Muscles And Locomotion

to the cuticulin envelope of the epicuticle to which they are attached by a special cement. 439

As the cuticulin layer is the first one formed during production of a new cuticle (Chapter 11, Section 3.1), attachment of newly formed fibers can readily occur. Until the actual molt, however, these are continuous with the old fibers and, therefore, normal muscle contraction is possible (Neville, 1975).

Muscles comprise a varied number of elongate, multinucleated cells (fibers) (not to be confused with the muscle attachment fibers mentioned above) that may extend along the length of a muscle. A muscle is arranged usually in units of 10-20 fibers, each unit being separated from the others by a tracheolated membrane. Each unit has a separate nerve supply. The cytoplasm (sarcoplasm) of each fiber contains a varied number of mitochondria (sarcosomes). Even at the light microscope level, the transversely striated nature of muscles is visible. Higher magnification reveals that each fiber contains a large number of myofibrils (= fibrillae = sarcostyles) lying parallel in the sarcoplasm and extending the length of the cell. Each myofibril comprises the contractile filaments, made up primarily of two proteins, actin and myosin. The thicker myosin filaments are surrounded by the thinner but more numerous actin filaments. Filaments of each myofibril within a cell tend to be aligned, and it is this that creates the striated appearance (alternating light and dark bands) of the cell. The dark bands (A bands) correspond to regions where the actin and myosin overlap, whereas the lighter bands indicate regions where there is only actin (I bands) or myosin (H bands) (Figure 14.2). Electron microscopy has revealed in addition to these bands a number of thin transverse structures in the muscle fiber. Each of these Z lines (discs) runs across the fiber in the center of the I bands, separating individual contractile segments called sarcomeres. Attached to each side of the Z line are the actin filaments, which in contracted muscle are

FIGURE 14.2. Details of a muscle fiber. [After R. F. Chapman, 1971, The Insects: Structure and Function. By permission of Elsevier/North-Holland, Inc., and the author.]
Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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