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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



The classic work of Langley led to the conclusion 

 that the autonomic ganglia act solely or mainly as 

 relay or distribution stations in the peripheral path- 

 ways. Querido (348) seems to have been the first to 

 question this view seriously on an experimental basis, 

 suggesting that a ganglion has the ability to transform 

 the ingoing impulses to an optimal frequency. From 

 a comparison of the contractions of the nictitating 

 membrane on pre- and on postganglionic stimulation, 

 strong, although indirect, evidence was obtained that 

 the superior cervical ganglion does not alter the fre- 

 quency of the incident impulses (51, 247, 420). 



More direct results concerning the functions of the 

 autonomic ganglia were obtained with the new neuro- 

 physiological methods introduced in the early thirties. 

 At maximal preganglionic stimulation each pre- 

 ganglionic volley gives ri.se to a maximal postgan- 

 glionic volley, the discharge rate jjeing the same as the 

 stimulation frequency (25, 117, 118). It was also 

 observed that no after-discharge occurs until the 

 stimulation frequency is well above the upper limit 

 of the physiological discharge rate (47-49, 123, 275). 

 Observations on the discharge of individual post- 

 ganglionic neurons confirmed the results oijtained 

 from the studies of whole ganglia or large ganglion 

 cell groups (44, 47, 49, 276). This one-to-one relation- 

 ship between ingoing and outcoming impulses was 

 the first discovery of fundamental importance for the 

 relay hypothesis. 



In the basic works of Bishop & Heinbecker (25) 

 and especially of Eccles (117, 118), it was demon- 

 strated that each of the preganglionic fiber groups 

 (Si to S4 according to Eccles) to the superior cervical 

 ganglion in the cat makes synaptic connections with 

 a particular ganglion cell pool without any appre- 

 ciable overlap, thus showing the existence of four 

 different cell groups not connected with each other. 

 This was on the whole confirmed by Rosenblueth & 

 Simeone (371), but they concluded that the S4 cell 

 group may to some extent be supplied also by Si and 

 So fibers. In other ganglia no such high degree of 

 differentiation has been found (cf. 273, 293, 294, 330, 

 440). 



Of greater importance for our understanding of the 

 ganglion construction were the observations of Eccles 

 (118, 119). He showed that there is a convergence of 

 several preganglionic fibers on to each ganglion cell 

 in the Si and S2 cell pools and that a single impulse 

 in a single preganglionic fiber excites the ganglion 

 cells supplied by the fiber suijliminally only, simul- 

 taneous impulses arriving from other fibers being 

 nccessarv to set up a discharge. The convergence 



principle has been found to hold good for the inferior 

 mesenteric ganglia (293, 294, 310J and the stellate 

 ganglion (276). In the latter ganglion Job & Lund- 

 berg (232) showed that an occlusion of more than 

 70 per cent may be observed between the ganglion 

 cell pools excited by fibers from the third white ramus 

 and from lower segments. In the ciliary ganglion, 

 however, no overlap between different preganglionic 

 pathways to the main ganglion cell groups could be 

 demonstrated but seems to exist within a minor group 

 (440). As in the Si and Sj cell pools of the superior 

 cervical ganglion an appreciable subliminal fringe 

 has been observed in the stellate ganglion (276), but 

 contrary to this the cells in the inferior mesenteric 

 (293, 294) and in the ciliary ganglion (440) receive 

 enough synaptic endings from an individual pre- 

 ganglionic fijjer to be supraliminally excited. Another 

 important finding was that ganglion cells subliminally 

 excited by a single impulse could be brought to dis- 

 charge by trains of impulses (44, 118, 121, 276). 



The demonstration of overlap, subliminal fringe 

 and occlusion, and of the po.ssibility of spatial and 

 temporal summation within autonomic ganglia clearly 

 indicates that the ganglia may have activities and 

 organization like those found in the central nervous 

 system. The basic evidence for the relay hypothesis, 

 the one-to-one relationship between ingoing and 

 outgoing impulses and the nonexistence of after-dis- 

 charge, may thus be inconclusive in part at least. 

 As pointed out by Bronk (44) there is a more or less 

 rhythmic bombardment of the ganglion cells by 

 impulses from the autonomic centers, and impulses 

 of varying frequency may arrive at a postganglionic 

 neuron from several preganglionic fibers. This makes 

 it possible for the demonstrated mechanisms to come 

 into action and a ganglion may thus modify the inci- 

 dent impulses and show coordinating activities. The 

 demonstration of short- and long-lasting states of 

 facilitation and inhibition in the synaptic terminals 

 and the postganglionic neurons (120, 122, 124, 232, 

 274, 296) further accentuates the possible existence 

 of such activities. Unfortunately, however, there is 

 no evidence directly showing how the presumed in- 

 tegrative activities work and in what way they modify 

 the impulses from the autonomic centers and what 

 significance they have for the regulation of different 

 effectors. That a group of ganglion cells may be con- 

 nected to separate sets of preganglionic fibers emerg- 

 ing from different spinal segments presumably makes 

 it possible for different afferent reflex mechanisms 

 to control a particular effector, but this does not 

 give any clue to the other problems. That integrative 



