THOMAS DEERINCK, NCMIR / SCIENCE PHOTO LIBRARY THOMAS DEERINCK, NCMIR / SCIENCE PHOTO LIBRARY
Cardiac muscle. Coloured transmission electron micrograph (TEM) of cardiac muscle fibrils (orange and blue)from a healthy heart. Mitochondria (red) supply the muscle cells with energy. The muscle fibrils, or myofibrils, are crossed by transverse tubules (narrow dark blue lines). These tubules mark the division of the myofibrilsinto contractile units (sarcomeres). In the centre is an intercalated disc (strong, undulating dark blue line). Intercalated discs are double membranes that separate adjacent cells in the muscle fibres. They facilitate synchronised contraction of the muscle. Cardiac muscle is under subconscious control and continuously contracts to pump blood around the body without tiring. Magnification: 3000x when printed 10 centimetres across.
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