SPINAL CORD. 109 



beyond the ganglion does not degenerate. The anterior root can- 

 not, however, be divided at any point beyond its emergence without 

 centrifugal degeneration of the fibres (Fig. 30). The regeneration 

 takes place slowly if the continuity of the nerve is at once restored, 

 and may even follow after the nerve has degenerated for some months 

 and a complete loss of function has affected the part supplied by 

 it. The fact that the axis-cylinders are restored only in this way 

 is of interest, as showing the influence of the trophic centres on 

 the nerve-growth. 



What are the functions of the spinal cord ? 



(1) The conduction of impulses from the nerves to the brain 

 and from brain to nerves, and (2) the origination of action in 

 response to stimuli from the periphery i. e. reflex action. 



Explain the action of the cord as a conductor of nervous impulses. 

 Than by the spinal cord there is practically no other nervous 

 communication between the brain and the musculo-cutaneous sys- 

 tem ; hence through it must come all the nerve-impulses which 

 pass to or from the brain. In other words, every sensory impulse 

 that is felt and every motion that is willed, perception and volition 

 being attributes of the brain, must be conducted through the nerve- 

 fibres of the spinal cord to the brain, and vice versa. No better illus- 

 tration need be used than the abolition of both motor and sensory 

 function which follows a cerebral apoplexy : the nerve-centre being 

 destroyed, voluntary action and perception of sensation are lost, 

 and yet the reflex response is prompt, showing that the brain- 

 function is necessary in the chain of phenomena. Again, the 

 same paralysis follows the section of the cord, and we must 

 acknowledge their mutual dependence. 



Does the gray substance act as conductor? 



No, not when directly stimulated. The conducting fibres seem 

 to be in the white columns, and each portion contains fibres which 

 always conduct the same kind of impression. 



What is the course of sensory impulses in the spinal cord ? 



This is somewhat problematical, but certainly these impulses 

 enter the cord by the posterior nerve-roots. The fibres conducting 

 them break up to form Gerlach's network, and cross to the opposite 

 side of the cord through the gray commissure. It is probable that 

 after decussating the fibres communicate with multipolar cells, and 



