The monosynaptic Ia afferent pathway can largely explain the stretch duration effect of the long latency M2 response

Jasper Schuurmans, Erwin De Vlugt, Alfred C. Schouten, Carel G.M. Meskers, Jurriaan H. De Groot, Frans C.T. Van Der Helm

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Sudden stretch of active muscle typically results in two characteristic electromyographic responses: the short latency M1 and the long latency M2. The M1 response originates from the monosynaptic Ia afferent reflex pathway. The M2 response is less well understood and is likely a compound response to different afferent inputs mediated by spinal and transcortical pathways. In this study the possible contribution of the Ia afferent pathway to the M2 response was investigated. A mechanism was hypothesized in which the M1 response synchronizes the motoneurons, and therewith their refractory periods. Stretch perturbation experiments were performed on the wrist and results were compared with a computational model of a pool of motoneurons receiving tonic and Ia afferent input. The simulations showed the same stretch amplitude, velocity, and duration-dependent characteristics on the M2 as found experimentally. It was concluded that the stretch duration effect of the M2 likely originates from the proposed Ia afferent mediated mechanism.

Original languageEnglish
Pages (from-to)491-500
Number of pages10
JournalExperimental Brain Research
Issue number4
Publication statusPublished - 1 Mar 2009


  • Ia afferent
  • M2 response
  • Stretch reflex

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