298 



C. EYZAGUIRRE 



The phenomenon just described appears both in slowly and rapidly 

 adapting cells. In some instances, however, an antidromic axon impulse 

 invades the soma-dendrite complex. However, due to various reasons like 

 "fatigue", subnormality, or cell geometry, the magnitude of potential 

 gradients becomes critical for adequate impulse conduction. Thus, when a 

 cell is relaxed it may have a resting potential similar to that of the axon. 

 When the dendrites become depolarized, the soma region can be brought 



Fig. 10. Axon-soma invasion and membrane potential in slowly adapting cell. 

 Left portion, relaxed cell has resting potential of 70 mV. a. Two axon impulses 

 (al, a2) at 40 msec fail to invade cell soma. b. At 13 msec interval a2 invades. 

 c. cr2 is moved closer to a\ during exposure and at 20 msec it propagates into 

 cell soma. The axon-soma delay becomes progressively shorter at small intervals. 

 Right portion, cell slightly stretched, resting potential reduced by several milli- 

 volts. Ai. Both axon impulses invade cell soma. Bi. Second antidromic now 

 blocked at 16 msec interval. Ci. al is moved closer to al and is blocked during 

 after-positivity. Axon-soma delay becomes progressively longer at shorter 

 intervals. After-positivity not well seen at this amplification and stretch. 

 (From Eyzaguirre and Kuffler, J. Gen. Physiol. 39 : 121-153, 1955b.) 



quite near to its firing range by light stretch, and readily triggered by an 

 axonal impulse which failed to do so in the unstretched preparation. The 

 subthreshold excitatory depolarization of the soma should sum with the 

 advancing front of the axon impulse, the latter being speeded up, as shown 

 by shortened axon-soma delay. The failure of invasion by a second axon 

 impulse when the cell is stretched cannot be due entirely to refractoriness of 

 the cell because this occurs at intervals much longer than those associated 

 with refractoriness. It is more hkely that during the positive repolarization 



