Distribution
Most skeletal muscles are a mixture of all three types of skeletal muscle fibres. About ½ of typical skeletal muscle are SO.
postural muscles of topline : high slow oxidative fibres (SO)
limbs : not only support the body but are also used for movement, have high proportions of both slow oxidative and fast oxidative-glycolytic fibres. The hind legs also function more in propulsive movements such as acceleration, jumping and rearing. Therefore, these muscles have a higher proportion of fast glycolytic fibres (FG).
Cardiac Muscle Tissue
The principle tissue in the heart wall is Cardiac Muscle Tissue. Between the layers of cardiac muscle fibres, and the contractile cells of the heart are sheets of CT that contain blood vessels, nerves, and the conduction system of the heart. Cardiac muscle fibres have the same arrangement of actin and myosin and the same bands, zones, and Z-discs as skeletal muscle fibres and use the sliding filament mechanism. However, as mentioned in previous chapters, intercalated discs are unique to cardiac muscle fibres. They are transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibres to one another. The discs contain desmosomes which hold the fibres together and gap junctions, which allow muscle action potentials to spread from one cardiac muscle fibre to another. Cardiac muscle has an endomysium and perimysium but lacks an epimysium.
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