Recruitment and Discharge Patterns of Single Motor Units During Speech Production Recruitment and discharge patterns of single motor units (MUs) in the anterior belly of digastric were studied during speech in three subjects, using electrodes facilitating selective recording at high force levels. Fixed recruitment order was observed in over 99% of all comparisons. Later recruited units invariably possessed muscle action potentials ... Research Article
Research Article  |   December 01, 1977
Recruitment and Discharge Patterns of Single Motor Units During Speech Production
 
Author Affiliations & Notes
  • Harvey M. Sussman
    University of Texas, Austin
  • Peter F. MacNeilage
    University of Texas, Austin
  • Randall K. Powers
    University of Texas, Austin
Article Information
Research Articles
Research Article   |   December 01, 1977
Recruitment and Discharge Patterns of Single Motor Units During Speech Production
Journal of Speech, Language, and Hearing Research, December 1977, Vol. 20, 613-630. doi:10.1044/jshr.2004.613
History: Received January 12, 1977 , Accepted April 5, 1977
 
Journal of Speech, Language, and Hearing Research, December 1977, Vol. 20, 613-630. doi:10.1044/jshr.2004.613
History: Received January 12, 1977; Accepted April 5, 1977

Recruitment and discharge patterns of single motor units (MUs) in the anterior belly of digastric were studied during speech in three subjects, using electrodes facilitating selective recording at high force levels. Fixed recruitment order was observed in over 99% of all comparisons. Later recruited units invariably possessed muscle action potentials of higher amplitude, suggesting that units were activated in accordance with the “size principle.” Additional evidence for this was that later recruited units, of a set of three studied during speech, motor unit training, and isometric force ramps, showed greater sensitivity to input, and greater dynamic range than earlier recruited units. Units in this set were much more sensitive to rapid changes in input associated with speech gestures than to static activation even at high force levels. Several significant relations between discharge characteristics and aspects of movement dynamics were observed, including relations between (1) recruitment interval (MU1 to MU3) and latency of mandibular lowering, (2) onset of initial discharge of MU1 and relative mechanical advantage of the mandible, (3) number of MUs active and velocity and displacement of the mandible, and (4) discharge rate of MU3 and velocity and displacement of the mandible.

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