NERVE 91 



and the tonic condition of the muscles is increased because 

 the impulses from the vestibulo-cerebellar arc (p. 121), 

 which increase the tonic action of the spinal arcs, are 

 no longer held in check by impulses from the cere- 

 brum. 



When the cerebellar arc is thrown out of action one of 

 the most marked features is a loss of muscular tone. 



Trophic Influence of the Cord. 



The spinal cord presides over the nutrition of the 

 muscles, which are directly supplied by fibres coming from 

 cells in the cord. When disease destroys the cells of the 

 anterior horn, the muscles atrophy and degenerate. 



Injury of the cells connected with the outgoing visceral 

 fibres does not lead to the same atrophy and degeneration 

 of the visceral muscles supplied. Apparently the post- 

 ganglionic neurons survive degeneration of the pre-ganglionic 

 fibres (p. 76), and are able to maintain the nutrition of the 

 structures supplied. Even after the post-ganglionic fibres 

 have degenerated, it is probable that the terminal nerve 

 plexuses, which in the intestine at least act as local reflex 

 centres, survive and are capable of presiding over the 

 nutrition of the tissue. 



Certain facts seem to indicate that the inofoiuCT fibres with 

 their cells in the ganglion upon the posterior root are 

 connected with the nutrition of the structures from which 

 they pass. Thus shingles — herpes zoster, an outbreak of 

 vesicles along the distribution of a cutaneous nerve — has 

 been found to be associated with inflammatory conditions of 

 the ganglia (p. 93). 



Relationship of Nerve Cells to Muscles. 



The Nissl's degeneration (p. 77) of special groups of 

 cells in the anterior horn of grey matter after amputation of 

 the leg at different levels seems to indicate that the various 

 groups of cells have definite connections with individual 

 muscles (see fig. 40). 



