550 TEXT-BOOK OF PHYSIOLOGY 



below the section, while electric stimulation of the peripheral end of the 

 isolated crossed pyramidal tract is followed by marked characteristic move- 

 ments of the muscles. Similar results follow division of the pyramidal trac^ 

 in any part of its course from the cerebral cortex downward. Electrid 

 stimulation of the cortical cells which give origin to the pyramidal tract ig 

 also followed by contraction of the muscles of the opposite side, while theii 

 destruction is attended by paralysis of the same muscles. As the nutrition oi 

 the fibers is governed by the cells, it follows that when the axon is separated 

 from its cell-body it degenerates. It has been found that a lesion of the 

 pyramidal tract in any part of its course is followed by descending degenera- 

 tion, which is taken in evidence that it conducts nerve impulses from above 

 downward. Thus experimental investigation and pathologic observation are 

 in accord in the view that physiologically these nerve-fibers are the pathways 

 for the transmission of motor or volitional impulses from the encephalon 

 to the spinal cord. 



The pyramidal tracts are also the conductors of the nerve impulses dis- 

 charged by the cells of the cerebrum during the occurrence of the affective 

 or emotional states, that excite to activity the lower nerve centers; those that 

 give origin to the autonomic nerve fibers which excite to activity the epithelium 

 of glands, the non-striated muscles in the walls of the blood-vessels and viscera. 



