806 Comparative Animal Physiology 



most nerve cells have the ability to discharge without stimulation by other neu- 

 rones if the chemical environment is suitable. The "spontaneously" active 

 cells can be considered as relaxation oscillators where a continuous source of 

 energy, e.g., oxidative system, stores up potential to a critical value and then 

 the cell membrane breaks down. In this sense such activity is not spontane- 

 ous but rather a response to the chemical environment. Nervous pacemak- 

 ers in hearts have been discussed above (Ch. 15). A classification of ner- 

 vous rhythms is given by Bullock.'^'^' ''^ 



FROG MAN 



Types of CorTical ElecTroqram 

 Occiput Zye5 closed 



Dominant olpho r ^qq 



,^/v\\fvv/\/^/^A^A/^'''\^/^A-^^"A-^^•^'~v.-\/w — AA^A/^'''~~v\yw^v-^/v^/vA.v^^lAAAr~-A.^V^ 

 SubdominanT alpha 



c yA/K^VvvVw 





"Rare alpha 



A B 



FREQOENCY c ^ 5- 



SAL 6.6 ..U im M >i<n^>y 



2K3 CA I V1IN. H.O 



,, ■•^■-— -'-^^; •— - -^- -BiiB tmnii liiiiii 



2" 3 ' f^ " 5-0 Ml 



iipiiiUMikMia>iiiBiiiilii|iwiiai(iMiMiiii |i i iniifaumi 



Fig. 304. Types of rhythmic activity in central nervous systems: A, Synchronized 

 spontaneous rhythm from isolated olfactory bulbs of frog: a, freshly isolated bulb; h, 

 small isolated bit of bulb; c, after 30 min. in Ringer; d, single separated bulb; e, control 

 on optic lobe some time after isolation. Time, horizontal line— 1 sec. From Libet and 

 Gerard.""" B, Electroencephalograms of different men recorded from skin over occipital 

 lobes with eyes closed. From Davis and Davis."" C, Spontaneous activity in isolated 

 abdominal ganglion of crayfish, showing asynchronous rhythms in several designated 

 neurones. Increase in potassium content of saline by two times and in calcium content 

 by three times causes initially an increase and later decrease in frequency. Letters identify 

 imnulses in individual neurones. From Prosser."™ 



Asynchronous Spontaneous Activity. In some nerve centers each neu- 

 rone is independent of other neurones, although a given cell may discharge 

 more or less rhythmically, different neurones having different frequencies. 

 Such asynchronous activity is found in ganglionic nervous systems of anne- 



