Normal plantar response: integration of flexor and extensor reflex components

Abstract

An electromyographic study of the skin reflexes of the foot was carried out on 25 neurologically healthy subjects. Reflexes were elicited by painful stimuli consisting of repetitive electric shocks, 1 msec duration, 500/sec frequency, delivered over a 20 msec period to the plantar surface of the foot. Only reflexes of shorter latency than 100 msec were studied as these were presumed to be of purely spinal origin. Upon stimulation of the hollow of the foot the shortest latency recorded in the short hallux flexor and extensor was 55 msec. As stimulus was shifted from the hollow of the foot to the hallux ball, hallux response changed from plantar to dorsal flexion, while a shift from the hollow of the foot to the plantar surface of the heel produced a change from dorsal to plantar flexion. As stimulation was shifted from the medial to the lateral side of the sole, ankle movement changed from supination to pronation. The coordinated reflex movement simulated a defense mechanism removing the skin area from the noxious stimulus. Excessively strong stimulation produces pure flexor reflex as seen in pathological cases. Each individual has a basic reflex pattern. Deviations mirror changes in cerebral influence on the spinal centre. The organization of this suprasegmental control over the reflex centre differs in individuals and is exerted via more than one path.