NERVE-ENDINGS. 



317 



a secondary neurone interposed. In the first case we have the 

 so-called reflex arc (Fig. 239, a, b}. The stimulus is carried 

 from the nerve-endings in the skin, through the cellulipetal 

 fibre, to the spinal ganglion cell. From here it is transmitted 

 through the dorsal root to the gray matter of the cord, where 



FIG. 239. 



Diagram showing the relations of sensory and motor neurones in the central nervous 

 system. The path of the impulse is indicated by arrows. (After Ramon y Cajal.) 



it is passed on to the dendrites of the motor neurone B, which 

 lies in the ventral horn. The stimulus then reaches the cell, 

 and is transmitted by means of the axone of that cell to the 

 motor nerve-ending in the muscle b. In this way refiex move- 

 merits take place. This relation is different when the stimulus 

 is transmitted to the cortex of the brain, and a voluntary move- 



