Gradients of Strain in the Hollow, Cylindrical Muscular Organs of Soft-bodied Invertebrates
The current paradigm of striated muscle function assumes that all muscle fibers within a single muscle shorten the same amount and produce the same force during a given behavior. I tested a mathematical model that predicts large and non-uniform length changes (i.e., strain) in the circumferential muscle fibers of cylindrical muscular organs, such as the mantle of squid. Sonomicrometry was used to measure dimensional changes in the mantle of adult Long-finned (Doryteuthis pealeii) and Oval (Sepioteuthis lessoniana) squid; videography and morphometric analyses were used in tandem to measure dimensional changes in the mantle of D. pealeii hatchlings. These experiments supported the predictions of the model, revealing (1) the existence of a gradient of strain (i.e., the fibers near the inner surface of the mantle experienced greater strain than those near the outer surface for a given mantle contraction) and a gradient of strain rate; (2) that the magnitude of the gradients of strain (for all animals tested) and strain rate (for adults and juveniles only) increased as jet amplitude increased; (3) and that the magnitude of the gradient of strain and strain rate increased with increasing relative mantle wall thickness, as occurs during growth. These findings challenge current theories of striated muscle function and call for a reanalysis of the evolution of muscle structure and function in cylindrical muscular organs.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2010
- F&M Theses Collection