Nature of the Persisting Canges in Afferent Discharge from Muscle following its Contraction

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This chapter discusses the nature of the persisting canges in afferent discharge from muscle following its contraction. In an experiment presented in the chapter, the postcontraction increase in sensory discharge is observed to study the effects of tenotomy. Several conclusions are drawn from these observations—a persisting increase in discharge at a maintained muscle length and in response to stretch appears after a muscle has undergone contraction, under the condition that the efferent background is otherwise quiet; fusimotor activation alone—that is, contraction of intrafusal fibers, can produce this effect, though extrafusal contraction also seems to contribute; the enhanced discharge, as it is recorded, arises to a major extent in Ia afferent fibers; and the cause of the effect is probably of a mechanical nature. It is believed that the cause of the postcontraction effect is mechanical, rather than due to the sensory ending being affected by a contraction-induced change in the metabolic milieu. Momentary stretch of the muscle results in an immediate disappearance of the postcontraction effect; it is unlikely that this action would rapidly dispel an excess accumulation of metabolite that is capable of such long-lasting effect. The duration of stimulus needed for the response is a few tenths of a second; excitatory levels of K + would probably not build up in this time.