COMPOSITE ACTION POTENTIAL OF A NERVE TRUNK 221 



The designation A refers to the somatic myelinated fibers; B to the 

 autonomic myelinated fibers; and C to the unmyelinated fibers. Action 

 in each starts with a spike. The only difference between the types is one 

 of duration. The A spike has a duration of 0.4 millisecond, and the C a 

 duration of more than 2 milliseconds. The spike is followed by an 

 after-potential which is much smaller in size and much longer in duration. 



4V 



Speed 



41 m/sec 



a Spike 



Group 

 A 



ij3 22 m/sec 



Single nerve 

 fiber 



-Spike 



Negative 

 after potential 



Positive 

 30 1 40 50 



-r-fr-Tj 



10 20 



60 



7 15 m/sec, . „ . „„ 

 >• '14 m/sec 



10 20 30 



Time in milliseconds 



0.7 m/sec 



200 



Fig. VI-9. The complete action potential of a bullfrog's peroneal nerve recon- 

 structed semi-diagrammatically from oscillograph records. The electrical shock 

 was strong enough to excite all the fibers. Composite curve drawn from data by 

 Erlanger and Gasser [1937]. Insert, similar results from a single mammalian (group 

 A) nerve fiber. 



After-potentials vary as to form, size, and duration, depending on the 

 kind of fiber. The complete sequence is a spike and a negative after- 

 potential followed by a positive potential in the A and C fibers. In the 

 B fibers the negative after-potential is extremely small in single responses 

 but can be developed by special procedures. 



Table VI-1 shows this classification applied by Grundfest [1940] to 

 mammalian nerve fibers. Comparable correlations are not available for 

 the action potentials of invertebrate nerves. 



Grundfest points to two noteworthy correlations in the table: (1) 

 the spike duration is constant for all A fibers within the experimental 

 limits of 0.45 ± 0.5 millisecond and is independent of the size of these 



