41: Posture

Introduction

• Postural Equilibrium and Orientation Are Distinct Sensorimotor Processes

• Postural Equilibrium Requires Control of the Body's Center of Mass

  • Balance During Stance Requires Muscle Activation

  • Automatic Postural Responses Counteract Unexpected Disturbances

  • Automatic Postural Responses Adapt to Changes in the Requirements for Support

  • Anticipatory Postural Adjustments Compensate for Voluntary Movements

• Postural Orientation Is Important for Optimizing Execution of Tasks, Interpreting Sensations, and Anticipating Disturbances to Balance

• Sensory Information from Several Modalities Must Be Integrated to Maintain Equilibrium and Orientation

  • Somatosensory Afferents Are Important for Timing and Direction of Automatic Postural Responses

  • Vestibular Information Is Important for Balance on Unstable Surfaces and During Head Movements

  • Visual Information Provides Advance Knowledge of Potentially Destabilizing Situations and Assists in Orienting to the Environment

  • Information from a Single Sensory Modality Can Be Ambiguous

  • The Postural Control System Uses a Body Schema that Incorporates Internal Models for Balance

  • The Influence of Each Sensory Modality on Balance and Orientation Changes According to Task Requirements

• Control of Posture Is Distributed in the Nervous System

  • Spinal Cord Circuits Are Sufficient for Maintaining Antigravity Support but Not Balance

  • The Brain Stem and Cerebellum Integrate Sensory Signals for Posture

  • The Spinocerebellum and Basal Ganglia Are Important in Adaptation of Posture

  • Cerebral Cortex Centers Contribute to Postural Control

• An Overall View

The control of posture is crucial for most tasks of daily living. The two components of posture, orientation and balance, require continual adjustment and involve several sensory systems.

To appreciate the complexity of maintaining balance and orientation, imagine that you are waiting tables on a tour boat. You have a tray full of drinks to be delivered to a table on the other side of the rolling deck. Even as your mind is occupied with remembering customer orders, unconscious processes allow you to move about in a smooth and coordinated manner.

The apparently simple task of delivering drinks is supported by a truly complex sensorimotor process for controlling postural orientation and balance. As you cross the deck your brain rapidly processes sensory information and adjusts motor output to maintain your balance, the upright orientation of your head and trunk, and stable arms supporting the tray of full glasses. Before you reach out to place a glass on the table, your nervous system makes anticipatory postural adjustments to maintain your balance. Sudden unexpected motions of the boat evoke automatic postural responses that prevent falls. Somatosensory, vestibular, and visual information is integrated to provide a coherent picture of the position and velocity of the body in space and to generate and update motor commands that maintain balance and orientation.

Postural Equilibrium and Orientation Are Distinct Sensorimotor Processes

Postural equilibrium, or balance, involves active resistance to external forces acting on the body. The dominant external force affecting equilibrium on earth is gravity. Postural orientation is the positioning of body segments with respect to each other and to the ...