'796 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 







II 

 R - C - 



R' - C - 



II 

 



CH 

 I 2 



CH 



I II 



CH - - P - - 



I 

 OH 



L-g-PHOSPHOGL Y C E R I D E 



I CHOLI NE 

 < ETHANOLAMINI 



L - SERINE 



/ 



CH - 







II 



P - 



- CH, 



CH - 



CH 

 I 

 CH 



- 





 II 



p - o - 



OH 

 PL ASMALOGEN 



CH, 



CH 



HOCH 



HOCH HC 



\ / 



CHOH 



HCOH OH 



I 











II 



P - 



I 



OH 



DIPHOS PHOI NOSI T I D E 



R' 



OH 

 I 



CH 

 I 

 ! - NH - CH 

 I 

 X - - CH, 



ETHANOL AMINE 

 CHOLINE, ETC. 



PHOSPHORYL CHOLINE 



GALACTOSE ( 1 H,SO ) 

 Z 4 



HEXOSES + NEURAMINIC ACID 



SPH INGOSIDE 



fic. 2. The basic structural formulas of the constituent compounds of neural lipids. (Cf. table 

 2.) H and R' indicate fatty acid chains, esterified with glycerol, inositol or sphingosine. The point 

 of attachment of the nitrogen or carbohydrate compound is indicated by .V. The sphingolipids 

 (sphingosides) indicated are sphingomyelin, cerebrosides and gangliosides, respectively (13, 38, 

 7«, '83). 



in vitro (55) and with in vivo space measurements 

 (251) have not been resolved and are complicated by 

 tissue swelling in vitro and the blood-brain barrier 

 phenomenon in vivo. However, the studies of Hiatt 

 (1041 in vivo and of Thomas & Mcllwain (221) in 

 vitro on chloride ion depletion by replacement with 

 nitrate clearly indicate that the chloride ion in brain 

 is in complete equilibrium with serum chloride 

 whereas some sodium and the bulk of the potassium 

 in brain are not. Thomas & Mcllwain (221) found 

 thai only about 2 mEq per kg could be considered 

 .is possible intracellular chloride. 



Willi minor reservations it seems safe to assume 

 that the chloride space is equivalent to the extra- 

 cellular space, or some 30 per cent of the total brain 

 mass, most of which is interstitial rather than cerebro- 

 spinal in location. On this basis the concentration of 

 ions per kilogram ol extra- or intracellular water can 

 be calculated and such values are given in figure i. 

 Direct estimations on neurons suggesl thai their 

 water and solids contenl approximates that given for 

 intracellular total space (water plus solids) of gray 

 in. hi. 1 in figure 1 (31, 32, 14:5, 146, 159). Analogous 

 studies on glia have nol been reported, [f the situation 

 in figure 1 is correct, there is a considerable deficil ol 

 intracellular anions compared to the calculated 

 cation concentration (149). This is presumed to i»- 



made up by the intracellular proteins and lipids. 



each accounting for about half the required amount 

 (67, 153). However, a portion of the intracellular 

 potassium is intramitochondrial (no) and, by 

 analogy from other tissues, this may be true for other 

 electrolytes as well (19, 211). There is still much to 

 learn about the distribution of water and electrolytes 

 and their importance in metabolism (92, 221), but 

 it is apparent that neural structures have a role in 

 determining the distribution of certain ions which 

 are invoked in neuronal function. 



Other solutes beside those just discussed are also 

 present in cerebral water. With the exception of 

 amino acids, most are present in trace or relatively 

 small amounts. Some of them are considered lielow 

 (table 4). 



.Snliils. The solids of the brain account for onh .1 

 small percentage of the total mass, averaging 16 per 

 ceni in gray matter and about twice that amount in 

 white (figure 1). The two principal constituents of 

 the solids fraction are proteins and lipids, the residuum 

 accounting for only 1 ;, to 20 per cent of the dry 

 weight. Gray-matter solids predominate in proteins 

 (about half the <h\ weight), whereas almost two- 

 thirds of white-matter solids are lipids. 



lipids. Cerebral lipids are not so much peculiar in 

 type as in concentration; brain, in white matter 

 particularly, is higher in complex lipids than any 

 other oil;. m. Cerebral tissue is further distinguished 





