266 



STUDIES IN PHYSIOLOGY 



brain. Not until the message reaches these cells am I con- 

 scious that I have been burned. Fortunately, however, my 

 hand has already been removed from danger. 



JVoter ct/t of 



,.-' cerebral cortex 



>''~,~ 'Ce// of cortex of 

 <" cfrefira/n 



ffferent newe- - - 

 from cerebrum 



Cere0e//(/m 



Jfferentrterre 



to cerebrum 



Afferent nerve to 

 cere6e//un? 



Afferent rtery& 

 fro/n sfl/na/ co ' 



r - -Afferent r?erre 

 to spjra/coraf 



FIG. 123. Diagram to illustrate Cells and Afferent, Efferent, and Connect- 

 ing Fibers of Brain and Spinal Cord. 



Many other activities of the body, as we shall soon learn, 

 are carried on in a reflex manner similar to that already 

 described, and are executed entirely without our conscious 

 effort. 



4. THE SYMPATHETIC NERVOUS SYSTEM 



Anatomy. Closely associated with the spinal nerves is 

 the sympathetic nervous system. It consists of a number of 

 gray ganglia, the nerve cells of which are connected by gray 

 nerve fibers (fibers without the medullary sheath). Most of 

 the sympathetic ganglia are strung together in two parallel 

 chains that extend along either side of the spinal column 



