STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Heart muscle fibres. Coloured scanning electron micrograph (SEM) of cardiac muscle fibrils (pink) from a healthy heart. 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. Magnification: x800 when printed 10 centimetres wide.
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