DISEASES OE NEBVES 255 



fibers run downward in tlie lateral columns of the spinal cord, 

 a great many of them becoming connected with the large mul- 

 tipolar cells in the inferior horns of gray matter ; from here 

 the motor impulse is transmitted by the inferior root, which, 

 together with the superior root, the sensory one, constitutes the 

 spinal nerve leading to the sMn, muscles or viscera. 



Into what two large divisions may the motor tract he subdi- 

 vided ? 



1. The cerebro-spinal tract— that is, the one beginning in 

 the motor centers of the cerebrum and ending, so to speak, in 

 the large multipolar cells of the inferior gray horn. 3. The 

 'peripheral tract — that is, the one beginning with the inferior 

 and superior root and extending to the periphery — that is, the 

 muscles. 



What are the causes of paralysis ? 



Peripheral paralyses are usually due to some traumatism, 

 as contusions, lacerations, stretching; cerebral and spinal 

 paralyses more generally are due to cerebral and spinal 



What general symptoms does a paralyzed muscle exhibit? 



Voluntary contractions are .either impaired (paresis) or 

 impossible (paralysis). As a rule, the paralyzed muscle is 

 flabby and does not oppose passive movements. But the par- 

 alyzed muscle may be reflexly stimulated and appear in a state 

 of continuous contraction. Usually the paralyzed muscle 

 atrophies more or less rapidly. 



What deduction can you make from reflex movements taking 

 place through the spinal cord ? 

 By artificially producing reflex movements of muscles 

 : one can determine the condition of the various segments of 

 the spinal cord. 



