The Support Reaction in Spinal Animals

Abstract

Rademaker observed what he called the “Stütz” reaction in decerebellate dogs. Pressure against the pads of the toes, simulating that exerted by the floor against the foot, causes contraction of the muscles of the entire leg in such a way as to convert it into a prop or Stütz. This reflex is a very important factor in reflex standing. Since its discovery by Rademaker, 1 it has been described in detail by Schoen 2 and Pritchard. 3

Pressure against the pads of the foot stimulates the nerve endings in the skin (exteroceptive) and by stretching the muscles which flex the toes and extend the ankle it also stimulates the nerve endings in these muscles (proprioceptive). Both of these types of stimuli take part in producing the reflex. According to Schoen it occurs after section of all of the nerves to the skin of the foot and must then be purely proprioceptive. In decerebellate animals it can be evoked by touching the pads of the toes, which shows that it can be elicited by tactile stimuli acting alone.

It is most easily studied in animals in which all of the brain in front of the thalamus has been removed. Schoen was unable to demonstrate it in spinal animals except that there was some indication of its presence in decapitate animals when the neck reflex was exerting an influence favorable to extensor tonus.

We have observed the support reaction in decapitate dogs, decapitate cats, and in both acute and chronic low spinal cats. In acute experiments with decapitate and low spinal preparations the reflex can best be demonstrated when reinforced by extraneous stimuli. Pinching the tip of the tail will often furnish the required reinforcement.