74 



J. C. ECCLES 



B 



Q -A- 



+ 2r- 



-82 





 -2 

 -4 



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"^ijQo^ 



X. 



\. 



J L 



\. 



-100 



-100 



80 - 60 



(mV) 



40 



Fig. 3a. l.p.s.p.'s recorded intracellularly from a biceps-semitendinosus moto- 

 neuron by means of a double-barrelled microelectrode. The records, formed by 

 the superposition of about forty faint traces, show the i.p.s.p.'s set up by 

 a quadriceps afferent volley. By means of a steady background current through 

 the other barrel of the microelectrode, the membrane potential has been preset 

 at the voltage indicated on each record, the resting membrane potential being 

 — 74mV (Coombs et ai, 1955b). Reproduced by permission from the Joiinml 



of Physiology. 



Fig. 3b. Plotting of measurements from series partly shown in a. Abscissae give 

 the membrane potentials and ordinates the sizes of the respective i.p.s.p.'s. 

 Note that hyperpolarizing i.p.s.p.'s are plotted downwards and depolarizing 



upwards. 



Fig. 3c. Series for same motoneuron, plotted as in b, but i.p.s.p.'s produced by 

 an antidromic volley (Coombs ei cil., 1955b). 



of metabolic energy to ion pumps. Tiie conditions generating the i.p.s.p. are 

 shown in the formal electrical diagram of Fig. 2c, where activation of the 1 

 synapses would cause the momentary (for 1 to 2 msec) closure of the switch 

 in the right element of the diagram. 



Figure 2c leads one to expect that during motoneuronal depolarization 

 there will be a corresponding increase in the size of the vohage driving 

 currents produced by activated inhibitory synapses; hence the increased 

 i.p.s.p. of the three upper records of Fig. 3a is accounted for. Similarly there 



