THE CROSSED EXTENSOR REFLEX IN DEAFFERENTED MUSCLE

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Abstract
At periods varying from 14 to 35 days after transec-tion of the dorsal roots of the right L VI, VII, S I, II, and III nerves, cats were decerebrated and kymograph records made of the crossed extensor reflexes in the right gastrocnemius. In animals decerebrated by the transection method the tonicity of the reflex depended on the height at which the brain stem was cut across. After transection at the upper border of the mesen-cephalon the reflex was atonic; and relaxation followed abruptly the cessation of the stimulus. But if the transection was made at or near the upper border of the pons, the deafferented gastrocnemius responded to stimulation of the opposite popliteal nerve by a prolonged tonic contraction. It is possible to obtain from one and the same deafferented muscle an atonic crossed extensor reflex after high decerebration and a few minutes later a tonic crossed extensor reflex after a second transection of the brain stem at a lower level.

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