The monosynaptic Ia afferent pathway can largely explain the stretch duration effect of the long latency M2 response.
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.
Schuurmans
Jasper
J
Laboratory for Neuromuscular Control, Department of Biomechanical Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. j.schuurmans@tudelft.nl
de Vlugt
Erwin
E
Schouten
Alfred C
AC
Meskers
Carel G M
CG
de Groot
Jurriaan H
JH
van der Helm
Frans C T
FC
D000200:Action Potentials; D000328:Adult; D000704:Analysis of Variance; D001132:Arm; D003198:Computer Simulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D055815:Young Adult