nerve cells can origi- 

 nate influences which travel to the cells of the body and 

 cause them to act. Transmitting impulses is the essential 

 duty of nerves. They may be compared to telephone 

 wires which transmit any kind of electrical influences over 



