Self-Regulation of the Muscle Contraction by Facilitation and Inhibition from its Proprioceptors

Abstract

IN order to approach the question raised by the title of this communication, we need a method of testing the excitability of the motoneurones of one muscle, and of that muscle alone, while the muscle itself is contracting or passively stretched. To this end we make use of the properties of the monosynaptic arc analysed by Lloyd^1,2. (i) A weak electrical test shock (see left half of diagram), set up through electrodes on the nerve of the ankle extensors (cat under ‘Dial'), delivers a fast volley through the monosynaptic path in the spinal cord, faster than any other impulses, and this volley can be picked up at the point marked ‘recording’ on the central stump of the halved ventral root S₁. The other ventral roots from L₅ backwards have been severed and the leg denervated except for the nerve to the ankle extensors, (ii) The monosynaptic volley traverses fibres which, on the afferent side, originate in, and, on the efferent side, return to, the muscle concerned, so that the test shock actually tests the excitability of its motoneurones alone.