986 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



exist and many attempts have been made to di\ide 

 them into certain main types. However, the question 

 may be raised whether the type divisions described 

 have any real meaning. 



With the arrangement of the Nissl granules as a 

 criterion the ganglion cells have been divided into 

 two to nine classes {213, 218, 219, 342). The possi- 

 bility of such a classification has been denied by others 

 (78, 374); but, even if this possibility exists, certainly 

 no evidence has been given to show that the cell 

 tvpes obtained differ from each other from a func- 

 tional point of view. 



Another classification has been made on the basis 

 of size. In analogy to studies of the size of somatic 

 nerve fibers and its relation to fiber properties, this 

 approach may be assumed to give valuable informa- 

 tion. Unfortunately, however, no conclusive quantita- 

 tive data are available. The most extensise studies 

 ha\e been made by de Castro (98, 103) who claims 

 the existence ot three size groups which are present 

 in varying proportions in different ganglia. Accord- 

 ing to him the cells ma\' be classified as large (35 to 

 55 11), medium sized (25 to 32 fj.) and small (15 to 

 22 /i). The three groups are represented in the su- 

 perior cervical ganglion of man by 27, 50 and 23 per 

 cent, the corresponding values for the stellate ganglion 

 being 17, 67 and 16 per cent. The classification is 

 interesting from the point of view that it might give 

 an anatomical basis to the three main, well delimited 

 cell pools found by Eccles (see below). It is obvious, 

 however, that de Castro's classification is open to 

 criticism. The class limits are arbitrary and no analy- 

 sis of the size-frequency curve has been made to show- 

 that three different size t\pes really exist and that 

 the cells are not distributed along a more or less 

 normal frequency curve with one peak only. The 

 work of de Castro indicates, however, that there may 

 be real differences between various ganglia. The 

 cervical ganglia and to a lesser degree the thora- 

 columbar ganglia have a relati\ely high proportion 

 of large and small nerve cells in contrast to the pre- 

 vertebral ganglia which have practically no cells of 

 such a size and therefore show a more uniform picture. 

 This has been found to hold good for .several mammals 

 and might ob\iously be of significance to neuro- 

 physiological work as there is evidence that fiber 

 size is correlated with the size of the nerve cells (cf. 



356). 



The most commonly used classification is leased on 

 the morphological appearance of the dendrites. The 

 types I (many short dendrites) and II (varying num- 

 bers of long dendrites) of Dogiel have generally been 



adopted to differentiate the ganglion cells into two 

 main groups assumed to represent two cell types 

 clearly differentiated from each other (cf. 177, 180, 

 403). Great variations and many cells belonging to 

 neither group ha\e been observed, however (98, 403). 

 The most representative view is that the nerve cells 

 in the autonomic ganglia (the enteric plexuses ex- 

 cluded) of various mammals have predominantly a 

 large number of long processes, often branching ex- 

 tensively, and that only a small number ha\e short, 

 intra- or extracapsular dendrites (98, 103, 248, 249, 

 352, 403). The ciliary ganglion and maybe other 

 cranial parasympathetic ganglia are exceptions in 

 .so far as they seem to have numerous type I cells 

 (98, 103, 343). Mainly on the basis of the morphology 

 and arrangement of the dendrites, de Castro (98, 

 103) claims the existence of five cell types. There is 

 not as yet more direct evidence concerning the func- 

 tions of the different ganglion cells. 



A new and interesting approach with ganglion- 

 stimulating and ganglion-blocking agents has been 

 used by Shaw and his associates (381-383). Their 

 experiments show that the cells in sympathetic ganglia 

 are not a homogeneous population from a pharma- 

 cological point of \iew and give some support to the 

 hypothesis of Bishop and Heinbecker that distinct 

 cell groups exist in the ganglia, each suijserving a 

 particular function. 



Cotmections Between Preganglionic and 

 Postganglionic j\eurons 



That there ma\- be many more nerve cells in an 

 autonomic ganglion than the preganglionic fibers 

 supplying it was shown b\' Billingsley & Ranson (22) 

 who found the ratio of myelinated fibers to cells to 

 be I :32 in tlie superior cervical ganglion of the cat. 

 Wolf (442), including unmyelinated fibers in the 

 counts, found in two cats a ratio of i:ii and 1:17. 

 In contrast to this, the ratio for the cat ciliary ganglion 

 is approximately 1:2 (442). The obvious difference 

 between the two ganglia has often been taken as 

 evidence for a more diffuse distribution of the sym- 

 pathetic system. As no systematic studies comparing 

 ganglia belonging to the two divisions have been 

 made, howe\er, there is no basis for such a generaliza- 

 tion. As a matter of fact, observations made by Harris 

 (191) suggest the existence of a 1:2 ratio in the in- 

 ferior mesenteric ganglia of the cat. 



It may be concluded from the studies referred to 

 above that in many instances several or even numer- 

 ous ganglion cells are supplied ijy indixidual pre- 



