Meeting Abstract

20.2  Sunday, Jan. 4  Abdominal motor patterns in mammalian locomotion: hypaxial muscle function with and without epipubic bones REILLY, S.M.*; MCELROY, E.J.; WHITE, T.D.; Ohio University; College of Charleston; Buffalo State College reilly@ohio.edu

Recently, we have shown in marsupials that 1) all of the hypaxial layers are involved in during ventilation and that each epipubic bone is retracted like a lever by the pectineus as part of a cross-couplet pattern of primary activity in abdominal muscles that provides long-axis support of the body between diagonal limb couplets. These results are significant because they reveal that hypaxial abdominal muscles are mildly active in pressurizing the gut during resting ventilation and that, at least in marsupials, all of the abdominal hypaxials play a part in ventilation during locomotion. Historicallly the cross-couplet motor pattern appears to be related to the presence of epipubic bone levers which appear in the fossil record in concert with a large suite of unique characters that define the earliest mammals. Equally significant is the question of what happens to abdominal hypaxial function when the epipubic bones are lost in the eutherians? To expand our understanding of mammalian abdominal function we examined the generality of the cross-couplet system in a third South American marsupial and we conducted the first formal studies of abdominal motor patterns in basal placental mammals focussing on a representative rodent and insectivore These data reveal a general pattern that basal mammals apply continuous abdominal muscle tone at rest and actively exhale with abdominal muscles during locomotion and that the loss of epipubic bones is associated with a shift from the cross-couplet dominated motor pattern of marsupials to unilateral activation of abdominal muscles during locomotion.