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 GroupIIFree Nerve Endings: Projections From GroupsIIIandIVFree 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: