EFFERENT PATHS AND REFLEX ARCS 



327 



of decerebrated dogs, which Sherrington (1906) clearly showed to be a proprio- 

 ceptive reflex that under normal conditions serves to keep the limbs from bend- 

 ing under the weight of the body, is apparently dependent upon the integrity of 

 the cerebello-rubro-spinal path. Weed showed that removal of the cerebellum, 

 section of the superior cerebellar peduncles, or transection of the mesencephalon 

 below the level of the red nucleus obliterated or greatly decreased this rigidity. 



Rubrospinal tract ^ 

 Rubroreticular tract 



From frontal lobe and corpus striatum 

 " Thalamus 



I Red nucleus 



Brachium conjunctivum 

 ' Dentate nucleus 



Pons 

 Rubrospinal tract 



J Medulla oblongata 



u 



Reticulospinal tract 



Spinal cord 



Fig. 243. Diagram showing the connections of the red nucleus: A, Ventral tegmental 

 decussation; B, decussation of the brachium conjunctivum; C and D, descending fibers from bra- 

 chium conjunctivum, before and after its decussation respectively. 



On the other hand, stimulation of the area occupied by the red nucleus on the 

 cut surface of the mesencephalon in decerebrated dogs increased the rigidity. 



IMPORTANT REFLEX ARCS 



We have considered the afferent paths leading to the cerebral cortex and to 

 the cerebellum as well as the efferent channels which conduct impulses from these 

 centers to the skeletal musculature. But there are many more direct paths 

 by which impulses may travel from receptor to effector, and these are known as 

 reflex arcs. It will be worth while to review briefly a few of the more important 

 of these rather direct receptor to effector circuits. 



