THE CENTRAL NERVOUS SYSTEM 371 



to the muscles are still intact. Only the rpinnl 

 cord has been destroyed. 



The conversion of sensory into motor impulses 

 for skeletal muscles is a function of the central 

 nervous system. 



Influence of Afferent Impulses on Reflex Action. 

 Destroy the brain of a strong frog with the seeker. 

 Gently pinch a toe of the right foot. 



Only the right leg will be drawn up. 



Pinch a toe of the left foot. 



Only the left foot will be drawn up. 



Pinch a finger. 



Only the corresponding arm will move. 



Pinch the whole foot sharply. 



More extended movements will be made. 



The character and location of the stimulus 

 affect the resulting c;>:ilra :ti >n. 



Threshold Value Lower in End Organ than in 

 Nerve-Trunk. '1. Carefully expose the sciatic 

 nerve. Determine the least strength oi tetanizing 

 current that will cause a crossed reflex when 

 applied to the skin of the foot. Now apply the 

 same stimulus to the trunk of the nerve. 



As a rule, the intensity required to produce 

 reflex action is less when the stimulus is applied 

 to the peripheral endings of the sensory nerves 

 than when the nerve-trunks are stimnlnred. 



