EXCITATORY AND INHIBITORY PROCESSES 



305 



level of membrane potential at which the inhibitory potentials reverse their 

 polarity and this indicates the inhibitory "equilibrium level" or "reversal 

 potential". In other words, the inhibitory action tends to restore the mem- 

 brane potential if it is displaced in either direction by stretch. A similar picture, 

 but this time complicated by normally occurring sensory discharges, has been 

 obtained from rapidly adapting receptors (Fig. 14, lower portion) and from 

 slowly adapting cells (not illustrated). 



Hagiwara et al. (1960) have studied the effects of changing the resting 

 membrane potential of slowly adapting cells by means of appHed currents 

 and observed a linear relationship between the magnitude of the membrane 

 potential change and the amplitude of the inhibitory postsynaptic potentials. 

 The findings of these authors, using applied currents, are similar to those 

 obtained by Kuffler and Eyzaguirre (1955) although the former displaced the 

 membrane potential to a greater extent, since the latter only used stretch 

 and relaxation as means of changing the magnitude of the membrane 

 potential (Fig. 15). 



These experiments demonstrate that the membrane effect produced by 

 inhibitory impulses depends on the state of the sensory receptor cell and this 

 is true both for the fast and the slowly adapting cells. At certain membrane 



H. 



40 mV 



- 30 - 



-40 -20 



MEMBRANE POTENTIAL CHANGE 





-20 



Fig. 15. Relations between the amplitude of the inhibitory junctional potential (on 

 the y-axis) and the change of membrane potential (on the A'-axis) by applied 

 current from the resting potential level. The amplitude of the depolarizing junc- 

 tional potential or the depolarization of the resting membrane potential is 

 positive on each axis. Open circles and full circles were obtained from the recording 

 with K2SO4 filled and KCl filled internal electrodes respectively. (From Hagiwara, 

 Kusano and Saito, 7. Neiirophysiol. 23 : 505-515, 1960.) 



