Presynaptic Inhibition induced by Muscle Stretch

Abstract

THE existence of a powerful inhibitory mechanism acting at the level of the primary afferent fibre has been well demonstrated¹. The method by which this presynaptic inhibitory pathway acts is generally accepted to be through a prolonged depolarization of the central terminals of the primary afferent fibres with, as a consequence, depression of the amount of excitatory transmitter substance liberated by their synaptic terminals. This depolarization of the central terminals of a particular group of primary afferent fibres is effected in a rather specific manner by afferent impulses from some types of receptors and not from others. For example, the group I afferent impulses entering the spinal cord through the sensory fibres of the nerve to a flexor muscle (but not an extensor) will produce a prolonged depolarization of the central terminals of the primary afferent fibres from annulospiral endings of muscles of that limb, both flexors and extensors.