CARDIAC INHIBITION IN DECAPOD CRUSTACEA 171 



100 



o I 



100 



\ 



i .V.I 



SECONDS 



Fig. 25. Inhibition of spontaneous ganglion activity, primary effect on pacemaker 

 (Paniilirus). Continuous plot of activity against time. (O) and (#) represent large 

 unit spikes; ( + ), the first of a brief train of pacemaker impulses. Burst activity 

 is indicated by a sudden increase in single unit activity. Note the correlation 

 between absence of pacemaker impulses and absence of bursts (Maynard, 1954). 



When this is combined with spontaneous activity in followers, the pattern 

 of Fig. 25 may occur. The released followers discharge in continuous runs 

 at sHghtly subnormal frequencies, and reorganize into bursts only with the 

 reappearance of the effective pacemaker. Patterns such as this were found 

 only in injured preparations, so they may rarely occur in normal ganglia. 

 The inefficiency of such disorganized activity or fibrillation in pumping fluid 

 through the heart is obvious. 



Inhibition and Patterning, Discussion 



Both the isolated and interacting unit decrease their mean discharge fre- 

 quency upon inhibition. In the isolated unit such a decrease is usually accom- 

 panied by a corresponding decrease in all pattern parameters (Fig 13). In 

 the interacting unit, the parameters may be relatively independent, and the 

 mean frequency decrease accomplished by several combinations of pattern 



