. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SCALLOP ADDUCTOR MUSCLE 457. FIGURE 10. Diagram of a tangential section of a cross-striated adductor muscle cell. The striated part of the adductor muscle is used for swimming and therefore, it is not surprising that it has a great deal more sarcoplasmic reticulum than the smooth muscle which is responsible for keeping the shell closed. The large amount of sarcoplasmic reticulum in the cross-striated muscle as compared to the smooth muscle of the scallop adductor corresponds to the general relationship observed among vertebr
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SCALLOP ADDUCTOR MUSCLE 457. FIGURE 10. Diagram of a tangential section of a cross-striated adductor muscle cell. The striated part of the adductor muscle is used for swimming and therefore, it is not surprising that it has a great deal more sarcoplasmic reticulum than the smooth muscle which is responsible for keeping the shell closed. The large amount of sarcoplasmic reticulum in the cross-striated muscle as compared to the smooth muscle of the scallop adductor corresponds to the general relationship observed among vertebrate muscles where the faster contracting muscles have a more elaborate and greater quantity of sarcoplasmic reticulum than slower contracting muscles (Franzini-Armstrong, 1972). In vertebrates, mononuclear presumptive myoblasts fuse with one another to form a large multinucleated cell (reviewed by Fischman, 1972). In the striated scallop adductor, fusion of myoblasts evidently does not occur as evidenced by the absence of multinucleated cells and the presence of junctions connecting the ends of the muscle cells. These junctions resemble the intercalated discs of vertebrate and invertebrate cardiac muscle (reviewed by Sanger, 1979). Similar junctions were also observed in the striated adductor muscle cells of the scallop, Aequipecten irridians (Sanger, 1979; Nunzi and Franzini-Armstrong, 1981). In contrast to vertebrate cross striated muscles, there are no invaginations of the cell surface of the scallop cross-striated muscle surface to form a transverse tubular system. The scallop adductor muscle cells are small enough that diffusion of calcium from the cell surface to the sarcoplasmic reticulum can occur without the need for a transverse tubular system. In effect, a single scallop cross-striated muscle cell corresponds to one myofibril in vertebrate skeletal muscle (Sanger, 1971). Vertebrate smooth muscle has much less sarcoplasmic reticulum than vertebrate striated muscle (De
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
