The effect of knee joint afferent discharge on transmission in flexion reflex pathways in decerebrate cats.

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Abstract
Changes in excitability of reflex arcs mediating flexion withdrawal and crossed extensor reflexes were examined in decerebrate cats. The excitability of flexion withdrawal and crossed extensor reflexes was modulated by knee joint position. Flexion withdrawal reflexes were most easily elicited when the knee was extended, and crossed extensor reflexes were most easily elicited when the knee was flexed. The modulation of transmission was not confined to reflex pathways to muscles acting at the knee but also included pathways to muscles acting at the hip and ankle, and pathways to muscles in the contralateral limb. The changing excitability of reflex pathways caused by movement of the knee joint was unrelated to the stretch applied to muscles acting at the knee, and to cutaneous afferent discharge. Modulation of reflex excitability by joint movement was totally abolished by local anesthesia of the knee joint in an otherwise intact limb. Transmission in flexion reflex pathways are apparently inhibited by knee joint afferent discharge.