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On the function of muscle and reflex partitioning

Published online by Cambridge University Press:  04 February 2010

Uwe Windhorst
Affiliation:
Abteilung Neuro- und Sinnesphysioiogie, Zentrum Physiologie und Pathophysiologie der Universität Göttingen, Federal Republic of Germany
Thomas M. Hamm
Affiliation:
Barrow Neurological Institute, Division of Neurobiology, St. Joseph's Hospital and Medical Center, 350 West Thomas Road, Phoenix, AZ 85013* Electronic mail: araxc@asuacad.bitnet
Douglas G. Stuart
Affiliation:
Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ 85724

Abstract

Studies have shown that in the mammalian neuromuscular system stretch reflexes are localized within individual muscles. Neuromuscular compartmentalization, the partitioning of sensory output from muscles, and the partitioning of segmental pathways to motor nuclei have also been demonstrated. This evidence indicates that individual motor nuclei and the muscles they innervate are not homogeneous functional units. An analysis of the functional significance of reflex localization and partitioning suggests that segmental control mechanisms are based on subdivisions of motor nuclei–muscle complexes. A partitioned organization of segmental control mechanisms could utilize (1) the potential functional diversity of muscle fiber types, (2) the variety of mechanical actions of individual muscles arising from their distributed origins and insertions, and (3) diverse architectural features such as intramuscular variations in pinnation and complex in-series and in-parallel arrangements of muscle fibers. The differentiated activity observed in some muscles during natural movements also calls for localized segmental control mechanisms. Partitioning may also play a role in mechanical interactions between contracting motor units and in increasing the stability of neuromuscular systems. The functional advantages of reflex localization and partitioning suggest they are probably common features of segmental systems, whose organization reflects the structure and function of their associated neuromuscular systems.

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Target Article
Copyright
Copyright © Cambridge University Press 1989

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