PARALYSERS OF MOTOR NERVES 85 



consequent stimulation, or separation by a half or a quarter 

 of a wave and consequent inhibition or restraint. 



ACTION OF DRUGS ON THE NERVES 



PARALYSERS STIMULANTS ELECTROTHERAPY 



Nerves may be acted upon in various parts of their course ; 

 in the nerve centres in which they originate ; in their cords 

 or trunks ; or in their minute endings distributed in muscles 

 or glands, or on the surface of the skin (sensory endings). 

 Motor nerves have their excitability more readily disturbed 

 or destroyed than sensory nerves. Injuries of compound 

 nerves frequently arrest motor function, but leave the 

 sensory function slightly, or only temporarily, impaired. 

 The nerve trunks are much less susceptible than the end 

 plates, and are only acted upon by strong solutions directly 

 applied to them. 



Nerve-endings motor, secretory, or sensory are acted 

 upon by many drugs, and these effects can be shown by 

 experiments on isolated organs. When an impulse is con- 

 veyed by a nerve to a nerve-ending, it is thought that some 

 chemical change takes place in the ending which produces 

 a substance acting on the cells of the muscle or gland to 

 cause either increased or decreased activity. Instead of an 

 impulse by way of its nerve fibres, the nerve-ending may be 

 acted upon in a similar fashion by various drugs applied 

 locally, or brought to it in the blood stream. 



Increased excitability of motor nerve-endings is produced 

 by aconitine, physostigmine, pilocarpine, and pyridine. 

 Alcohol, ether, and chloroform, applied directly to nerves, 

 first increase and then diminish their irritability. 



PARALYSERS of motor nerve-endings have their most 

 powerful representative in curare, which when injected 

 prevents stimulation of the nerve from producing a con- 

 traction. Numerous other agents act similarly, of which 

 the best known is conine. The nerve-endings in secretory 

 glands and unstriped muscle are also stimulated by drugs 

 like pilocarpine and physostigmine, whilst atropine and 

 hyoscyamine have the reverse effect. 



