title: Highly extensible skeletal muscle in snakes.
abstract: Many snakes swallow large prey whole, and this process requires large displacements of the unfused tips of the mandibles and passive stretching of the soft tissues connecting them. Under these conditions, the intermandibular muscles are highly stretched but subsequently recover normal function. In the highly stretched condition we observed in snakes, sarcomere length (SL) increased 210% its resting value (SL0), and actin and myosin filaments no longer overlapped. Myofibrils fell out of register and triad alignment was disrupted. Following passive recovery, SLs returned to 82% SL0, creating a region of double-overlapping actin filaments. Recovery required recoil of intracellular titin filaments, elastic cytoskeletal components for realigning myofibrils, and muscle activation. Stretch of whole muscles exceeded that of sarcomeres as a result of extension of folded terminal tendon fibrils, stretching of extracellular elastin and independent slippage of muscle fibers. Snake intermandibular muscles thus provide a unique model of how basic components of vertebrate skeletal muscle can be modified to permit extreme extensibility.
authors.affiliation: Department of Biological Sciences, 1 W. Packer Avenue, Lehigh University, Bethlehem, PA 18015, USA Biology Department, Radford University, Box 6931, Radford, VA 24142, USA mclose2@radford.edu.
authors.forename: Matthew
authors.initials: M
authors.lastname: Close
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104-6058, USA Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA.
authors.forename: Stefano
authors.initials: S
authors.lastname: Perni
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104-6058, USA.
authors.forename: Clara
authors.initials: C
authors.lastname: Franzini-Armstrong
authors.affiliation: Department of Biological Sciences, 1 W. Packer Avenue, Lehigh University, Bethlehem, PA 18015, USA.
authors.forename: David
authors.initials: D
authors.lastname: Cundall
mesh_terms: D008841:Actin Cytoskeleton / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D003599:Cytoskeleton; D008334:Mandible; D018482:Muscle, Skeletal / Q000502:physiology* / Q000648:ultrastructure*; D009210:Myofibrils / Q000502:physiology* / Q000648:ultrastructure; D012518:Sarcomeres / Q000502:physiology* / Q000648:ultrastructure; D012911:Snakes / Q000502:physiology*
keywords: Comparative myology; Gape; Intermandibular soft tissues; Macrostomy; Passive extensibility; Titin