THE N EURO-MUSCULAR JUNCTION 263 



end-plate. The latter therefore forms an anatomical break 

 in the neuro-muscular mechanism. This break has a definite 

 physiological significance, for it possesses certain special 

 properties on account of which the nature of the impulse 

 passing along it differs from an impulse passing along a 

 nerve-fibre. (1) There is evidence to show that the end- 

 plate is more liable to fatigue than the nerve-trunk; 

 (2) there is a delay in the transmission of the impulse 

 across it; (3) impulses traverse it in one direction only — 

 from nerve to muscle ; (4) it responds to stimuh of extremely 

 short duration ; (5) it is pecuharly susceptible to the action 

 of drugs. 



It is therefore beheved that between the nerve-ending 

 and the muscle-fibre a third substance exists differing 

 physiologically both from nerve and from muscle. This 

 substance forms a structure called the neuro-muscular 

 junction. 



