CHAPTER XLVII 



FUNCTIONS OF THE SPINAL CORD 



THE functions of the spinal cord fall into two categories : functions 

 of the grey matter, which consist in the reflection of afferent im- 

 pulses, and their conversion into efferent impulses (reflex action) ; and 

 functions of the white matter, which are those of conduction. 



The Cord as an Organ of Conduction. 



We have studied at some length the various paths in the white 

 matter, and so we have the materials at hand for recapitulating the 

 main facts in connection with the physiological aspect of the problem. 



Complete section of the spinal cord in animals, and diseases or 

 injuries of the cord or spinal canal in man, which practically cut the 

 cord in two, lead to certain histological changes of a degenerative 

 nature, which we have already studied, and to physiological results, 

 which are briefly (1) paralysis, both motor and sensory, of the parts 

 of the body supplied by spinal nerves which originate below the 

 point of injury; and (2) increased reflex irritability of the same 

 parts, the reason for which we shall study immediately. 



Hemisection of the cord leads to degenerative changes on the 

 same side of the cord, and loss of motion and sensation on the same 

 side of the body below the lesion (see p. 619). 



The main motor path in the cord from the brain is the pyramidal 

 tract ; the anatomy of this tract is described in Chapters XLII. to 

 XLVL, and we need do no more here than remind the reader that it 

 originates from the pyramidal cells of the cortex of the opposite 

 cerebral hemisphere, and that the principal decussation occurs at the 

 lower part of the bulb. 



The sensory tracts are more complex, on account of the numerous 

 cell-stations on their course. The path for tactile and muscular 

 sense impressions is up the posterior columns to the nucleus gracilis 

 and nucleus cuneatus ; thence by the internal arcuate fibres and fillet 



