SPINAL CORD. 



477 



rior division which goes to the anterior part ; each division contains 

 fibers from both roots. 



Functions of the Spinal Cord. The functions of the 

 spinal cord are of two kinds : 1. A conductor of impulses, by 

 virtue of the fibrous nervous matter which it contains ; and 2. 

 A nerve-center, by virtue of its nerve-cells. 



As a Conductor of Impulses. The spinal cord is the principal 

 channel through which all 

 impulses from the trunk 

 and the extremities pass 

 to the brain, and all im- 

 pulses to the trunk and 

 extremities pass from the 

 brain. If through disease 

 or injury the cord is disor- 

 ganized at any point, all 

 power to produce volun- 

 tary motion in the parts 

 below the injury is lost, 

 and conscious sensation in 

 these parts is from that 

 moment abolished. The 

 cord therefore acts as a 

 conductor of impulses, 

 both motor and sensory, 

 between the brain and the 

 trunk and extremities ; the 

 different kinds of impulse 

 follow different paths in 

 the cord. 



Conducting-paths in the 

 Cord. The paths by which 

 voluntary motor impulses 

 traverse the cord are fairly 

 well ascertained. These im- 

 pulses originate in the pyr- 

 amidal cells of the cerebral 



cortex, and pass through the 

 pyramids in the medulla, 

 crossing principally at the 



FIG. 277. Schema showing pathway of the 

 sensory impulses. On the left side, A*?, &, repre- 

 sent afferent spinal nerve-fibers ; C, an afferent 

 cranial nerve-fiber. This fiber in each case ter- 

 minates near a central cell, the neuron of which 



V~ & I"-* *~*y""-*J crosses the middle line and ends in the opposite 



deciissation Ot the pyra- hemisphere (van Gehuchten). 

 mids, and to a less degree 



in the upper part of the cord, to the opposite side, whence they 

 follow the course of the pyramidal tracts, direct and crossed, arbo- 

 rizing around the cells of the anterior cornua ; from which the 

 anterior roots arise to be distributed to the muscles. 



The course pursued by the sensory impulses (Fig. 277) is not 



