CHAPTER VI 



THE GENERAL PHYSIOLOGY OF THE NERVOUS 



SYSTEM 



THE functions of the body are generally effected by chemical 

 changes within its protoplasm. These chemical changes in the 

 aggregate we term "metabolism" and they generally involve a 

 rather slow interchange of the chemical substances of food and 

 waste materials between the cytoplasm and the lymph which 

 surrounds the cells and between the cytoplasm and the proto- 

 plasm of the nucleus (karyoplasm). The rate of metabolism is 

 dependent upon many factors, one of which is the time required 

 for the passage of soluble substances through the cell membrane 

 and through the nuclear membrane which separates the cyto- 

 plasm from the karyoplasm. 



In the nerve-cells both of these sorts of chemical interchange 

 are facilitated by the form and internal structure of the cell. 

 As we have already seen (p. 41), the widely branching dendrites 

 present a large surface for the absorption of food materials from 

 the surrounding lymph and the elimination of waste. The 

 specific nervous functions involve the consumption of living sub- 

 stance, both in the cell body and in the nerve-fibers. This is 

 in part an oxidation process, and this phase of the activity can 

 be roughly measured by the amount of carbon dioxid eliminated. 

 Until very recently it was not possible to secure any evidence of 

 CO2 production in nerve-fibers; in view of this and of the further 

 fact that nerve-fibers seem to be less susceptible to fatigue than 

 nerve-cells and synapses, many physiologists assumed that 

 nervous conduction is not a chemical process, but perhaps some 

 sort of molecular vibration. The conduction of a nervous im- 

 pulse through a living nerve-fiber is accompanied by an electric 

 change, the so-called negative variation, which by some physi- 

 ologists has been identified with the nervous impulse itself. 

 This and other complicated theories of nervous transmission 



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