Coupling between human muscle spindle endings and motor units assessed using spike-triggered averaging.
The electromyographic activity (EMG) generated by voluntary contraction of a muscle was averaged using the potentials from 18 identified muscle spindle afferents as a trigger. In post-spike averages of 1000-10,000 sweeps, no evidence of reflex excitation of the homonymous motoneurone pool was detected. In pre-spike averages there was no evidence of a motor-unit EMG potential that was closely correlated to the trigger spike. A single spindle afferent has only a weak reflex effect on an active motoneurone pool and must be part of a synchronized volley to affect motoneurone discharge significantly. No evidence was found for spindle activation via beta-motoneurones in weak voluntary contractions.
D000818:Animals; D002415:Cats; D003655:Decerebrate State / Q000503:physiopathology; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction; D009470:Muscle Spindles / Q000502:physiology*; D009132:Muscles / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology; D013569:Synapses / Q000502:physiology