Authors: Leonardo Abdala Elias Vitor Martins Chaud André Fabio Kohn
Publish Date: 2012/05/06
Volume: 33, Issue: 3, Pages: 515-531
Abstract
Motoneuron MN dendrites may be changed from a passive to an active state by increasing the levels of spinal cord neuromodulators which activate persistent inward currents PICs These exert a powerful influence on MN behavior and modify the motor control both in normal and pathological conditions Motoneuronal PICs are believed to induce nonlinear phenomena such as the genesis of extra torque and torque hysteresis in response to percutaneous electrical stimulation or tendon vibration in humans An existing largescale neuromuscular simulator was expanded to include MN models that have a capability to change their dynamic behaviors depending on the neuromodulation level The simulation results indicated that the variability standard deviation of a maintained force depended on the level of neuromodulatory activity A force with lower variability was obtained when the motoneuronal network was under a strong influence of PICs suggesting a functional role in postural and precision tasks In an additional set of simulations when PICs were active in the dendrites of the MN models the results successfully reproduced experimental results reported from humans Extra torque was evoked by the selfsustained discharge of spinal MNs whereas differences in recruitment and derecruitment levels of the MNs were the main reason behind torque and electromyogram EMG hysteresis Finally simulations were also used to study the influence of inhibitory inputs on a MN pool that was under the effect of PICs The results showed that inhibition was of great importance in the production of a phasic force requiring a reduced cocontraction of agonist and antagonist muscles These results show the richness of functionally relevant behaviors that can arise from a MN pool under the action of PICs
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