CHEMOPOTENTIALS IN GIANT NHRVK CELLS 187 



to increase the frequency of the initially autoactive neurons. Further changes 

 in tiie membrane potential and frequency of fuing are characteristic of each 

 cellular type: 



(a) A Cell 



The frequency of firing of the A cell increases when this cell is first depolar- 

 ized by 5-10 mV. When the extent of depolarization exceeds 10 20 mV, the 

 frequency decreases (see Fig. 21 ). 



(b) Br Cell 



The frequency of the slow waves of the Br soma increases when this is first 

 depolarized by about 20 mV. With further depolarization, the slow waves 

 tend to disappear, the spiking becomes continuous and finally the spikes are 

 reduced to damped oscillations (Figs. 21 and 22). 



(c) The A rhythmic Sonmta 



The arhythmic B soma shows an increased frequency when depolarized 

 by no more than about 20 mV. 



V "" "" v-— " 



B 



[_ .XL-. ' — .-..^...>.«..,.^^<»ft^^^^ 



Fig. 21. Effect of carbon dioxide on the activity of the three typical giant somata 

 functionally differentiated. In all cases the carbon dioxide is admitted at the 

 beginning of the recordings (arrow). 



A, Giant soma A, inactive. The carbon dioxide slightly depolarizes the mem- 

 brane and initiates the activity. The frequency reaches a maximum 20 sec after 

 the admission of CO2 and later decreases. Finally the activity ceased a few 

 seconds after the end of the recording (65 sec after the admission of the CO2). 



Br, Giant soma Br, initially autoactive in standard conditions (20 C, 100"^ O2, 

 sea water), by repetitive trains of spikes, lasting about 10 sec. After the 

 admission of CO2 the depolarization starts. At this, the frequency of the spike 

 trains increases. Finally, 30 sec after the end of this recording, the activity of the 

 5rcell degenerates to damped oscillations and the cell stops firing (see Fig. 22). 



B, Soma B; its activity is normally arhythmic: the spiking is interrupted by posi- 

 tive potentials. It is strongly depolarized by CO2 and its frequency is increasing. 

 At the end of the recording one observes a first positive long lasting wave during 

 which all spike emission is inhibited. Two minutes later, after considerable 

 depolarization (almost 60 niV) the activity of the B soma completely ceases. 



Scales for all recordings : 50 m V, I sec. 



