Tension and shortening velocity of slow muscle fibers of cat extraocular muscle
Kimura, H.
Nihon Seirigaku Zasshi. Journal of the Physiological Society of Japan 42(7): 151-159
1980
ISSN/ISBN: 0031-9341 PMID: 7277241 Document Number: 161543
Tension and shortening of the extraocular muscles were investigated with the aim to evaluate the contribution of the contraction of the slow muscle fibers to that of the whole muscle. The muscle was stimulated either massively (massive stimulation) or at one end (point stimulation). When the muscle was stimulated at one end, the slow muscle fiber would not develop the tension. Let the tension developed by the massive stimulation be M and that by the point stimulation be P, then (M-P)/M, slow fiber ratio, would indicate the degree of contribution of slow muscle fiber to the whole muscle. The slow fiber ratio in tetanus was, 8.1-23% for the inferior oblique muscle, 24-30% for the lateral rectus muscle and less than 5% for the retractor bulbi muscle. The shortening velocity under a small load was independent of the mode of stimulation. The evidence indicates that the resting slow muscle fibers do not act as the resistance against the shortening of the twitch muscle fibers. When the inferior oblique or lateral rectus muscle was stimulated for long time, the tension showed two peaks. The interval between them was 6-10sec and the amplitudes were nearly comparable.