Summary
In approximately 3/4 of precollicular decerebrate (unanesthetized) cats, tetanic electrical stimulation of the sural nerve, or pinching the ankle skin innervated by the sural nerve, produced predominant excitation (overall increased force output and EMG activity) in the mixed medical gastrocnemius (MG) muscle and simultaneous inhibition in its slow twitch Synergist, soleus (Sol). The present experiments were designed to test whether, as this and other evidence suggests, certain sets of cutaneous afferents can produce activation of particular groups of motor units and simultaneous inhibition of other groups within the same motor unit pool (i.e., units belonging to a single muscle).
We recorded, in decerebrate cats, the activity of restricted sets of MG motor units using either fine bipolar EMG wire electrodes or bipolar hook electrodes on small natural filaments of the MG muscle nerve. In preparations exhibiting the differential effect of sural input noted above, we usually found that some low threshold MG motor units (i.e., those responding to stretch or vibration of the MG muscle) exhibited slowing of discharge or complete inhibition at the same time that higher threshold MG units, not responsive to stretch or vibration, were powerfully recruited by either electrical or natural stimulation of sural nerve afferents. The net balance of synaptic effects within the MG motoneuron population may thus be excitatory in some cells and simultaneously inhibitory in others. This finding, together with earlier evidence, suggests the existence of at least two patterns of organization of synaptic input to the MG motoneuron pool.
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Kanda, K., Burke, R.E. & Walmsley, B. Differential control of fast and slow twitch motor units in the decerebrate cat. Exp Brain Res 29, 57–74 (1977). https://doi.org/10.1007/BF00236875
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DOI: https://doi.org/10.1007/BF00236875