ECCLES: ELECTRICAL THEORIES OF TRANSMISSION 441 



region of the post-synaptic cell an intense ''local response," which runs 

 through a cycle of increasing and decreasing intensity, much as does 

 the spike of a propagating impulse.''^' ^^' ^^^ ^°' '^ This local response, 

 thus, would outlast the second phase of the penetrating current-flow, 

 and provide a relatively enduring focus, of very low polarization (pre- 

 sumably due to diminution or extinction of the membrane battery) and 

 resistance, through which adjacent regions of the post-synaptic mem- 

 brane proceed to discharge. Such a local response is actually ob- 

 served at an ephapse giving A1C2 interaction.^ Figuee 6d shows the 

 internal and external potentials of a fully-developed local response at 

 the end-plate region, where Kuffler^° finds the potential as high as the 

 spike potential. It is shown as zero transverse membrane potential, 

 since it is not known if reversal of potential occurs with the muscle 

 spike. Also, in figure 6d, the anodal surround (of figure 6c) has 

 given place to a catelectrotonic surround of diminished polarization, 

 which spreads spatially, according to "core conductor" theory. With 

 muscle, it appears that the all-or-nothing spike arises when the mem- 

 brane adjacent to the end-plate is critically depolarized,^" e.g., at the 

 arrow (figure 6d). The synapses of ganglion cells and of moto- 

 neurones of the spinal cord have also been observed to generate such 

 catelectrotonic potentials (synaptic potentials), spreading spatially, ac- 

 cording to core conductor theory.-' ^^' ^^ It has further been shown 

 that, as with the end-plate potential,^*'- " these potentials have a time- 

 course, which may be interpreted as due to a brief, active polarization 

 and a passive exponential decay governed by the electric time con- 

 stant (the product CR, in figure 1) of the membrane.^-' -^ In the 

 present hypothesis, the active depolarizing action is provided by the 

 local response of the synaptic region of the post-synaptic cell, not 

 directly by the currents generated by the pre-synaptic impulse, as has 

 hitherto been assumed in hypotheses of electrical transmission.^"' ^^' ®^' 

 77, 78 There have, however, been suggestions of a possible involvement 

 of a local response.* 



The recent hypothesis of Nachmansohn*'^ is relevant to assumption 

 C, for it would postulate that the local response is due to the action of 

 acetylcholine liberated by the post-synaptic membrane at a critical in- 

 tensity of catelectrotonus {i.e., at X in figure 7c). Such an assump- 

 tion is readily assimilable to the present electrical hypothesis, but its 

 general application to nerve impulse transmission would seem to be 

 falsified by Lorente de No's finding^^ that this transmission is unaf- 

 fected by high concentrations of acetylcholine. 



* Eccles, J. C.21: 369; Lorente de N6, B.««: 449; Arvanltaki, A.^: 103. 



