ECCLES: ELECTRICAL THEORIES OF TRANSMISSION 443 



the synapse, would, in general, propagate past the synapse and so exert 

 on the pre-synaptic nerve terminals the full sequence of AiCiC2A2, the 

 terminal A2 cutting short any excitation of the pre-synaptic terminal 

 by CiCo;^ (iil the asymmetry of the pre- and post-synaptic elements, 

 both as regards relative size and convergence relationship;^ (iii) the 

 pre-synaptic terminal may not have the special excitatory properties 

 postulated for the synaptic region of the post-synaptic cell (assumption 

 C). Of these, (i) is susceptible to test with the neuro-muscular junc- 

 tion. Antidromic transmission across synapses has been observed only 

 under the special conditions provided by the prolonged end-plate nega- 

 tivity set up by nerw impulses in eserinized muscle.^' There, the nerve 

 terminal would be sensitized by the currents generated by the localized 

 end-plate negativity.* Moreover, some of the muscle impulses may be 

 blocked at the end-plate by the catelectrotonus.^^- ^^ Thus, such anti- 

 dromic transmission occurs under conditions resembling those causing 

 ephaptic transmission, close to a killed or injured region of nerve (the 

 Hering effect, part 3, C, iii). The present hypothesis would predict 

 that antidromic synaptic transmission would be greatly facilitated by 

 colliding two nmscle impulses at the end-plate region (cf. figure 4b). 

 The pre-synaptic fiber would then be subjected to the greatly increased 

 excitatory action of double strength A1C2 stimulation, and antidromic 

 transmission sliould occur under much less favorable predisposing con- 

 ditions. 



B. Synaptic Delay 



If the initiation of the post-synaptic impulse is always caused 

 by mediation of a synaptic potential of the post-synaptic cell, then 

 true synaptic delay measures the interval between the time of ar- 

 rival at the synapse of the fore-front of the pre-synaptic impulse 

 and the initiation of the synaptic potential. In figure 7a, the time- 

 course of the action potential at the pre-synaptic terminal is shown, 

 and below it (the dotted line in figure 7b), the first derivative, which 

 gives the approximate time-course of the current penetrating the post- 

 synaptic membrane (part 3, C, iii). Allowance for rectification action 

 is made in the broken line of figure 7b. On account of the electric 

 time constant of this membrane, its potential change (the continuous 

 line in figure 7b) is shown lagging behind the current which produces 

 it.f Now, according to the hypothesis, the post-synaptic membrane 

 initiates a local response when the catelectrotonus reaches a critical 

 value, e.g., at the point X, in figure 7c. As shown in figure 6d, this 



* Cf Eccles, J. C, & J. !■. Malcolni.3" Figure 15a, 

 t Cf. Katz, B., & O. H. Schmitt."' Figube 6. 



