176 



DONALD M. MAYNARD 



20 40 60 



STIMULATION FREQUENCY 



Fig. 30. Effect of accelerator stimulation frequency on parameters of ganglionic 

 activity (Homaius). a. Ordinate, spontaneous ganglion activity; abscissa, 

 accelerator stimulation frequency. Vertical lines represent the range, (O) repre- 

 sent means. Diagram of burst in upper left shows an initial portion lasting D msec 

 and a subsequent £ portion consisting of 0-3 impulses. Spikes in the preparation 

 could not be assigned to individual neurons; several cells contribute to the 

 impulse pattern shown, b. Ordinate. D. duration of initial portion of burst. 

 A histogram is given at each stimulus frequency showing the distribution of D 

 during acceleration. The curve is drawn through the mean values of D. Open 

 rectangles represent D for the first two bursts of acceleration, presumably before 

 summation is complete. Note that D decreases with acceleration, c. Relation 

 between D and number of impulses in E. The curves are distribution curves for 

 the D values preceding £"5 with 0,1,2, and 3 impulses. There is a positive correla- 

 tion between shorter D and more impulses in E (Maynard, 1954). 



intervals as found by Terzuolo and Bullock (1958) in Panulirus was never 

 observed, however, and must be rare in normal Homarus ganglia. 



Terzuolo and Bullock (1958) find that accelerator activity often produces 

 depolarizing, facilitating, and summating e.p.s.p.'s in Panulirus follower 

 cells. They consequently ascribe increases in activity during acceleration to 

 the reduced membrane potentials of individual ganglion neurons. If there 

 is a maximum degree of depolarization, this may account for the observation 

 that marked acceleration in Homarus occurs only when the initial burst 

 frequency is below 1 •7-2-0 beats/sec and that there appears to be an 

 absolute rather than a relative maximum for the response to accelerators 



