Origins of the Receptor Potential 71 



controlled by the stimulus. Normally, these changes result in an 

 inward current flow at the sensor locus, due to a movement of 

 one or more ion species moving down their electrochemical 

 gradients, which causes a depolarization of the resting membrane 

 in adjacent regions of the cell. It is probable that hyperpolarizing 

 receptor potentials also exist, although these would most certainly 





E SHKl 



-At 



«3 



* — ^WVWWV 



^ — wvwwv- 



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wwwwv 



R IEAKA6E 



REFERENCE 

 ELECTRODE 



: RECEPTOR 

 SITE 



RECORDING 

 ELECTRODE 



Fig. 3 1 . An electrical model of the insect mechanosensory neuron and 

 the recording situation. The recording pipette is separated from the 

 impulse-supporting membrane by an extremely large external resistance 

 (R leakage), by the membrane resistance (/?Af). and by the internal 

 longitudinal resistance of the distal process of the sensory neuron (Ri). 

 The amplitude and polarity of action potentials (E spike) depend upon 

 the ratio of the resistances, RmIR Leakage. When this ratio becomes 

 smaller, due to an increase in membrane conductance, the amplitude of 

 the conducted impulses increase. (From Wolbarsht,^"' Fig. 13.) 



result from the flow of current from entirely different ionic 

 generators. The question now arises as to the ion species which 

 are involved in these respective currents. Now the excitatory 

 receptor potentials depolarize the membrane from its resting level 

 of about —70 millivolts. This depolarization must, therefore, 

 involve the movement of ions with an electrochemical equilibrium 

 considerably below the resting level. It should thus be possible 



