MECHANISMS OF INTERLIMB REFLEXES IN CAT

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Abstract
Certain aspects of the mechanisms mediating long spinal reflex relations between hindlimbs and forelimbs have been examined. Partial sections of the spinal cord demonstrate that ascending connections necessary for the transmission of this interlimb activity are part of a diffusely projecting spinal system. However, ascending pathways localized in the dorsal quadrants are of greater importance than those within the ventral quadrants, and uncrossed tracts are more essential than crossed connections. Ascending interlimb reflex responses obtained in decerebrate cats are eliminated by spinal transection through the atlanto-occipital membrane. This indicates that the reflex activity conducted in ascending propriospinal systems is insuf- ficient to evoke reflex responses as compared with the activity which is apparently channeled through a supraspinal loop before reentering the spinal cord. Cerebellectomy reduces the effectiveness of this re-entry loop but does not abolish it. Spinal projections to the brain-stem reticular formation are evidently sufficient to maintain the basic pattern of ascending interlimb reflexes.