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Summation of extraocular motor unit tensions in the lateral rectus muscle of the cat
Author(s) -
Goldberg Stephen J.,
Wilson Kristi E.,
Shall Mary S.
Publication year - 1997
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/(sici)1097-4598(199710)20:10<1229::aid-mus4>3.0.co;2-e
Subject(s) - isometric exercise , motor unit , anatomy , extraocular muscles , superior rectus muscle , stimulation , medial rectus muscle , muscle contraction , chemistry , medicine
Contractile measures on 67 single muscle units in the cat lateral rectus muscle were made in response to motoneuron stimulation. Simultaneous activation of four to five additional units, using muscle nerve stimulation, allowed an examination of unit force summation. Linear force addition was found in 73% of the units, while 25% added only about half of their twitch force to the twitch force of the nerve‐activated units. “Nonadditive” units had significantly weaker twitch tensions than the units which added linearly. Lengthening or shortening the whole muscle, from maximal isometric settings, reduced whole muscle twitch tension as well as muscle unit tension. Injury to the lateral rectus muscle did not significantly alter whole muscle tension. These findings suggest that the known serial and branching arrangement of these muscle fibers, as well as the complex interfiber matrix, may help explain the force reduction in some muscle units and the whole muscle's resistance to insult. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1229–1235, 1997