HARRY GRUNDFEST 



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fiber. In some muscle fibers, specific neural paths produce inhibitory effects 

 which may be manifested as a hyperpolarizing p.s.p. (74). 



The 'slow' muscle fiber associated with the crayfish stretch receptor is dif- 

 fusely innervated, and responds to neural stimulation with a long-lasting, end- 



FiG. 5. Interaction of the directly elicited muscle fiber spike and an end-plate potential. 

 Upper left: The responses labeled M in / and 5 show the direct spikes of the muscle fiber 

 recorded at the end-plate region. The response N in record 2 is that obtained by stimulating 

 the nerve. The directly elicited spike is distorted by superposition of the neurally evoked e.p.p. 

 in the other records. Arrows mark the onset of the response to a neural stimulus. Right: A 

 reconstruction of the same records, showing how the direct spike is distorted {M N) when the 

 neural stimulus is delivered at different phases of M. The e.p.p. of the neurally evoked spike 

 {N) is seen in the upper tracings (.4). Lower left: A diagrammatic representation of the events 

 The e.p.p. adds to the spike when the latter is more negative than an equilibrium potential of 

 — 10 to —20 mv. It subtracts from the spike when the latter is more positive than the equi- 

 librium potential (composed from ref. 37). 



plate type of potential. On the other hand, the 'fast' muscle fiber exhibits both 

 an e.p.p. and a spike (133). These muscle fibers also show anatomical differ- 

 ences, and are supplied with different receptors, slowly adapting and rapidly, 

 respectively (133, 188). 



