DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Brightfield light micrograph of human cardiac muscle. Cardiac muscle consists of branching elongated muscle cells, called myocytes, which form fibres (blue vertical muscle bundles). The myocytes are separated by intercalated discs (pink), which allow electrical signals to travel rapidly between myocytes. Myocytes consist of microfilaments (myofibrils) of the contractile proteins actin and myosin, many mitochondria (not seen) and centrally located nucleus (not seen). Cardiac muscle is myogenic, it can cause its own contraction without any other input. Cardiac muscle, unlike skeletal muscle, is composed of separate cellular elements. The heart produces regular electrical impulses causing the muscle myofibrils to slide over one another and contract the cardiac muscle. In the living heart connective tissue rich in blood fills the spaces between the muscle cells bands demonstrating the heart's high demand for oxygen. Magnification: x100 when shortest axis.
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