• Highly organized bundles of actin, myosins, and other proteins in the cytoplasm of skeletal and cardiac muscle cells that contract by a sliding filament mechanism; they are composed of numerous myofilaments.
  CRISP Thesaurus
  National Institutes of Health, 2006
• The contractile element of skeletal and cardiac muscle; a long, highly organized bundle of actin, myosin, and other proteins that contracts by a sliding filament mechanism.
  Gene Ontology Dictionary
  Gene Ontology Consortium, 2021
• Long interlocking strands that make up muscle fibers.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• The long cylindrical contractile organelles of STRIATED MUSCLE cells composed of ACTIN FILAMENTS; MYOSIN filaments; and other proteins organized in arrays of repeating units called SARCOMERES.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021
• Myofibril, very fine contractile fibres, groups of which extend in parallel columns along the length of striated muscle fibres. The myofibrils are made up of thick and thin myofilaments, which help give the muscle its striped appearance. The thick filaments are composed of myosin, and the thin...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2020