External Intercostal and Phrenic a Motor Responses to Changes in Respiratory Load

Abstract

Abstract The hypothesis that the fusimotor—muscle spindle system in its control of physiologically induced movements automatically adjusts the a motor activity to achieve“wanted” length changes in spite of some variations in load that may occur has been examined for the respiratory movements of external intercostal muscles and the diaphragm after bilateral vagotomy in cats under light pentobarbital anaesthesia. The afferent activity from intercostal muscle spindles increased in response to an increase in respiratory load produced by tracheal occlusion. Efferent intercostal a motor activity was reflexely enhanced in response to such an increase in load, an effect which was abolished after section of the dorsal roots of the same and adjacent segments. The efferent phrenic a motor activity and the electrical activity of the diaphragm did not show this response to tracheal occlusion indicating a principal difference in proprioceptive control of the external intercostal muscle and the diaphragm.