Muscle fibre types

Voluntary muscles contain a variety of fibre types which are specialized for particular tasks. Most muscles contain a mixture of fibre types although one type may predominate. All human skeletal muscles are composed of several different muscle fibre types. Up to seven different fibre types have been identified histochemically based on the pH stability of myofibrillar adenosine triphosphatase and on the myosin heavy chain profile. Innumerable fibre type transients exist due to continuing adaptation processes. However, three main... 

Table 13.2 Properties of human muscle fibre types and their capacities for fuel utilisation ...

Calvo, J. and Johnston, I.A. (1992). Influence of rearing temperature on the distribution of muscle fibre types in the turbot, Scophthalmus maximus, at metamorphosis. Journal of Experimental Marine Biology and Ecology 161,45-55. 

Mosse, P.R.L. and Hudson, R.C.L. (1977). The functional roles of different muscle fibre types identified in the myotomes of marine teleosts a behavioural, anatomical and histochemical study. Journal of Fish Biology 11,417-430. 

The different muscle fibre types of fish may be cited as examples of tissues with widely differing fractional protein synthesis rates cardiac muscle has often been found to have fractional protein synthesis rates which are approximately four fold higher than those of white muscle fibres (Haschemeyer et al. 1979 Smith et al. 1980 Fauconneau 1985 Houlihan et al. 1986 Houlihan et al. 1988b McMillan and Houlihan 1988). 

The function of muscle is to generate a force on contraction, either to maintain or change the position of a joint. There are two main types of muscle fibres Type 1 (slow twitch), which allow sustained low energy contraction, and Type 2 (fast twitch), which allow rapid forceful contractions. Muscles are comprised of varying proportions of both types of fibres. Postural muscles are composed mainly of Type 1 fibres, with a predominantly linear arrangement of fibres, whereas non-postural muscles... 

By selecting specific muscle types the authors were able to separate different myofibrillar protein types slow-contracting, fast-contracting and heart. Since each muscle fibre type contains its own specific myosin chain, the gelation properties of fractions prepared from them vary. In fact, most muscles contain a mixture of both types of myosin, as well as a third (fast-contracting) type. Salt was required to produce gels however, once... 

Salmons S, Gale DR, Sreter FA. Ultrastructural aspects of the transformation of skeletal muscle fibre type by long-term stimulation changes in Z discs and mitochondria. J Anat 1978 127 17-31. 

Handel, S.E. and N.C. Stickland, 1987b. The growth and differentiation of porcine skeletal muscle fibre types and the influence of birthweight. J. Anat. 152, 107-119. 

Martin, W., S. Murphree and J. Saffitz, 1989. Beta-adrenergic receptor distribution among muscle fibre types and resistance arterioles of white, red, and intermediate skeletal muscle. Circul. Res. 64, 1096-1105. 

In the periphery at the mammalian neuromuscular junction each muscle fibre is generally influenced by only one nerve terminal and the one NT acts on one type of receptor localised to a specific (end-plate) area of the muscle. The system is fitted for the induction of the rapid short postsynaptie event of skeletal muscle fibre contraction and while the study of this synapse has been of immense value in elucidating some basic concepts of neurochemical transmission it would be unwise to use it as a universal template of synaptic transmission since it is atypical in many respects. 

Second, as in the ventricular muscle fibres of the heart, opening of L-type channels can generate sustained plateau potentials following the initial Na +-mediated action potential — for example, in the rhythmically firing neurons of the inferior olive (Fig. 2.7). 

In contrast, skeletal muscle contraction is more rapid than that of smooth muscle but skeletal muscle cannot maintain the same tone for long periods of time. As indicated in Table 7.1, we can distinguish sub-types of muscle fibre within... 

Those athletes who are genetically adapted to become very muscular -weightlifter types and body builders - are likely to have 40% Type I and 60% Type II whereas those destined to become great endurance athletes probably have 60 80% Type I and 20 0% Type II muscle fibres. 

During aerobic exercise when the primary muscle fibres being utilized are Type I, FFA are used even in the presence of adequate glucose. Generally during activities of intensity between 60 and 75% max heart rate the primary muscles used are Type I. As intensity increases (to 75-85%), Type Ila come into play more and more and they utilize glucose as their source of energy these... 

Failure of mitochondria to oxidise fatty acids snfficiently rapidly reduces the ability of the muscle fibres and other cells to utilise fat after a meal, so that fat levels in the blood and in the muscle increase to abnormally high levels. Over a period of time, this disturbance can lead to obesity or type 2 diabetes meUitus (Chapter 9). 

They cannot be oxidised if the tissue lacks mitochondria, e.g. red blood cells, kidney medulla, lens of the eye, type IIB muscle fibres (anaerobic fibres) - see Chapfer 6. 

For some cells or tissues, very little of the glucose or glycogen is fully oxidised so that most of the ATP is generated from the conversion of glucose or glycogen, via glycolysis, to lactate. These include erythrocytes, type llx muscle fibres and epidermal cells in the skin. Type llx fibres appear to be specific to humans since they possess almost no mitochondria. 

Type I is also known as slow twitch fibre. Type llAis also known as fast twitch, and fibre type IIB is also known as fast twitch. Data are from world-class athletes and from fibres in the quadriceps muscle. 

Researchers have been dogged by the inability to delineate between myoactivity and neuroactivity, mainly because the isolation of individual tissues by dissection is extremely difficult. This obstruction precipitated the development of methods to generate dispersed muscle fibres, and these preparations provided the first visual information on individual muscle fibres and/or muscle fibre bundles three morphologically distinct fibre types were recorded from Schistosoma mansoni, frayed, spindle-shaped and crescent-shaped fibres (Day et al., 1993). Although the location of all three fibre types within the worm is not clear, it has been suggested that the frayed fibres originate from the longitudinal muscle layer. 

Usually known as mosaic muscle in these fish, as the white muscle fibres are interspersed with individual red muscle cells (Walker and Emerson, 1978 Johnston, 1982). This mixed type of muscle is not considered in detail here. 

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