438 ANNALS NEW YORK ACADEMY OF SCIENCES 



highly resistant transverse membrane. This evidence for ganglionic 

 synapses also obtains for neuro-muscular junctions. 



B. That, in general, the surface membranes of figure 5 have the 

 electrical properties demonstrated for peripheral nerve and muscle 

 membranes: resistance, electromotive force, capacity, and rectification, 

 as shown in figure 1. There are no direct observations on nerve cells, 

 but they resemble nerve fibers in their electrical excitability and in 

 the propagation of impulses from a nerve cell to its axon,^''' ^^' **° and 

 vice versa. ^°' ^^' *^''' "^ It may also be assumed that both the exterior 

 and the interior of the cells are good conducting media, and that the 

 resting potential of the post-synaptic membrane is identical with that 

 for the remainder of the post-synaptic cell.^^ 



C. That the synaptic region of the post-synaptic cell has unique 

 electrical properties, in that cathodal polarization (lowering of resting 

 charge) sets up a graduated "local response," with a temporarily ir- 

 reversible and large diminution of electromotive force and resistance, 

 but not the all-or-nothing membrane "breakdown" characteristic of the 

 propagated impulse (cf. part 3, B and D). Direct evidence is only 

 available for the end-plate region,^" but the assumption is extended to 

 the synaptic regions of nerve cells. 



5. DEVELOPMENT OF HYPOTHESIS ON THE BASIS 



OF THIS MODEL 



It appears that, assuming A and B, we have to expect that the cur- 

 rent generated by an impulse propagating up to the terminal of the pre- 

 synaptic fiber will, in part, penetrate the post-synaptic cell and give 

 a diphasic action (cf. part 3, C, iii). Firstly, there will be an anodal 

 focus, Ai, at the synaptic region, with a cathodal surround (figures 

 5a and 6a). Then, when the active region of the impulse reaches the 

 terminal, current flow will reverse, giving a cathodal focus, C2, with an 

 anodal surround (figures 5b and 6b). The penetrating current will 

 be limited by polarization of the membrane and, in the initial phase, 

 by the increasing resistance of the localized anode (rectification effect) . 

 On account of its much larger area, the membrane resistance (and pene- 

 trating current density) at the cathodal surround will be so much lower 

 that its simultaneous diminution by the rectification effect will be 

 relatively insignificant in tending to increase the flow of penetrating 

 current. However, in the second phase, the situation is reversed, be- 

 cause, on account of the high current density, the lowering of the initi- 

 ally high resistance at the localized cathode will have a preponderant 

 effect in increasing the flow of current. Hence, due to rectification, the 



