CHAPTEB X( IX 



FUNCTIONS <»!•' THE CEREBELLUM 



In our discussion of reflex action we have so Ear considered only tl, 

 receptors coming from the exterior of the body, although we have r< 

 aized thai a considerable Dumber of the afferenl aerve roots contain fibers 

 coming from receptors situated in the muscles, the tendons and the joints, 

 and called proprioceptors because they respond not to changes in the 

 environmenl but to alterations in the body itself. We ha o that the 



proprioceptors consisl structurally of muscle spindles and of the ne 

 endings in the tendons and ligaments and synovial membranes. They are 

 receptors that are attuned to respond to differences in tension caused either 

 by bulging of the muscles or by stretching of the fibers of tendons a 

 Ligaments. 



The impulses are transmitted in the spinal cord, either by the posterior 

 columns <>r by the lateral cerebellar tracts. Those traveling by th>' pos- 

 terior columns are sent mainly to the cerebral cortex of the opposite side, 

 whereas those in the cerebellar tracts enter the cerebellum by the inferior 

 peduncles of the same side. The cerebral impulses conned with ne 

 which transmit the impulse back again to the cerebellum of the oppos I 

 side, so that ultimately the cerebellar cortex is connected with the spinal 

 cord "i' tin- same Bide either directly or indirectly through the cerebral 

 cortex. These anatomical facts indicate in ;i general way that we may 



expect the function of the cerebellum tn he that of the chief nerv niter 



concerned in the integration of the proprioceptive impulses originated by 

 the condition of contraction or relaxation of the different groups 

 muscles in the body, and by the amount of tension existing in the var 

 tendons, ligaments and other membranes surrounding t lie joints. 



Experimental investigation has justified thes tions The re- 



moval of the entire cerebellum— an operation which has usually been 

 performed <m birds, particularly pigeons, because of the ease with which 

 it can be done in these animals— leads immediately to a condition in which 

 muscular activity is entirely uncontrolled. A pigeon after this operation 



flies aboul in an hit rdinate way. turning summersaults, dashing i 1 - 



against the walls of its chamber, and ultimately after constanl futile mo 

 ments, exhausting itself, [f one cerebellar lobe i^ removed, the body when 

 at re>t is curved toward the side of the lesion, and the movements 



