172 



HANDBOOK OF PHVSIOLOGV 



NEUROPHYSIOLOGY I 



Fio. 20. Different types of electrical 

 activity in cat salivary gland cells. 

 Depolarization shown as downward 

 deflection in these records. A: Type I 

 cells produce hyperpolarizing p.s.p.'s 

 which are graded with strength of the 

 stimulus. Single shocks to chorda 

 tympani evoke p.s.p.'s which last about 



I sec. B: Type I cells produce only 

 hyperpolarizing p.s.p.'s to excitation ot 

 the sympathetic {upper iigna!) or para- 

 sympathetic {lower signal) nerves. How- 

 ever, the latencies and magnitudes of 

 the p.s.p.'s differ somewhat. C: Type 



II cells develop hyperpolarizing p.s.p.'s 

 on stimulating the chorda tympani and 

 depolarizing p.s.p.'s through their 

 sympathetic innervation. D: Type III 

 cells (which may be myoepithelial 

 elements of the ducts) respond only with 

 depolarizing p.s.p.'s to parasympa- 

 thetic {above) or sympathetic {below) 

 stimulation. The resting potential, 

 about —80 mv, is large in comparison 

 with that of Type I or II cells and 

 resembles that of muscle fibers. E: 

 Type I cells respond with hyperpolari- 

 zation to epinephrine, acetylcholine 

 and pilocarpine. [From Lundberg 

 (144).] F: The hyperpolarizing p.s.p. 

 of the gland cell is remarkably insensi- 

 ti\e to changes of the membrane po- 

 tential. The resting potential was 30 

 mv. [From Lundberg (145).] 



B 



2 sec 



-40 



-120 

 -80 

 -40 

 - 



2 sec 



-50 - 

 -40 - 

 -30 - 

 -20 - 



2sec. 



l/^g adr. 



O.l/ig och. 



-120 

 -100- 



- 80 

 -60 

 -40- 



- 20 



- 



0.5 /ig pilocar. 



effects upon the kinetics of the ionic 'valving' of tiie 

 transducer action. 



The maximum attainable amplitudes of p.s.p.'s 

 are probably determined by electrochemical condi- 

 tions as described in a previous section of this 

 chapter, but these need not be identical for different 

 varieties of cells. Thus, most hyperpolarizing p.s.p.'s 

 reach a limit set by the most negative electrochemi- 

 cal ionic species, but hyperpolarizing electrogenesis 

 of glands can occur in the face of very high internal 

 negativity (fig. 20). These differences reinforce the 

 conclusion (91, 105) that electrical activity of bio- 



logical membranes may involve a variety of mcch 

 anisms, some of which are not yet understood. 



Postjunctianal Cells with Dfpolaii'ing 

 Postsynaptic Potentials 



As noted above, some cells though not electrically 

 excitaijle respond with depolarization to neural or 

 chemical stimuli. Of general interest are electrically 

 inexcitable invertebrate and vertebrate muscle 

 hbers, such as the ' slow' muscle fibers of the frog 

 (fig. 4i4). They are diffusely innervated and neural 



