Ent of key afferents. Additionally, continuous curves show the instantaneous firing price (estimated by a Gaussian kernel convolved using the spike trains) for three Ia afferents (four, 16, 28). (D-F) Raster plots for group II excitatory interneurons (INs), Ib inhibitory INs, and Ia inhibitory INs. Continuous curves in panels D and E represent the instantaneous firing rate for two type-specified INs (2 and 94 for group II INs; 24 and 94 for Ib INs). (G-I) Raster plots for sort II afferents from MG muscle spindle, Ib afferents from MG muscle spindle, and Ia afferents from TA muscle spindle. Continuous curves in panels G and H represent the instantaneous firing rate of two type-specified afferent fibres (9 and 28 for type-II afferents; 22 and 39 for Ib afferents). doi:ten.1371/journal.pcbi.1003944.gPLOS Computational Biology | www.ploscompbiol.orgLarge-Scale Neuromusculoskeletal Model of Human Upright StandingFigure 5. Common behaviour of Soleus (SO) motor units (MUs) and Ia afferents. (A) Raster plots (black dots) and SO electromyogram PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/20176928 (EMG) envelope (red curve). Note that the SO muscle has an about steady activation throughout postural sway (not an excessive amount of recruitment and de-recruitment). (B) Raster plots from SO muscle spindle Ia afferents and instantaneous firing rate for two chosen afferents (continuous curves for afferents 15 and 51). Note the smaller modulation in Ia afferent recruitment and firing rate. doi:ten.1371/journal.pcbi.1003944.gimately the COM/COP displacement (note the firing rate modulation for 3 distinctive Ia afferents, as indicated by the thin lines). Since there was small variation inside the MG muscle torque (RMS value two.50 of the maximum MG muscle torque) as well as the mean MG muscle fibre length was maintained at an about steady value (i.e., there was small change in the static component of the muscle fibre length – see under), the activities of Ib and form II afferents have been minimally modulated (see panels G and H in Figure four). The proprioceptive pathways accountable for the reciprocal inhibition had been also very modulated for the duration of postural sway (see panels F and I in Figure 4). Inhibitory Ia INs discharged phasically when the inverted pendulum swayed backward and this contributed to a reduce within the ankle joint torque generated by the plantar flexor muscle tissues. Conversely, Ia afferents in the SO muscle spindles have been poorly modulated inside the posture control activity (see Figure 5B). The intermittent recruitment of MG MUs was evaluated on the basis of two phase plots that relate angular velocity and muscle torque with ankle angle data obtained in the postural handle model (Figure 6). Figure 6A shows that a lot of the MG MUs (60 ) have been recruited when the inverted pendulum was leaning forward from its equilibrium position irrespective of its velocity (first and fourth quadrants of the angle-velocity phase plots). Nonetheless, a big SR9011 (hydrochloride) chemical information variety of MUs (28 ) had been recruited when the inverted pendulum was at a backward position but having a constructive velocity (second quadrant), i.e., the pendulum was starting to return to a forward position. Similarly, the majority of the MG MUs (50 ) have been recruited when the pendulum was leaning forward and creating a larger plantar flexion torque (fourth quadrant within the Figure 6B), i.e., the pendulum was at a forward position and decelerating. Just about 35 from the MUs have been recruited when the pendulum was at a backward position and using a decrease (morePLOS Computational Biology | www.ploscompbiol.orgFigure.
