Meeting Abstract
Hollow, cylindrical body plans and obliquely striated muscles are characteristic of soft-bodied invertebrates, and both affect the biomechanics of locomotion and movement in these diverse animals. We highlight two different aspects of functional heterogeneity in obliquely striated muscles, one driven by animal shape and size, and the other driven by the intrinsic mechanical properties of the fibers. First, we show how a hollow, cylindrical shape in cephalopod molluscs causes significant non-uniformities in muscle strain across the body wall, and describe the implications for the length-force relationship of the obliquely striated muscles that power movements in these animals. Moreover, we show how these non-uniformities increase in magnitude as body wall proportions change during growth and development. Second, it has been assumed for decades that oblique striation permits relatively high force output over an extraordinary range of muscle lengths. Recent work in molluscs and annelids, however, has revealed remarkable diversity in the contractile properties of obliquely striated fibers, thus calling this assumption into question. We describe how the length-force relationship (LFR) of cephalopod obliquely striated body wall muscles varies with position to accommodate non-uniformities in strain, and show how the LFR differs from that assumed for obliquely striated fibers. We also present data on diversity in the LFR of cephalopod and annelid obliquely striated muscles, and show that length-dependent activation in some of these fibers is completely different than that described for the skeletal fibers of vertebrates.
