Principles of Construction and Function

1 Principles of Construction and Function Coarse and Fine Structm-es Crossections 

Characteristic, categorizable elements can be seen upon cutting across any skeletal muscle, such as musculus biceps brachii (the biceps). A closer look reveals finer and finer structures. Each hatched or shaded element of Fig. 9.1 in the lower sketch of this figure, respectively, is presented in more detail in a hierarchical fashion. 

The muscle is several centimeters in diameter. It works within a relatively stiff sheath of connective tissue, the fascia, from which the muscle is separated by a layer of loose connective tissue. The muscle is divided into bundles of muscle fibers by internal boundaries (perimysimn). 

Such a muscle fiber bundle has a diameter of about one centimeter. The fiber bundle consists of a series of muscle fibers, each enveloped in a fiber sheath and held apart from the others by a loose connective tissue, permitting relative motion during muscle contraction. 

The muscle fiber is formed in ontogeny (individual development) as a fusion of single cells to form a sort of giant polynucleate cell. Its thickness is no greater than 100 pm. The partially aqueous interior medium contains bimdles of myofibrils in addition to nuclei and mitochondria (cellular power plants). 

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