MusFIG 8: Structure of the platymyarian obliquely striated muscle.

A. Schematic diagram of a body wall muscle cell. Rows of dense bodies (dots) and A bands (thin lines) give the striated appearance macroscopically. Attachment plaques are localized at the end of the terminal half I bands, where the muscle cells in a quadrant contact one another. (Top inset) Layers of tissue from outside (cuticle, top) to inside (muscle, bottom). (Bl) Basal lamina between muscle and hypodermis (Hyp).
B. Schematic diagram of a wedge of the myofibrillar portion and the muscle belly. The nucleus and the organelles are located within the muscle belly. The myofilament lattice is arranged as a sheet of filaments on the side of the muscle cell that apposes the hypodermis. Contractile units are in register longitudinally; however, they are placed in tandem horizontally, giving rise to an alternating pattern of thick (small yellow dots and lines) and thin filaments (small black dots and lines) bands. The thin filaments are omitted from the lateral and top sides of the drawing. (DB) Dense body.

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