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sarcomere
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Diagram showing the structure of striated muscle at the myofilament level, with thick myosin filaments, thin actin filaments, crossbridges, Z lines, and one sarcomere labeled. Diagram showing the structure of human striated or skeletal muscle, with labeled cross-sections from whole muscle to fascicle, muscle fiber, myofibril, and sarcomere, highlighting actin and myosin filaments.
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sarcomere

physiology
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Diagram showing the structure of striated muscle at the myofilament level, with thick myosin filaments, thin actin filaments, crossbridges, Z lines, and one sarcomere labeled.
myofilaments in a striated muscle Figure 2: The arrangement of the myofilaments in a striated muscle. The muscle is extended in the upper diagram and contracted in the lower one. The thick filaments are 1.6 micrometres (0.0016 millimetre) long in vertebrate striated muscle but up to six micrometres long in some arthropods.

A sarcomere is the fundamental contractile unit of striated muscle cells, such as those in skeletal and cardiac muscle. These repeating subunits are composed of protein filaments, primarily actin and myosin.1

During muscle contraction, sarcomeres shorten. This occurs as the actin filaments slide toward the center of a central myosin filament. This sliding filament mechanism is crucial for muscle physiology. The coordinated shortening of numerous sarcomeres within a muscle fiber leads to the overall contraction of the muscle. Actin filaments are globular proteins that polymerize to form thin filaments, while myosin forms thicker filaments. These two proteins work together, with myosin acting as a motor that moves along actin, generating the force for contraction.1234

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6 Britannica Sources
  1. sarcomere
  2. cell - Actin filaments
  3. actin: Top Questions
  4. muscle - Sliding of filaments
  5. muscle - Cross bridges
  6. muscle - The myofibril

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