4: Origins of the Receptor Potential 



In Chapter 2 evidence was advanced which indicates that the 

 receptor potential is generated in areas of the sensory cell 

 membrane which are electrically inexcitable and are, therefore, 

 physiologically different from regions which support regenerative 

 electrical activity. Time-dependent processes in the electrogenic 

 membrane, for example, are of little importance in determining the 

 waveform of the receptor potential. The changes in membrane 

 permeability which are responsible for its generation are, in fact, 

 maintained throughout the period that the stimulus is energetically 

 hound to the sensory membrane. Secondary uncoupling of 

 stimulus energy from the sensory cell can occur, as was discussed 

 in the preceding chapter, although this seems to be largely a 

 function of the accessory structures alone. This latter process 

 thus occurs at functional levels in the sensory process which are 

 separate from changes in permeability of the cellular membrane. 



The receptor potential which occurs in a primary sensory 

 neuron or a sensory cell is an IR drop which is generated by 

 current flow through the electrical resistance of inactive membrane 

 regions. This latter current results from the movement of ions 

 through loci where the resting permeability of the membrane has 

 been altered by the transduction of stimulus energy.* 



This chapter will be devoted to a review of the evidence that 

 (i) the absorption of stimulus energy leads to a decreased mem- 

 brane resistance, resulting in the inward flow of ionic current, 



• The conventions which define the electrical polarity of these changes are 

 similar to those used with regard to electrically-excitable membrane; thus, the 

 current due to an inward movement of positive ions at the transducer locus 

 will cross adjacent membrane regions in an outward direction, thereby dis- 

 charging the membrane capacitance and depolarizing the cell. 



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