SECTION IX 

 TROPHIC FUNCTIONS OF THE CORD 



THE reflexes which are excited by painful or nocuous stimuli 

 must be regarded as prepotent in that their inhibitory effect on 

 other reflexes is more marked than that produced by any other 

 quality of stimulus. In the struggle for existence the reaction to 

 nocuous stimuli must predominate over those due to any other kind, 

 since it is essential for the survival of the animal that the stimulus 

 should be removed or avoided, so that the animal should escape from 

 its injurious effects. 



It is natural therefore that after complete section of the afferent 

 nerves from any part of the surface of the body there should be a 

 tendency to trophic disturbances, such as the formation of ulcers, &c. 

 Such ulceration is frequently observed in patients suffering from 

 spinal disease. After section of the first division of the fifth nerve 

 ulceration of the cornea is often produced. These effects are, however, 

 merely due to the absence of the normal protective reactions of the part, 

 and can be prevented by scrupulous cleanliness and protection of the 

 apaesthetic part from all possible injuries. There are other trophic 

 effects caused by nerve lesions which cannot be ascribed to the mere 

 absence of protective reflexes. Thus inflammation of the posterior 

 root ganglia often sets up herpes zoster, or ' shingles,' in the region of 

 cutaneous distribution of the corresponding sensory nerve. Changes 

 in the skin (' glossy skin ') nails and hair are often seen after irritative 

 injuries of nerves to the part. Section of a motor nerve causes rapid 

 changes in the skeletal muscles supplied, which become smaller and 

 after months or years may disappear altogether, being replaced by 

 connective tissue. The changes in the excitability of the muscles 

 produced under these circumstances have already been described. 



It seems that the nutrition of a tissue is determined by its activity, 

 and this in turn is-under the control of some nerve path. Section of the 

 nerve path, by cutting away the impulses which normally maintain the 

 activity of the part, must at the same time seriously affect its nutrition. 

 Thus the muscles which, though striated, are not so immediately 

 under the control of the central nervous system, such as the sphincter 

 ani, do not undergo degeneration after section of their nerves, or 



after extirpation of the lower part of the spinal cord. 



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