CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Muscle structure. Computer artwork showing the protein structure of myofibrils and how they are bound together to form muscle fibres. From bottom: Muscle cells contain many myofibrils, organelles that are composed of units (sarcomeres, centre left) of actin and myosin bound together end to end. The myofibrils are secured at either end to the cell membrane. Many cells are then bound together to form a muscle fibre (top).
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