STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Cardiac muscle. Coloured scanning electron micrograph (SEM) of cardiac muscle fibrils (green and brown) from a healthy heart. Mitochondria (pink) supply the muscle cells with energy. The muscle fibrils, or myofibrils, are crossed by transverse tubules (vertical 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.
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