DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Capillary from heart muscle, coloured scanning electron micrograph (SEM). Red blood cells are tightly packed in the capillary. Note the small Purkinje fibre on the surface of the capillary. Purkinje fibres are modified cardiac muscle fibres which originate from the atrioventricular node and spread into the two ventricles. They transmit the electrical impulse from the atrioventricular node to the ventricles enabling their almost simultaneous contraction. The spread of excitation through the ventricles from the atrioventricular node is extremely rapid, moving at one to four meters per second. Magnification: x800 when shortest axis printed at 25 millimetres.
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