[From posture to initiation of movement].
Purposeful motor acts are subjected to two contradictory constraints. One is to move one or several body segments toward a goal, the other is to stabilize other segments in order to maintain posture and equilibrium. One of the major tasks of the central nervous system is to coordinate posture and movement. Human posture is built up from the superposition of several "modules' from the ground to the head. Each module, tied to the next one by muscles, has its proper central and reflex regulation which permits to maintain its position in relation to the underlying one. In addition, a global regulation of posture is apparent (postural tone). Equilibrium is maintained under static conditions when the center of gravity projects onto the ground within the supporting surface (feet). Sensory error detecting signals (visual, labyrinthine, proprioceptive) are correcting, through a feedback loop, the reference regulated value according to a "postural' body schema based on "metric' and "dynamic' inputs. Corrections are continuous (and slow) or discontinuous and phasic through a repertoire of synergies allowing fast corrections. During movement performance, posture and equilibrium are stabilized by "anticipatory postural adjustments'. Some are aimed at maintaining the equilibrium notwithstanding the displacement of body segments due to the movement; others stabilize one or several segments such as the head, the trunk or the arm, which serve as reference value for the calculation of the movement trajectory and for the accurate performance of the movement. The anticipatory adjustments are learned during childhood or during training for specific tasks. The adaptative networks built up for a given movement are then controlled by the movement related command signals. The central organization of these anticipatory postural adjustments relies on central brain structures involved in movement execution and movement organization. Deficit is seen in spastic patients, to some extent in cerebellar patients. Basal ganglia and premotor areas, including the supplementary motor area, are of importance for coordination between posture and movement. This suggests that one of their function might be to stabilize posture during movement performance in order to ensure precise reaching of the goal. A specific pathology of the anticipatory postural adjustments should thus be considered.
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Laboratoire de Neurosciences Fonctionnelles, CNRS Marseille.
D000818:Animals; D006801:Humans; D009043:Motor Activity / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology; D009068:Movement / Q000502:physiology*; D009069:Movement Disorders / Q000209:etiology / Q000503:physiopathology; D009132:Muscles / Q000502:physiology; D009424:Nervous System Physiological Phenomena; D004856:Postural Balance / Q000502:physiology; D011187:Posture / Q000502:physiology*
Posture et préparation du mouvement.