130 



PHYSIOLOGICAL TRIGGERS 



eserine and DFP. The plane surface excitable membrane (4) and the relatively- 

 short {ca I cm) length of the electroplaque, as well as intracellular recording, 

 permitted detection of the decrementally propagated response. The latter was 

 probably missed in the earlier work with axons, in which conduction block was 



Fig. 4. Differentiation between synaptic and direct excitability in eel electroplaques. 

 A-F: direct stimulation of the cell; A'-F': a weak neural volley; A"-F": a neural volley 

 strong enough to elicit a spike; A"'-F"': su])ramaxinial stimulus to the nerve. Upper row: 

 Activity in the normal cell. Acetylcholine plus eserine was then api)lied. B-B'": the spike was 

 depressed after 114 min. Sui)sef|uent records at 123, 142, 153 and 156 min. The stronger neural 

 volley evoked a larger, i.e. graded response than did direct stimulation. As depolarization de- 

 veloped, block of the electrically excitable generator occurred, but the p.s.p. was still evoked 

 {F'-F'") while a very strong direct stimulus (F) was without effect. Calibration 100 mv and 

 msec, (from ref. 6). 



the criterion of 'inactivity.' Graded responses localized to the stimulated 

 region are observed in transmembrane recording from squid giant axons 

 poisoned by external application of eserine or by microinjection of various 

 drugs (102, 126). Therefore, while inactivation of the acetylcholine system 

 probably affects and eventually may block responsiveness, its immediacy in 

 electrogenesis is doubtful. 



