50 The Physiology of Sense Organs 



neurons (fig. 22). This apparently simple relationship between 

 membrane potential and firing frequency is particularly difficult 

 to explain on quantitative grounds. Some of Hodgkin's earliest 

 studies demonstrated that the rate of rise of the local response is 

 an exponential function nf .mpmbrane depolarization. Since firing V 

 frequency in many nerve cells is controlled to a large extent by the / 

 growth of the local response after each impulse has repolarized 

 the membrane, it follows that spike frequency should itself\ 

 increase exponentially as the generator potential increases in i 



mv 



50 

 40 

 30 

 20 

 10 

 



nA 



0.5 I sec. 



Fig. 21 (A) 



