202 HANDBOOK OF PHYSIOLOGY ^ NELfROPHYSIOLOG\' I 



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FIG. 1. Surface view of neuromuscular junction of lizarcl stained with Janus green. The only 

 parts to have taken up the stain are the regions of muscle bordering the ner\e terminals (the sub- 

 neural apparatus) and a short piece of nerve at the termination of the myelin. The final part of 

 the myelinated nerve fiber appears in the extreme left of the upper picture. In the lower picture a 

 portion of the junction is shown at higher magnification revealing the lines in the subneural appara- 

 tus, which are oriented at right angles to the edge of the nerve and which are uniformly spaced 

 about 0.4 M apart. [From Couteau.x (15).] 



FIG. 2. Electronmicrograph of lizard neuromuscular junction. Two nerve terminal branches are 

 seen in the left side of the main picture with the muscle to the right. The dark oval bodies in the 

 nerve and muscle are mitochondria. The surface of the muscle at the junction is thrown into a 

 series of folds, which correspond in their repetition interval and depth to the lines in hg. i . From 

 the appearance where the surface membrane of the nerve can be clearly seen, it is established that 

 it does not enter the folds. The inset gives an enlarged view of the situation at the junction. The 

 surface membranes of nerve and muscle probably correspond to the two dense lines separated by 

 about 0.07 fi. [From Robertson (71)] 



about 0.05 /i and their depth about 0.5 ^l. This in- 

 folding considerably increases the area of postjunc- 

 tional membrane which may have an important 

 bearing on the magnitude of the alteration produced 

 in the junctional region during transmission. The 

 teloglia does not occur within the grooves but appears 

 to remain in contact with the exposed part of the nerve 

 cylinder. This suggests that it plays no direct role in 

 the transmission process. 



LOCAL ELECTRICAL RESPONSE 



The study of neuromuscular transmission received 

 a great impetus with the application of electrical 

 recording techniques to the junctional region. It 

 was observed by a number of workers that after a 

 muscle had been treated with just sufficient curare to 



prevent contraction from nerve stimulation, there 

 still occurred an electrical change in the muscle, 

 though this was different from the action potential 

 type of response (13, 30, 33, 43, 45, 72). The response 

 was not propagated, being recorded in monophasic 

 form between different positions along the muscle. In 

 the sartorius muscle of the frog, with one electrode 

 kept on the nerve-free pelvic end and the other moved 

 from place to place, the magnitude of the recorded 

 potential change was found to be correlated with the 

 density of nerve endings under the moving electrode. 

 The potential change arising at a focus of nerve 

 endings (recorded with respect to a distant nerve-free 

 point on the muscle) consists of a transient negative 

 deflection having a relatively brief rising phase and a 

 slower return, the later part of which follows an 

 approximately exponential time course. This response 

 has been generally referred to as the endplate po- 



