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HANDBOOK OF PHYSIOLOGY — NEUROPHYSIOLOGY III 



Salt deficiency causes nervous dysfunction, not only 

 in acute deprivation but also under chronic conditions 

 producing; low concentration of salt in the blood. 

 1 1\ pochlorcmia is associated with headache, dizziness, 

 tremor, hyperreflexia, hyperhydrosis, nervousness, 

 apprehension, restlessness, insomnia, loss of *pcp' 

 and strength, depression, personality changes, and 

 anxiety (228). 



Calcium 



Extracellular calcium is necessary for the preserva- 

 tion of the selective permeability of cell membranes, 

 the ease with which sodium and potassium cross the 

 nerve membrane being reduced by increased calcium 

 level (131, p. 451)- Accordingly, lowering of calcium 

 concentration results in greater excitability and a 

 tendency to repetitive discharges on stimulation. 

 Tetany develops in rats on a low : calcium and high 

 phosphorus diet, deficient in vitamin D and resulting 

 in rickets with low plasma calcium (26, 244, 248). In 

 man tetany occurs when there is a low concentration 

 of ionized plasma calcium. Primary calcium deficiency 

 in man is probably very rare (253). Tetany has also 

 lii-cn reported during; periods of semistarvation (232) 

 and spontaneous muscle cramps have been observed 

 in undernourished children (221). 



Magnesium 



Magnesium is necessary as activator of various 

 enzyme systems, including choline acetylase (135). 

 Perhaps the first demonstration of neurophysiological 

 relevance of magnesium was the discovery of the 

 depressing effect of magnesium salts on the nervous 

 svstcm (170, 206). Magnesium concentration of 5 mg 

 per 100 ml of serum produces mild sedation, while 

 profound coma results when the concentration reaches 

 the level of 18 to 21 mg per loo ml (188). The efTects 

 of tlii-- metal on muscular activity ma) be explained 

 .iv .1 blocking at the neuromuscular junction (107). 

 The narcotic effects oi magnesium on the central 

 nervous system are abolished b) the injection of 

 calcium salts ' 1 71 ). 



Nutritional deflcienc) of magnesium causes cattle 

 to become nervous and restless, and to lose appetite. 

 In .1 more advanced state the) develop convulsions 

 and coma, and die (58, 247) In rats the main signs 

 are increased nervous excitabilit) and convulsions, 

 followed b) deal 1 1 f 1 |6, 1 17) Similar symptoms were 

 orted in the dog (109; cf. aUi> 21, 2 \, 99 Barron 

 iii// ( in' found magnesium dehcienc) in the rat and 



the rabbit to result in chromatolysis and degeneration 

 of the Purkinje cells of the cerebellum. 



Effects of magnesium deficiency on nervous func- 

 tions in man are still not well established. In 1944 

 Miller (172) described a case of tetany due to defi- 

 ciency of magnesium, and the name of "magnesium 

 tetany' is found in the literature. Recently Flink and 

 his associates (76) reported finding tremor and delir- 

 ium in patients who received parenteral fluids for a 

 long time and in chronic alcoholics; in both groups 

 low levels of serum magnesium were found and the 

 administration of magnesium salts gave relief. How- 

 ever, a recent paper (74) contains a description of two 

 cases of magnesium deficiency experimentally pro- 

 duced in man, with no mention of neurologic or 

 psychiatric manifestations. 



An interesting aspect of the effects of magnesium 

 on the nervous system is the antagonistic action of 

 potassium. Potassium salts relieve the narcotic effect 

 of magnesium, while the administration of magnesium 

 lowers the serum level of potassium (250, -ji)- 



Manganese 



Manganese is known to act as an activator of some 

 enzyme systems and is considered a dietary essential 

 for higher animals and man. Manganese deficienc) 

 produces alterations of growth, bone development and 

 reproduction. In some animal species certain altera- 

 tions of nervous function arc noted. In the rat there U 

 loss of equilibrium and incoordination of movements 

 (241 ). In the pig, weakness of the legs has Seen noted 

 (129, 174) and more recently it was reported (213) 

 that sows maintained on a manganese-deficient diet 

 gave birth to small, weak pigs unable to stand or to 

 walk normally, 



Iodine 



Iodine is the onl) trace element that is essential 

 for the proper functioning of an endocrine gland, the 

 thyroid. Deficiency of dietary iodine results in an 

 impaired production of thyroid hormone. I ncor- 

 rected hypothyroidism results in retarded mental 

 development of the child, and in mental dullness and 

 apalhv in the adult. Neurophysiolinjically, the de- 

 pressed function of the central nervous system is 

 manifested in the impaired abilit) to form condi- 

 tioned reflexes (83). However, impaired intelligence 

 is mil .1 necessar) concomitant oi acquired hypo- 

 thyroidism 1 1 77). 



