LOCALIZATION OF STRETCH REFLEX

Abstract

[long dash]Localization of the stretch reflex within a single extensor muscle was investigated in decerebrate cats. A small muscle strip, 2-3 mm. in diam., was isolated from rectus femoris and its reflex response to a 3-mm. stretch was recorded by means of a RCA 5734 movable anode transducer. The concomitant tension of the remaining part of quadriceps was successively recorded. The reflex was highly localized in almost all cases since responses appeared only in the strip when it was stretched, while the rest of the muscle remained inactive. When the animal''s face was turned toward the limb under investigation, or when fast stretch rates or crossed extensor reflex was used to increase pool activity, the localization became gross. On the other hand, slow stretch rates or face away enhanced fine localization. The data were analyzed and developed to show that a preferential, very highly localized pathway exists which fires at relatively low levels of excitation of quadriceps motoneuron pool. At higher pool activity a secondary, diffuse localization pattern appears which produces stronger responses to stretch. Thus a double physiological activity is produced by a single anatomical arrangement.