Neural Regulation of Limb Mechanics: Insights from the Organization of Proprioceptive Circuits

Abstract

Sensory feedback arising from muscle spindle receptors and Golgi tendon organs are known to influence limb mechanics during postural and locomotor tasks. The purpose of this chapter is to synthesize data concerning the organization and actions of these proprioceptive pathways, and then to propose how current models can be used to promote understanding of their functional role in regulating whole limb stiffness. Following a historical introduction, the role of length feedback in transforming the mechanical properties of muscles into more spring-like actuators is reviewed. Next, we describe the organization of intermuscular length and force feedback circuits in the context of the mechanical interrelationships of the muscles involved. Finally, we provide a conceptual framework for understanding the role of proprioceptive feedback in the regulation of limb mechanics across a continuum of behaviors, and show how a developing computational model can be used to understand how these pathways are integrated to regulate limb stiffness. We conclude from a qualitative appraisal of the data that intermuscular length feedback reinforces the mechanical relationships between antagonists and between synergistic muscles that cross the same or different joints. Furthermore, inhibitory force feedback is organized to manage the distribution of stiffness across joints as well as intersegmental dynamics due to the inertial properties of the limb segments.