A comparison of flexor and extensor reflexes of muscular origin.

Whereas extensor muscles of decerebrate mammalian preparations usually present both phasic and tonic reflex contraction to stretch (Liddell & Sherrington, 1925), flexor muscles present phasic stretch reflexes only (Asayama, 1916). Under anaesthesia or during spinal shock (Creed, Denny-Brown, Eccles, Liddell & Sherrington, 1932, p. 51), tonic stretch reflexes are lost while phasic responses are maintained. Extensor and flexor muscles then respond in a similar way to applied stretch. The present research was undertaken with the purpose of identifying the processes responsible for this difference between flexor and extensor pathways. This appeared to be a convenient way of approaching an understanding of the central events which underlie the development of sustained reflex responses.