NERVE 



61 



A. A neuron is usually stimulated from one or other of 

 its terminal dendritic endings, either by changes set up in 

 the tissues round these, or by changes in other neurons. 

 Thus (fig. 17) one set of neurons may be thrown into action 

 by changes in the tissue at their extremity, and a second set 

 may be stimulated by the activity of the first. 



B. Neurons may also be stimulated at any part of their 

 course, as may be demonstrated bv ])inchinQ- the ulnar nerve 

 behind the internal condyle of the luimerus, when a sensation 

 localised on the ulnar side of the hand is experienced, and 

 by the contraction produced in the gastrocnemius muscle of 



B 



Fig. 22. — A, To show a galvanic cell with a zinc and copper element and the 

 flow of the electric current passing round a galvanometer. B, A nerve 

 in which the dark part is in action and is acting to the rest of the 

 nerve as the zinc elements in the cell. 



the frog when the sciatic nerve is stimulated in its middle 

 (Practical Physiology). 



Means of Stimulation. 



kny sudden change tends to excite to activity, whether it be 

 mechanical, as in pinching a nerve, or a change in the 

 temperature, or in the electric conditions, or in the chemical 

 surroundings of the neurons ; agents wdiich withdraw water, 

 like glycerine, stimulating strongly. 



The electrical method of stimulating nerve is constantly 

 used in medicine, and it must be studied carefully. It is a 



