Actions of afferent impulses from muscle receptors on cerebellar Purkynĕ cells. I. Responses to muscle vibration.

Abstract

Investigations were made in the decerebrate cat of the effect of muscle vibration on the activity of 342 Purkyně cells in the ipsilateral anterior lobe of the cerebellum. The effects were studied for three different muscle groups: in the hindlimb, the anterior tibial group (extensor digitorum longus, peroneus longus, brevis and tertius, and tibialis anterior) and gastrocnemius-soleus; and in the forelimb, the extensor digitorum lateralis and communis muscles. The responses of Purkyně cells were mediated by both the mossy fibre and climbing fibre inputs. The mossy fibre induced responses were generally inhibitory and had latencies only a few msec longer than responses evoked by stimulation of the nerve supplying the muscle. In contrast, the latencies of responses mediated by the climbing fibres were long and variable. Nine cells out of 342 Purkyně cells showed weak response to vibration of less than 60 μ amplitude, as compared to approximately 40% of those which responded to vibration of above 60 μ up to 200 μ amplitude, indicating the preponderant action of Group II afferents on the Purkyně cells in contrast to far less influence from Group Ia afferents. There was no obvious difference in threshold of vibration amplitude regarding the response mediated by the climbing or mossy fibres. Purkyně cell responses mediated by both mossy and climbing fibre inputs displayed temporal summation in response to muscle vibration, although no tonic effects were observed in response to maintained periods (1–5 sec) of vibration. Purkyně cell responses evoked by the mossy fibre input were unable to follow the individual cycles of vibration at frequencies above approximately 50 cps. Those evoked by the climbing fibres could follow at frequencies of less than 10 cps.