90 



THE NERVOUS SYSTEM 



lined is on the basis of the neurone theory; should the nerve-cells be 

 proved to be only trophic centers, material changes would of necessity 

 result in our notions as to the mode of action of the spinal cord and 

 especially regarding its relations to the spinal nerves. 



The anterior roots, mostly efferent in action, receive their impulses from 

 many-branched neurones situated in the gray matter of the cord, and 

 more usually in the anterior (ventral) horns of this gray matter. In the 

 most complex animals each ventral root is made up by combination of a 

 row of rootlets, and each rootlet represents in miniature the whole root, 

 the spinal cells in connection with them coming from slightly different 

 levels of the cord. By this arrangement it is brought about that no root 

 or rootlet represents a single muscle, but rather in part all the muscles of 

 a functional group. Each muscle, moreover, is thus innervated from 



Posterior root, 

 f.p 

 \ 



FIG. 46 



Posterior 



median Column Posterior Column of 

 septum, of Goll. column. Burdach. 



/ Posterior 

 / horn. 



Anterior long, 

 fissure. 



\ A nterior ground 



bundle. 

 Direct pyramidal 

 column (T'urck). 



Direct cerebellar 

 column. 

 Crossed pyram- 

 idal column. 



Column of 

 Clark. 



Mixed lateral 

 column. 



Ascending antero- 

 - lateral column 



(Gowers). 



"*-.. Anterior com- 

 missure. 



Descending ante- 

 rolateral area. 



Diagram of the physiological structure of the spinal cord. 



and H. Hackel.) 



(Ziehen, von Bardeleben, 



several (three or four) segments. In some parts of the cord, notably those 

 representing the neck- and limb-muscles, the anterior root-cells are dis- 

 tinctly collected into groups, each group probably innervating collectively 

 a group of muscles. The largest motor cells probably control cross- 

 striated (skeletal) muscles, while the smaller ones may innervate the 

 muscle-fibers ("unstriated") of the bloodvessels and of the viscera. 

 Cells for flexion and cells for extension of a joint, for example, seem to 

 lie intermingled in the same segments of gray matter. Both sorts of 

 cells are probably (Sherrington) actuated at every movement of the joint, 

 flexor or extensor, one set being stimulated to actuate and the other to 

 inhibit. Sherrington notes the discovery by Golgi that from the neur- 

 axones of some spinal efferent root-cells "side-fibers" are given near their 

 origins. These may conduct efferently into the axone, but for what 

 purpose is not known; von Lenhossek terms them axo-d end rites. 



