Morphofunctional and phylogenetic relations in helical muscles

Abstract

Abstract The distribution of obliquely (helical) and cross-striated muscles, and their physiological and mechanical properties, are analyzed throughout the zoological scale in relation to the presence and the functional requirements of different types of skeletal systems. It is suggested that helical fibres are an evolutionary answer to the appearing of the hydroskeleton, being able to develop high active tensions also in conditions of superelongation. The mechanism by which this unique property is realized depends on the possibility of a typical change in the relationships between thick and thin filaments of the same sarcomere.