Simulations of the alpha motoneuron pool electromyogram reflex at different preactivation levels in man

Abstract

The alpha motoneuron pool and the surface electromyogram (EMG) of the human soleus muscle are modelled, respectively, by an alpha motoneuron pool model generating the firing patterns in the motor units of the muscle and by a muscle model using these discharge patterns to simulate the surface EMG. In the alpha motoneuron pool model, we use a population of motoneurons in which cellular properties like cell size and membrane conductance are distributed according to experimentally observed data. By calculating the contribution from each motor unit, the muscle model predicts the EMG. Wave forms of the motor unit action potentials in the surface EMG are obtained from experimental data. Using the model, we are able to give a quantitative prediction of the motoneuron pool activity and the reflex EMG output at different preactivation levels. The simulated data are consistent with experimentally obtained results in healthy humans. During static isometric muscle preactivations, the simulations show that the reflex strength is highly dependent on the intrinsic threshold properties of the alpha motoneuron pool.

Temporal Evolution of “Automatic Gain-Scaling”

“…This modulation likely reflects the intrinsic organization of the motoneuron pool whereby motor units are recruited in strict order of their force-generating capability and resilience to fatigue (Cope and Clark 1991; Henneman 1957), a phenomenon termed the size-recruitment principle. Indeed previous work has convincingly described (Marsden et al 1976;Matthews 1986) and formalized (Capaday and Stein 1987;Houk et al 1970;Kernell and Hultborn 1990;Slot and Sinkjaer 1994) how the size-recruitment principle specifically leads to gain-scaling, and empirical studies have demonstrated that the size-recruitment principle likely applies to motor-unit recruitment at all latencies (short, long and voluntary) following a mechanical perturbation (Calancie and Bawa 1985a,b).…”

“…This modulation is generally attributed to the intrinsic organization of the motoneuron pool (Capaday and Stein 1987;Houk et al 1970;Kernell and Hultborn 1990;Marsden et al 1976;Matthews 1986;Slot and Sinkjaer 1994) where motor units are recruited in order of their force-generating capability and resilience to fatigue (Cope and Clark 1991; Henneman 1957), a phenomenon termed the size-recruitment principle. Although gainscaling may be a useful short-term strategy (Bedingham and Tatton 1984;Marsden et al 1976;Matthews 1986), ultimately the steady-state response to an additional load must be independent of preperturbation muscle activity (i.e., not show gain-scaling) given the largely linear relationship between load and muscle activity for low to moderate loads (Hof 1984;Lawrence and Deluca 1983;Milner-Brown and Stein 1975).…”

Excitatory drive to the alpha‐motoneuron pool during a fatiguing submaximal contraction in man.

“…On the other hand, the range of excitatory drive over which the H reflex can increase might be limited. Indications come from modelling studies that an activation of all MUs might occur at submaximal contraction levels due to a compressed range of excitability necessary to recruit these MUs (Fuglevand, Winter & Patla, 1993;Slot & Sinkjaer, 1994). In order to assess the range of excitatory drive over which the H reflex can increase, it will be necessary to study H reflexes at several levels of underlying contraction.…”

Sistema de simulação de circuitos neuronais da medula espinhal desenvolvido em arquitetura web.

“…Dentro desta categoria, duas grandes vertentes podem ser notadas: trabalhos em que se supôs que a ação de um conjunto de motoneurônios ou interneurônios podia ser representada pelo modelo de um único motoneurônio ou interneurônio (IVASHKO et al, 2003;JILGE et al, 2004;PIOTRKIEWICZ;MIERZEJEWSKA, 2004); trabalhos em que as diferenças entre características biofísicas de diferentes motoneurônios e as fibras musculares inervadas foram modeladas (AKAZAWA; KATO, 1990;SLOT;SINKJAER, 1994;HECKMAN;RYMER, 1998;NUSSBAUMER et al, 2002;WINDHORST, 2003a;CISI;KOHN, 2004 Segundo et al (1968), e as células de Renshaw, por simplificação matemática, são representadas por um único elemento.…”