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ANNALS NEW YORK ACADEMY OF SCIENCES 



(b) 



(c) 



(d) 



Figure 7. (a) Monophasic pre-synaptic action potential, (b) Its first derivative (dotted line) 

 giving the time-course of the post-synapfic penetrating current (part 3, C), anodal currents being 

 plotted downwards. The broken line shows the modification produced in this current if resistance 

 is doubled at the anodal focus and halved at the cathodal focus (rectification). The continuous 

 line gives the approximate time-course of the post-synaptic membrane potential so produced, al- 

 lowance being made for the electric time constant of the membrane (cf. Katz & Schmitf", figure 

 6). (c) Post-s>naptic membrane potential shown as in (b). At X, the local response of the syn- 

 aptic membrane is initiated by the catelectrotonic phase, and it is shown running a time-course 

 rather slower than a spike, (d) Neglecting the passive electrotonic changes of (b) and (c), this 

 local response is plotted together with the time-course of the resulting spreading catelectrotonus, 

 shown as the broken line (the synaptic potential) recorded from the post-synaptic membrane adja- 

 cent to the synapse (e.f/., at arrow, in figure 6d). The rising phase of sin initiated impulse is also 

 shown (dotted line), AZ being its synaptic delay. 



