i 794 



IIANDHOOK. ()!• PHYSIOLOGY 



NEUROPHYSIOLOGY III 



table i. Distribution of Cell Types 

 m Rut Cerebral Tissues* 



Sample 



Mixed cerebral 

 cortex 



Corpus callosum 



I white) 

 Cerebellar cortex 



rota! i i Us 

 9.6 



7.8 



\: : 



Neurons 



G1U1 

 5-8 



7.6 



[.ll.lnllirll.l! 



Cells 

 I .6 



* Numbers of cells X 10" per gpm weight, according to 

 data of Nurnberger (158) and of Pope (1771 

 t Percentage of glial types: 



Gray matter 

 White matter 



Astrocytes Oligodendroglia Microglia 



40 52 8 



3° 65 5 



because the available data are too scattered and 

 incomplete. And embryological and developmental 

 aspects would seem to be beyond the scope of this 

 chapter, but ma\ be obtained from several good 

 sources (65, 242). It has seemed more important 

 to attempt to indicate how the basic components are 

 organized into a functioning tissue fabric. At best, 

 the separation of structure from function is an arti- 

 ficial convenience; but, since the details of metabolism 

 and function are covered in succeeding chapters, the 

 latter will not be stressed here. It must be remem- 

 bered, however, that the framework of neural tissues 

 is not simply a -tatic support but is in actuality 

 composed to a large degree of the lipid and protein 

 moieties of enzyme sv stems which are the sites of 

 metabolic activity and the loci for conduction and 

 transmission potentialities. 



COMPOSITION OF THE CENTRAL NERVOUS SYSTEM 



Mm tin hemical Data 



The first chemical fact ascertained about the brain 

 w as a report bv Hensing in 1719 (iOl) of its prominent 

 phosphate content. By 1K11 when the lust analysis 

 of human and animal brain was published by Yau- 



quelin (236), investigators had a surprisingly good 

 concept of its composition. Vauquelin reported the 

 following composition foi whole brain (236, p. 232): 



1 " I. .in. en\ 1 



Matiere u'i asse blanche 



Mai i' 1 e '.'i .iss. 1 ougeati e 



I \ll1111nine 

 1 Ismazome 

 6 Pho phoi ■ 

 7 ." Acide, seK. ioufi 1 



The lipid percentage is low, since Vauquelin 

 employed only alcohol as extractant, but the protein 

 (albumine) and water are comparable to present 

 analyses. Among the salts, Vauquelin recognized the 

 presence of potassium, calcium and magnesium plus 

 a little sodium chloride. He also reported the higher 

 lipid content of brain stem and spinal cord, and the 

 high protein content of nerve. He suggested that the 

 phosphate was derived from lipid, and that protein 

 and lipid were probably structurally associated. 

 (The osmazorru listed was a term used to describe a 

 water-soluble tissue extract, containing peptide- and 

 alkaloid-type substances similar to a meat broth or 

 extract.) Considering the dearth of analytical methods 

 and the embryonic concepts of organic chemical 

 components at that time, Vauquelin and his con- 

 temporaries had an excellent understanding of 

 cerebral composition which is not too different from 

 modern ideas. 



Space does not permit a review of the interesting 

 history of the development of brain chemistry, but 

 the summaries by Thudichum (222, 223), Schmitz 

 (204), Winterstein (2491, Page (it>8), Rossitei iu|i] 

 and Tower (229) cover the period in detail. The 

 early investigations culminated in the brilliant 

 studies of Thudichum between 1862 and 1901 which 

 are reported in his two books on the chemical consti- 

 tution of the brain (222, 223). Many of the com- 

 ponents of the cerebral lipids which are familiar 

 today were first isolated and identified by Thudichum. 

 His analyses of gray and white matter give sjood 

 approximations to those of today. Thudichum's work 

 brought an end to .m era ol uncertainty and con- 

 fusion about the composition ol' the brain and ushered 

 in the modern era of investigation on its finer 

 structure, metabolism and mode ol functioning which 

 are reviewed in the references cited above. 



PRINCIPAL DIVISIONS \M> CONSTITUENTS. Fluid ip 

 anil solutes. The principal divisions and constituents 

 of the central nervous s\stem are shown in figure 1. 

 The most striking feature is the tact that brain 

 consists mosti) ol water. Infant brain has an even 

 higher percentage I about 90.5) for both gra) and 

 white matter (1171. This situation is mil unique to 

 brain since ii is typical of most organs of the body. 

 There is excellent agreement on the total amount of 

 water in brain, but its conipartnientation between 



extracellular and intracellular spaces is still con- 

 troversial. The preceding Chapters have considered 

 this and related aspects in detail, so that only relevant 



factors need lie covered. Despite objections (9) and 

 proposed 1 lifications 55, 67, 251)1 it is still 



