Functional properties of tendon receptors in the frog.

Abstract

1. Afferent discharges from the tendon receptors in the pelvic and tibial ends (with some of knee joint capsules) of the frog's sartorius muscle were recorded from the 8th and 9th dorsal roots respectively.2. In 45 out of 54 receptors tested, small spike discharges with conduction velocities of from 5 to 35 m/sec (25-28°C) occurred with thresholds from 0.5 to 2g tensions during isometric contractions of the muscle, and the number and frequency of the discharges increased with increases of the tension.The remaining 9 receptors were characterized by large spikes with conduction velocities from 35 to 45m/sec and by rapid adaptation.3. During shortening of the muscle against loads, all the receptors responded with only one discharge at the peak of tension development d ue to acceleration of the weight by the shortening muscle.4. During muscle stretch at constant velocities, 38 receptors (31 smallspikeand 7 large-spike) discharged phasically during the dynamic phas e of stretch by 4mm from initial lengths of more than+6mm.The other 14 receptors (11 small-spike and 3 large-spike) responded to stretch by 4mm from initial lengths of more than+4mm.The remaining two receptors were characterized by sustained discharges during muscle stretch of 4mm from +2mm initial length.The static index of the sustained discharge was independent of the velocity of the stretch and the static sensitivity was 3.73 impulses/sec/mm in the mean.Various dynamic indexes were observed with different velocities of muscle stretch or with different initial muscle lencrths.5. It was suggested that these functional properties of the tendon receptors may be resemble to those of the leaf-like muscle receptors, and that the activities may be attributed to an inverse myotatic reflex by which excessive stresses to the muscle are eliminated.