Squid Cross-Striated Muscle: The Evolution of a Specialized Muscle Fiber Type
The musculature of the arms and tentacles of squid provides an opportunity to examine the specialization of muscle because these two appendage types are specialized for different types of movement and the relation between structure and function has been examined at behavioral, morphological, mechanical, ultrastructural and biochemical levels. In morphological and biomechanical studies it was shown that a specific muscle mass of the tentacles, the transverse muscle, produces the extremely rapid extension of the tentacles that occurs during prey capture. Although the gross arrangement and fiber architecture of this tentacle muscle is remarkably similar to the homologous muscle in the arms, the ultrastructure of the muscle cells of the tentacle muscle differs from that of all other cephalopod musculature. The ultrastructural characteristics of the tentacle muscle cells include transverse striation and short sarcomeres, which are indicative of specialization for fast contraction. Biochemical analysis of the myofilament proteins of the musculature of the arms and tentacles suggests little accompanying alteration of the biochemical composition of these fast contracting cells. Thus, the specialization of the muscle cells for fast contraction appears to have occurred primarily through changes in the arrangement and dimensions of the components within the muscle cells rather than through changes in their gross arrangement or biochemical composition.
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Document Type: Research Article
Publication date: September 1, 1991
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