232 



HUMAN PHYSIOLOGY 



CHAP. 



Cerebrum 



of the cerebrum. It extends down into every fissure 

 and up over every convolution, and in this way the area 

 of the gray matter is increased many fold. 



The cells of the cerebrum are also grouped into defi- 

 nite centers, each having its own work to do and never 

 attempting anything else. The centers may be said 



to belong to one of three 

 kinds ; namely, sensory, 

 motor, or association. The 

 sensory areas are those 

 parts of the cerebrum to 

 which impressions are car- 

 ried by the sensory nerves. 

 We notice in the diagram 

 that a part of the occipital 

 lobe is the center for sight, 

 the temporal for taste, 

 smell, and hearing, and the 

 upper and inner part of 

 the parietal for touch. The 

 motor areas have to do 

 with sending messages out over efferent nerves to the 

 different voluntary muscles of the body. We see in 

 the diagram that the parietal and a small part of the 

 frontal lobes constitute the motor area. If any cells of 

 the motor area are stimulated with electricity, a definite 

 muscular response will always follow. By such experi- 

 ments the use of every part of the motor area has been 

 fully mapped out. The association areas are neither 

 motor nor sensory, but are very highly developed in man, 



FIG. 126. Showing the lobes of the 

 brain and their functions (Zuppke). 



