ECCLES: ELECTRICAL THEORIES OF TRANSMISSION 437 



end, showed a terminal A2 effect,^* but, presumably, this would dis- 

 appear, closer to the killed end. The ephaptic experiments, in general, 

 show that special conditions must prevail at synaptic contacts, if elec- 

 trical excitation is to be adequate for synaptic transmission (cf. part 8) . 



D. Special Properties of the Synaptic Region 



So far, such investigation has been restricted to the isolated neuro- 

 muscular junction. When electrical recording is effectively localized 

 to the end-plate region of the muscle, it has been shown that the end- 

 plate potential set up by a nerve impulse rises smoothly to the full 

 height of the spike potential,''" w^ithout showing the sudden inflection 

 characteristic of impulse initiation.*^- ^-' "^ The impulse appears to 

 be initiated, a little later, by an adjacent region of the membrane, 

 when it reaches a critical intensity of catelectrotonus. Progressive 

 curarization progressively diminishes the end-plate potential; the im- 

 pulse initiation occurs adjacently, after the longer delay ensuing before 

 the lower end-plate potential builds up the critical catelectrotonus ; and 

 eventually, transmission fails. It may, therefore, be assumed that the 

 end-plate region of the muscle is speciahzed to give "local responses" 

 of high and graduated intensities, without the sudden incursion of the 

 all-or-nothing "breakdown" of resistance and battery that occurs with 

 impulse initiation. ^° This evidence of unique electrical properties 

 of the end-plate is relatable to its well-known, unique, pharmacological 

 properties. ^^' ^*' ^^ In the isolated preparation, Kuffler^^ has failed to 

 detect the large resting potential (positive or negative) between the 

 surface of the end-plate and that of the muscle fiber that has been 

 described by Buchthal and Lindhard.^ 



4. INITIAL ASSUMPTIONS OF HYPOTHESIS 



The following three initial assumptions of the electrical hypothesis 

 are based on the evidence of the preceding four sections, together with 

 the conventional histological picture (they form, as it were, a model 

 of a synapse whose functional operation will be discussed in part 5) : 



A. That the geometrical situation at the synapse may be schematic- 

 ally represented by the pre-synaptic fiber ending as a cylindrical mem- 

 brane, with a closed end in close apposition to the large plane surface 

 membrane of the post-synaptic cell, as is shown in section in figure 5. 

 Histologists are now fairly generally agreed that a transverse mem- 

 brane exists at the synapse,^" and there is also electrical evidence* of a 



* Eccles, J. C.2»: 352. 



