Can fusimotor activity potentiate the responses of muscle spindles to a tendon tap?

D. L. Morgan, A. Prochazka, U. Proske

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Experiments on the cat soleus muscle have determined the effect of selective activation of the fusimotor system on the responses of muscle receptors to a simulated tendon tap. Primary endings of spindles responded in the passive muscle with an average 4.3 impulses at a mean instantaneous rate of 502 impulses/s. Static fusimotor stimulation at 100 pulses/s increased the number of impulses during the tap to 4.8 but dropped the mean instantaneous rate to 400 impulses/s. Dynamic fusimotor stimulation increased the number of impulses to 6.3 and the instantaneous rate to 557 impulses/s. Combined stimulation of the two axons gave intermediate values. We consider these effects as rather feeble. The tendon jerk in man shows a large increase in reflex amplitude following a reinforcement manoeuvre (Jendrassik manoeuvre). Based on our animal experiments we conclude that such increases cannot be accounted for simply in terms of selective engagement of the fusimotor system.

Original languageEnglish
Pages (from-to)209-215
Number of pages7
JournalNeuroscience Letters
Issue number1-3
Publication statusPublished - 7 Sept 1984


  • afferents
  • fusimotor reflex
  • motoneuron
  • muscle spindle
  • tendon jerk

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