JEANETTE ENGQVIST / SCIENCE PHOTO LIBRARY JEANETTE ENGQVIST / SCIENCE PHOTO LIBRARY
Electrical conduction system of the heart. Computer illustration showing the impulse conduction system (yellow) and nodes (bulb-shaped, yellow) of the human heart. The sinoatrial (SA) node's (upper left) self-excitatory muscle cells trigger an impulse that spreads through the heart's upper chambers (atria) to the atrioventricular (AV) node (centre left). Contraction of the atria causes blood to move into the heart's lower chambers (ventricles). Nerve extensions (yellow, forked, bottom) via the bundle of His cause the ventricles to contract, sending blood to the lungs and to the rest of the body.
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