Some Effects of Receptor Muscle Contraction on the Responses of Slowly Adapting Abdominal Stretch Receptors of the Crayfish

Abstract

1. Stimulation of the motor fibres innervating the slowly adapting abdominal stretch receptors of the crayfish was carried out under the following circumstances: 2. With the receptors at a constant length the frequency of stimulation was varied. A maximal response from the receptors, which averaged about 50 impulses/sec, was obtained with stimulation rates of 50-80/sec. But low rates of stimulation (e.g. 10/sec.) had a powerful excitatory action, often 70% of maximal. 3. With the receptors stretched different amounts the motor fibres were stimulated at a constant rate. The increase in the receptor discharge caused by the contraction was the same over the range of lengths studied. 4. The receptors were stretched at a series of constant velocities (0.05-10 mm./sec.) to the same final length with and without motor-nerve stimulation. The contraction increased the frequency rise during the dynamic phase of stretch and increased the amount by which the frequency decayed at the end of the ramp. 5. The phasic response of the de-efferented receptor has previously been described by the following transfer function Fs=aΓ (1-k)sk, where a and k are constants. To a first approximation the effect of receptor contraction on this phasic response was to increase the value of the constant a, but to leave k unaffected.