Muscle and Electric Organs 



599 



Wiersma and his associates found that the branching of axon terminations 

 on crustacean muscle is extensive, forming a sort of network."*' They postu- 

 lated that conduction in the muscle is entirely by the nerve elements and 

 that within each muscle fiber there are separate contractile systems each ac- 

 tivated by its own nerve fiber. Inhibition is most effective oh slow contrac- 

 ti(ms and can act either between nerve impulse and muscle potential or be- 

 tween muscle potential and contraction. 



Evidence for a different interpretation of the fast and slow systems has 

 been presented by Katz and Kuffler.'^"- ^^■* A muscle consisting of many 

 parallel fibers (extensor of carpopodite in crab or crayfish) was exposed and 

 stimulated directly; simple diphasic impulses which were propagated as in 



Fig. 231. Electrical responses from extensor of carpopodiie of crab to paired shocks. 

 Interval between stimuli to fast axon successively from above 24, 12, 9.6, 8, 6.4, and 4.8 

 sec. End-plate jxjtentials to second shock show summation and propagated spike appears 

 in lower 3 records. From Katz and Kuffler."" 



vertebrate skeletal muscle were recorded. In other preparations some nerve 

 branches were cut, leaving isolated branches intact; when the nerve was then 

 stimulated and a recording electrode moved about on the muscle, local nega- 

 tive potentials with all of the properties of the vertebrate end-plate potentials 

 (e.p.p.'s) were observed (Fig. 231). The fast system has large e.p.p.'s which 

 give rise to conducted muscle spikes; the "fast" e.p.p.'s show little facilitation. 

 The fast system fatigues rapidly, the excitatory process falling to one half 

 in 5 msec. The "slow" system, on the other hand, has small e.p.p.'s which 

 show much facilitation; at frequencies of 50 per sec., for example, the e.p.p. 

 grows to 3 times its initial size, and at 150 per sec. the e.p.p. reaches a plateau 

 5 to 10 times that at 50 per sec. At low frequencies (lO/sec), stimulation 



