Reflex regulation of antagonist muscles for control of joint equilibrium position

Abstract

A systems model of spinal neuro-musculo-skeletal system (alpha - gamma model) is developed to investigate the plausible roles of spinal proprioceptive feedback in movement control. The model is composed of a joint, a pair of antagonist muscles, length and velocity feedback from muscle spindle, as well as spinal stretch reflex, reciprocal inhibition and recurrent inhibition of Renshaw cells. A descending command modulates the background activation of alpha motoneuron pools in combination with these reflex activities. A static gamma command controls the fusimotor contraction of the spindle. Simulation results reveal that the equilibrium joint angle is linearly correlated to the level of static gamma fusimotor activity of the spindle for a wide range of external loading conditions and reflex gains, suggesting that these spinal reflexes may contribute to regulate the equilibrium position of the joint. Sensitivity analysis further shows that reflex gains and other central commands alter the quasi-linear relation in regular fashions. The reciprocal inhibition gain changes the slope of the linear theta(eq) - gamma curve; and the descending alpha excitation, the stretch reflex gain, and the external load all shift the theta(eq) - gamma curve in parallel. These results imply that reflex gains and descending alpha commands may be coordinated to maintain a unique theta(eq) - gamma curve while providing the flexibility to counteract external loads, to execute a movement, or to regulate additional muscle variables. Dynamic simulation suggests that control of a class of movements can be achieved with a triphasic, alpha pulse and a continuous gamma signal. The model study supports the notion of a dual strategy for controlling trajectories via a feedforward alpha command and for regulating the final equilibrium positions via a feedback gamma command.

Spinal-Like Regulator Facilitates Control of a Two-Degree-of-Freedom Wrist

“…2, 3). This is a key distinction compared to previous models of spinal circuitry (Feldman, 1966;Bullock and Grossberg, 1992;Bullock et al, 1993;Bashor, 1998;van Heijst et al, 1998;Ostry and Feldman, 2003;Lan et al, 2005;Maier et al, 2005), but it is more consistent with the actual neuroanatomy. This also appears to be the first model of spinal cord circuitry to deal with the shifting patterns of synergistic and antagonistic muscle activity that necessarily accompany multimuscle, multi-degree-offreedom systems.…”

“…Over the past 20 years, there have been several attempts to model the lower sensorimotor system for voluntary movement, but they were usually restricted to a hinge joint operated by an antagonist muscle pair and they usually incorporated only a small subset of the known spinal circuitry (Feldman, 1966;Bullock and Grossberg, 1992;Bullock et al, 1993;Bashor, 1998;Feldman et al, 1998;van Heijst et al, 1998;Ostry and Feldman, 2003;Lan et al, 2005;Maier et al, 2005). Loeb et al (1990) introduced linear quadratic regulator design to find optimal solutions for reflex gains in a multisegment limb model (He et al, 1991), but there was no way to reconcile these gains with the actual interneuronal elements of the spinal cord.…”

Building a realistic neuronal model that simulates multi‐joint arm and hand movements in 3D space

“…In a further step to build a realistic model for movement simulation, a single joint model with one pair of antagonist muscles was constructed with a linear spindle sensor and spinal reflex circuits (stretch reflex, reciprocal inhibition, and recurrent inhibition) (Lan et al, 2005a). This system's model was able to demonstrate separate control of final equilibrium (or target) position and movement trajectory via a ␥ static, descending command and a triphasic, ␣ excitation command, consistent with the pulse-step hypothesis (Ghez, 1979) and the dual control strategy for posture and movement inferred from deafferented human reaching movements (Gordon et al, 1995).…”

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

“…Simuladores que utilizam relações entrada-saída de grandes blocos, como a relação entre corrente de entrada estática e freqüência de disparo em motoneurônios ou força desenvolvida por uma unidade motora; a relação entre grau de alongamento muscular estático e força desenvolvida; relação entre freqüência de disparo de uma célula de Renshaw equivalente em função da média ponderada das taxas de disparo dos motoneurônios; equações diferenciais de primeira ordem para representar a influência de ativação descendente sobre a atividade do conjunto de motoneurônios PATLA, 1993;GRAHAM;REDMAN, 1993;ZHOU;RYMER, 2004a;LAN et al, 2005).…”