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Motor Units and Their Activity during Movement

  • H. Peter Clamann

Abstract

The motor unit is the smallest functional subdivision of the neuromuscular system and, therefore, the smallest part of that system which can be controlled with any degree of independence. A motor unit is defined as a motoneuron, its axon, and all the muscle fibers which that axon innervates (Burke and Edgerton, 1975), although the original definition included only the axon and adjunct muscle fibers (Creed, Denny-Brown, Eccles, Liddell, and Sherrington, 1932; Liddell and Sherrington, 1925). Accepting the terminology of Burke (e.g., Burke, 1967), we will refer to the muscle fibers supplied by a single motoneuron as a muscle unit. A group of motor units, acting together, produces muscle force. The vast variety of movements of which we are capable—from tiny, precisely controlled motor acts to powerful, ballistic flailing of limbs—are all produced by varying numbers of motor units cooperating in different ways. This versatile repertoire of movements is brought about by two mechanisms: varying the number of motor units that are active or varying the discharge rate, and hence the force output, of individual motor units.

Keywords

Motor Unit Rate Code Medial Gastrocnemius Force Output Extraocular Muscle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Plenum Press, New York 1981

Authors and Affiliations

  • H. Peter Clamann
    • 1
  1. 1.Department of PhysiologyMedical College of VirginiaRichmondUSA

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