Slow Muscle Fibres

Abstract

The discussion how mammalian muscle fibres could be subdivided into fibre types was provoked not only by observations on red and white mammalian muscles (see Chap. D) but also by the fact that amphibia have some muscles with outstanding functional properties. These muscles contract slowly, and respond with lasting contractions to acetylcholine and not, like twitch muscles, with short and rapid contractions, or with series of contractions (Sommerkamp 1928).The occurrence of slow-tonic muscles is related to the specific motor behavior of the animals (Wacholder and Von Ledebur 1930). Krüger (1929) found that the “tonic” muscles contain a minority of fibres which in cross-sections display ribbon-shaped myofibrils; he postulated that these fibres were the specific tonic (slow) fibres and named them “Felderstruktur” fibres in contrast to phasic (twitch) “Fibrillenstruktur” fibres. Fibrillenstruktur refers to the dotted appearance of the fibres in cross-sections. The Felderstruktur fibres carry several nerve endings each resembling a bunch of grapes (terminaisons en grappe, Tschiriew 1879); the Fibrillenstruktur fibres have one or a few solid endplates (terminaisons en plaque, Tschiriew 1879) (Krüger 1952). The different innervation pattern is also described as “multiple” and “focal”, respectively.