what is a extensor
extensor a muscle that extends or straightens a limb. extensor a muscle, contraction of which tends to straighten or dorsiflex a joint; the antagonist of a flexor extensor [L.] any muscle that extends a joint. See Table 13 for list of all muscles. crossed extensor reflex. see crossed extensor reflex. extensor postural thrust a postural reflex reaction tested in small animals by lifting the patient off the ground, then lowering it to see whether the hindlegs are extended to make contact and support weight and several short steps are taken to maintain posture.