Neural Control of Muscle Length and Tension

Abstract

The sections in this article are: Control Theory Concepts Systems and Models Control Systems Feedback, Feedforward, and Adaptive Systems Principle of Negative Feedback Regulated Variables and Properties Control Configurations Summary Hypotheses of Motor Servo Function Salient Features of the Available Sensors Follow‐up Servo Hypothesis Spindle Receptors as Model‐Reference Error Detectors Conditional Feedback and Servo Assistance β‐System and the Possibility for Zero Sensitivity Stiffness Regulation Summary Model Adaptive Models Summary Muscle Mechanical Stiffness Stiffness Definitions Length Dependence Recruitment of Motor Units Rate Modulation of Motor Units Instantaneous Stiffness and Short‐Range Elasticity Instantaneous Stiffness Beyond the Short‐Range Region Ramp Responses: Transient Properties and Nonlinearity Natural Combinations of Recruitment and Rate Modulation Summary Central Pathways Primary Ending Projections Tendon Organ Projections Projections From Secondary Endings and Group II Free Nerve Endings Projections From Groups III and IV Free Nerve Endings Clasp‐Knife Reflex Long‐Loop Reflexes Summary Simplified Animal Models Decerebrate Preparation Spinal Preparation Summary Tonic Stretch Reflex in Functionally Isolated Muscles Basic Features of the Stretch Reflex Static Force‐Length Relations Normalized Stiffness Mechanically and Neurally Mediated Components Actions of Control Signals on the Motor Servo Dependence of Incremental Stiffness on Initial Force Loop Gain of Force Feedback Summary Static Regulatory Characteristics in Intact Subjects Skeletal Mechanics and Coordinate Systems Steady‐State Responses to Changes in Load Force Torque‐Angle Relations Equivalent Stiffness and the Concept of Composite Motor Servos Effect of Instructional Set Gain Variation vs. Gain Control Summary Dynamic Responses to Mechanical Disturbances Dynamic Features of Force Development Dependence of Transient Responses on Initial Force Amplitude Dependence and Linearity Asymmetry of Motor Servo Response Compensation for Yielding Predictive Compensation: Feedforward vs. Nonlinear Feedback Viewpoints Vibration and the Stretch Reflex Velocity Dependence and Damping Summary Implementation of Movement Commands α‐γ‐Relations Positional Stiffness Deduced From Spindle Relations β‐Innervation of Muscle Spindles Analytical Approaches to Actions of α‐, β‐, and γ‐Motoneurons Equilibrium Point Control Stiffness Regulation vs. Stiffness Control Perturbations During Movement Compliance, Load Compensation, and Biological Design Summary

Control of position and movement is simplified by combined muscle spindle and Golgi tendon organ feedback

“…Typically, muscle spindles are included in computational models of motor control as simple muscle length and contraction velocity sensors that are used for low-level feedback control of (joint) position and velocity (e.g., de Vlugt et al 2002;Feldman 2009;Gribble et al 1998;Houk and Rymer 2011;Inbar 1972;Kandel et al 2000;McIntyre and Bizzi 1993). In the simulations described in this study, we adopt a similar approach.…”

Delayed Visual Feedback Affects Both Manual Tracking and Grip Force Control When Transporting a Handheld Object

“…Predictive mechanisms are necessary because of the delays associated with visual and proprioceptive feedback pathways and the instability that those delays can induce in feedback controllers (Desmurget and Grafton 2000;Houk and Rymer 1981;. Predictive mechanisms have been demonstrated in motor behaviors as diverse as object manipulation, locomotion, gaze orientation, or manual tracking (Bastian 2006;Flanagan et al 2003;Miall and Jackson 2006;Vaziri et al 2006).…”

Physiological Basis of Limb-Impedance Modulation During Free and Constrained Movements

“…First, the agonistantagonist architecture of the muscular system allows for impedance control by the CNS (Hogan 1984;Houk and Rymer 1981;Humphrey and Reed 1983;Smith 1981). Because the stiffness of the muscle is dependent on its activation, the CNS can affect the mechanical impedance of the limb by adjusting alpha-motoneuron activation in opposing muscles.…”