Responses of Higher Animals: The Nervous System - 463 



CEREBRUM 



MAIN SENSORY 

 PATH TO 

 CEREBRUM— 



THALAMUS 



CEREBELLUM 



FROM 

 LABYRINTH 

 TO 

 CEREBELLUM 



Fig. 25-14. Some main conduction 

 pathways in the brain and spinal cord 

 of man. Although the sensory pathways 

 are shown on the left and motor path 

 on the right in this diagram, actually 

 both types of pathways are bilateral. 



MAIN SENSORY PATH 

 TO CEREBRUM 



MOTOR PATH FROM 



CEREBELLUM TO 



MUSCLES 



FROM 

 LOCAL 

 RECEPTORS 



rons may be exceeding large indeed (see Fig. 

 25-14). 



The spinal cord serves as the conduction 

 pathway for impulses traveling upward to 

 the higher centers and downward from the 

 higher centers to effectors situated below the 

 level of the head. In the spinal cord, more- 

 over, impulses of different origins and desti- 

 nations tend to follow certain rather specific 

 main fiber tracts. 



Main Sensory Tracts. The association neu- 

 rons that carry impulses from the pain and 

 temperature receptors, cross over imme- 



TO SKELETAL 

 MUSCLE 



diately to the opposite side of the cord and 

 then pass upward toward the brain. But im- 

 pulses from the touch and pressure receptors, 

 and impulses from the proprioceptors of the 

 muscles and tendons, do not cross over, but 

 pass upward in the cord on the same side, 

 that is, on the side where the stimulated re- 

 ceptors are located. 



The localization of the main sensory tracts 

 is clearly demonstrated in cases of unilateral 

 injuries of the spinal cord. If only the right 

 side of the spinal cord is crushed or damaged, 

 the subject suffers a loss of "muscle sense" 



