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Modulation of postural reflexes by voluntary movement
  1. Gerald L. Gottlieb,
  2. Gyan C. Agarwal
  1. Department of Biomedical Engineering, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60680, U.S.A.
  2. College of Engineering, University of Illinois at Chicago Circle, Chicago, Illinois 60680, U.S.A.

    Abstract

    We have observed that there is a brief, 400 msec period of widespread facilitation of both the Hoffmann and the tendon-jerk reflexes associated with the initiation of a variety of local, voluntary, isometric efforts. It is suggested that the site of this facilitation lies within the spinal cord. We have also observed that this period is followed, for the Hoffmann reflex, by a period of spinal inhibition. By contrast, the tendon-jerk is facilitated, at a reduced level, for at least another 500 msec by mechanisms probably working at the muscle spindle. These results are discussed in comparison with experiments involving activation of the reflex agonist and antagonist muscles. It is proposed that voluntary control of the locomotor system is organized through separate mechanisms for muscle recruitment and for regulation of the sensitivity of the myotatic reflex loop.

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    2. Modulation at an inactive joint

    Footnotes

    • 1 This work was supported in part by NSF grant GK-17581 and a PSL research grant.

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