Parasympathetic Secretory Innervation 43 



systemic blood pressure (Babkin, Alley and Stavraky, 1932). 

 Physiologically, however, a salivary cell does not seem to have to 

 depend for its excitation on transmitter substance from para- 

 sympathetic fibres of neighbouring cells. On the contrary, each 

 cell seems to have a rich supply of parasympathetic fibres, several 

 parasympathetic neurones converging on to the secretory cell. This 

 was concluded by Lundberg (1955) from experiments of the type 

 shown in Fig. 3.1. The membrane potential was recorded using 



Fig. 3.1. "Type 1" responses obtained with intracellular electrode from the 

 cat's submaxillary gland. 



Showing increasing response with increasing strength of single shock stimulation to chorda. 

 Supramaximal stimulation in record to the right (Lundberg, 1955)- 



an intracellular electrode. It was found that with increasing strength 

 of the single shocks, applied to the chorda, the hyperpolarization 

 increased. Some experiments, in which the potential grew stepwise 

 with increasing intensity of stimulation, allowed the conclusion 

 that the secretory cell is innervated by a minimum of 5-10 neur- 

 ones. The fibres stimulated were of course preganglionic, and 

 further experiments on a preparation, in which postganglionic 

 parasympathetic stimulation is possible, would be of great interest. 

 Numerous investigators have demonstrated that the transmitter 

 of the parasympathetic nerve fibres, which cause salivary secretion, 

 is acetylcholine. Acetylcholine can be extracted from the salivary 

 glands. After section of the chorda tympani the amount extractable 

 decreases, according to Chang and Gaddum (1933). Beznak (1932, 

 1934), however, found no such reduction in the acetylcholine con- 

 tent. It is interesting to observe that according to Chang and 

 Gaddum all the acetylcholine does not disappear even after section 

 and degeneration of postganglionic fibres (in the parotid gland). 

 This may suggest that acetylcholine has a function in the gland 

 apart from that as a transmitter; but it should also be kept in mind 

 that there is some evidence showing that cholinergic fibres reach 

 the parotid gland through anatomically unknown channels. Chohn- 

 esterase, predominantly of the specific type, is present in salivary 



