STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Heart muscle. Transmission electron micrograph (TEM) of a longitudinal section through healthy heart (cardiac) muscle. Large oval mitochondria lie between the muscle fibres (pink). The thick transverse bands on the fibres are Z lines, regions with a more dense arrangement of actin, one of the two types of muscle filament. In order to beat, the heart produces regular electrical impulses causing the muscle filaments to slide over one another and contract the cardiac muscle. The high concentration of mitochondria reflects the large respirational demands of the heart. Magnification unknown.
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