24 : 2/ The Molecular Basis of Nerve Conduction 



441 



diagrammed in Figure 2. The analog integrates these changes over a 

 long period of time ; some may be more readily observed in the analog 

 than in the conducting axon. 



Other experiments support this analog. Spike potentials usually 



External 

 Medium 



Axon 

 Interior 



►++++ ♦+ + — - + \ \+ » • 



Membrane 



About to k Recovering 

 be Excited 



Spike 



Figure 2. Current patterns near a spike conducted along an 

 axon. After J. M. Tobias, "Nerve Ultrastructure and 

 Functions," in Modern Trends in Physiology and Biochemistry, 

 E. S. G. Barron, ed. (New York: Academic Press, Inc, 1952). 



Cathode 



External 

 Medium 



Axon 

 Interior 



Membrane 



Figure 3. Current patterns for subthreshold d-c stimulus 

 applied to an axon. Note similarity of current patterns inside 

 axon in Figures 2 and 3. After J. M. Tobias, "Nerve Ultra- 

 structure and Functions," in Modern Trends in Physiology and 

 Biochemistry, E. S. G. Barron, ed. (New York: Academic Press, 

 Inc., 1952). 



start near a region of cathodal polarization. Conduction rate is faster 

 near an external cathode, slower near an anode. Anodal polarization 

 relieves blocks caused by chemical agents producing depolarization. 

 These all can be predicted from the analog. That it is only an analog, 

 however, is emphasized by the observations that anodal polarization also 

 relieves chemical blocks not associated with depolarization, contrary to 

 the predictions of this analog. 



In an axon polarized by a subthreshold direct current, various changes 

 are seen. By and large, opposite changes occur near the cathode and 

 anode. These changes are represented in tabular form on page 442 

 and then discussed briefly. 



