THE FUNCTIONS OF THE CEREBELLUM 



401 



The cerebellum is a receiving station, not only for impulses which arise in 

 the skin and eyes, i.e. on the surface, of the body, but especially for those 

 which have been denned as proprioceptive and originate either in the muscles 

 and tendons or in the labyrinth. Activity of this apparatus is roused as a rule 

 by the movement of the organism itself, and is only a secondary result of the 

 environmental stimulation which provoked the original movement. By its 

 efferent tracts starting in the roof- and paracerebellar nuclei, the cerebellum 

 is able to affect the musculature of the same side of the body by a direct 

 influence on the anterior horns. It also enters to a much greater extent into 

 relation with the opposite cerebral hemi- 

 spheres, so that it is in a position to 

 control or modify the activity of these, 

 whether excited on their ^ sensory or on 

 their motor sides. 



STIMULATION OF THE CEREBEL- 

 LUM. It was first shown by Ferrier 

 that movements of the same side of 

 the body can be excited by stimulation 

 either of the cerebellar hemispheres or 

 of the superior vermis. These results 

 have been confirmed by subsequent 

 observers, and point to each half of the 

 cerebellum being connected functionally 

 with the skeletal muscular apparatus of 

 the corresponding side of the body. 

 The cortex cerebelli is not excited 

 with ease. To evoke movements much 

 stronger stimuli are necessary than 

 e.g. for the excitation of the motor area, 

 of the cerebral cortex. This again 

 is in accordance with what we should 

 expect from. the anatomy of the organ, 



knowing as we do that the cortex is an FIG. 202. Diagram of afferent and efferent 



end-station for a number of afferent ff?fgS. } 



paths, but has no direct efferent paths OT, optic thalamus ; RN, red nucleus ; 



from it to the lower motor mechanisms 

 of the cord. On the other hand, move- 

 ments are excited by minimal stimuli from the intrinsic nuclei of the 

 cerebellum. 



As a result of his experiments Horsley concluded that the cortex 

 cerebelli must be regarded as an afferent receptive centre from which axons 

 pass to the ventrally placed efferent nuclei, viz. the nuclei dentati, fastigii, 

 emboliformes, as well as Deiters' nuclei. Whereas excitation of the roof nuclei 

 produces more especially movements of the eyes and head, the paracere- 

 bellar (e.g. Deiters' nucleus) are responsible more especially for the move- 

 ments of the trunk and limbs. The movements of the body which are thus 



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