[Physical diagnosis--plantar reflex].

On stimulation of the plantar surface an extensor response of the toes (especially the big toe; Babinski sign) indicates a disorder of the corticospinal system: disinhibition of reflex activity causes the big toe to be recruited into the synergistic flexion reflex of the leg (toe extensors are flexors in a physiological sense). Proper assessment of the plantar reflex therefore involves not only rating toe movements, but also observing simultaneous contraction of flexor muscles in the thigh. Disregard of the association with the flexion synergy has given rise to some misunderstandings.