title: Physiology of the sternoradialis muscle: sexual dimorphism and role in amplexus in the Leopard frog (Rana pipiens).
abstract: 1. The role of upper arm muscles in amphibian amplexus was investigated. 2. The musculature of the male frog is arranged so that the response to any form of massive stimulation is flexion of the forelimbs, the fundamental pattern in amplexus. 3. The sternoradialis, one of the forelimb flexors, exhibited several sexually dimorphic characters. It was found to be larger in males than females and possessed a large population of small diameter muscle fibers. 4. Mechanical evidence indicated that the male sternoradialis contains a significant number of tonic or slow muscle fibers. These tonic fibers undergo physiological changes during amplexus including a membrane potential shift in the direction of the mechanical threshold and greater efficiency of contraction. 5. It was concluded that the sternoradialis contributes significantly to muscular response in amplexus and that the tonic fibers in this muscle play an important role in amplexus.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D005552:Forelimb; D008297:Male; D008564:Membrane Potentials; D009132:Muscles / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*; D011187:Posture; D011894:Rana pipiens / Q000502:physiology*; D012737:Sex Factors; D012726:Sexual Behavior, Animal
chemical_list: D000109:Acetylcholine; D002118:Calcium