SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Cardiac muscle. Coloured scanning electron micrograph (SEM) of healthy heart (cardiac) muscle fibrils (yellow). Mitochondria (red) supply the muscle cells with energy. The muscle fibrils, or myofibrils, are crossed by transverse tubules (thin lines). These tubules mark the division of the myofibrils into contractile units (sarcomeres). Cardiac muscle is under subconscious control and continuously contracts to pump blood around the body without tiring. Magnification: x1665 when printed 10cm wide.
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