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Effects of nerve cross‐union on fast‐twitch and slow‐graded muscle fibres in the toad
Author(s) -
Close R.,
Hoh J. F. Y.
Publication year - 1968
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1968.sp008596
Subject(s) - sartorius muscle , isometric exercise , chemistry , anatomy , fast twitch muscle , toad , motor nerve , muscle contracture , muscle contraction , skeletal muscle , biology , medicine , endocrinology
1. A method is described for resolving isometric tetanic tension developed by fast‐twitch and slow‐graded components of heterogeneous toad muscles. This makes use of the difference in threshold for excitation of low threshold nerve fibres which normally innervate the fast‐twitch muscle fibres and high threshold nerve fibres which innervate slow‐graded muscle fibres. 2. The sartorius muscle contains only fast‐twitch muscle fibres whereas the posterior semitendinosus (PST) contains both fast‐twitch and slow‐graded muscle fibres, the latter contributing 10‐15% of the maximum isometric tetanic tension. 3. Following surgical cross‐union of nerve to sartorius and PST muscles, both the fast‐twitch and slow‐graded muscle fibre components of the PST are reinnervated by low threshold nerves originally innervating sartorius fast‐twitch fibres, and sartorius fast‐twitch muscle fibres are reinnervated by both low threshold and high threshold nerves formerly supplying the fast‐twitch and slow‐graded muscle fibre components of the PST. 4. The characteristic mechanical responses of fast‐twitch muscle fibres and slow‐graded muscle fibres were not transformed up to 134 and 200 days respectively following nerve cross‐union. 5. PST nerve partially innervated the sartorius muscle whereas sartorius nerves completely innervated the PST muscle. Isometric tetanic tension declined markedly during repetitive indirect stimulation of cross‐innervated sartorius muscles, whereas the tetanic contractions of cross‐innervated PST showed a plateau of tension and resembled the response of normal muscles. 6. Normal, cross‐innervated and self‐innervated PST muscles gave sustained contractures in the presence of acetylcholine whereas PST muscles denervated for 120 days gave phasic contractures similar to those of normal, cross‐innervated and self‐innervated sartorius muscles.