EXCITATORY AND INHIBITORY PROCESSES 309 



Fig. 18. Persistence of generator potential during antidromic impulse. Intra- 

 cellular records from a stretched slow receptor. Lower portion only of a large 

 impulse is seen. a. An antidromic impulse at arrow sent into the cell shortly 

 after an orthodromic discharge. The repolarization phase of both impulses 

 reaches the same level, b. Two inhibitory impulses precede the antidromic. 

 c. During peak of antidromic repolarization phase a third inhibitory impulse 

 further polarized, indicating that distal dendrite portions were still depolarized. 

 Dotted line drawn through membrane level to which antidromic impulse 

 repolarized. (From Kuffler and Eyzaguirre, J. Gen. Physiol. 39 : 155-184, 1955.) 



clear that the generator potential is not completely wiped out during the 

 repolarization phase of the orthodromic discharge or of the antidromic 

 impulse. (2) The inhibitory potential effectively abohshes the remaining 

 generator potential. 



The phenomenon just described does not occur always and is strictly 

 dependent on the equilibrium level of the inhibitory potential, in fact, if the 

 inhibitory equilibrium potential is at a value significantly less than the resting 

 potential, the repolarization phase of an orthodromic or an antidromic 

 discharge will bring the membrane potential to values greater than those of 

 the reversal potential for inhibitory action. In such a case inhibitory stimula- 

 tion during the peak of repolarization of an antidromic or orthodromic spike 

 may produce a sinall depolarization since the inhibitory action tends to drive 

 the membrane toward the inhibitory equilibrium level. 



The more commonly occurring effects of inhibitory activity on antidromic 

 invasion of the soma dendrite complex are changes affecting the after- 

 positivity of an antidromic spike set up during an inhibitory train. For 

 instance, if a cell is depolarized by stretch and an antidromic spike is sent 

 through, a prominent after-positivity is recorded. However, if this antidromic 

 spike arrives at the soma during an inhibitory train (which by itself produces 

 a hyperpolarization) the after-positivity of the antidromic spike is completely 

 wiped out. If. on the other hand, the cell is relaxed, the antidromic spike 

 shows only a small or short after-negativity. If the antidromic spike is sent 

 through and falls in the middle of the depolarization produced by inhibitory 

 activity, the repolarizing phase of the antidromic potential is blocked (Fig. 

 19). Under normal circumstances an antidromic volley sent through at a 



