Control of soleus motoneuron excitability during muscle stretch in man.

The relative contributions of intramuscular and extramuscular receptors to changes in the reflex excitability of soleus motoneurons, following muscle stretch, have been studied in man. It was found that reflex excitability was decreased by muscle stretch. The extent of the decrease was related to the amount of stretch, irrespective of whether the latter was produced by dorsiflexion of the ankle or by depression of the Achilles tendon with the ankle joint fixed. The results were unaffected by anaesthesia of the skin. It would appear that neither joint receptors nor cutaneous mechanoreceptors contribute significantly to the decrease in reflex excitability during ankle dorsiflexion and that the intramuscular receptors are mainly responsible for the effects observed.