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The sinuatrial node, is also known as the "sinoatrial node", "SA node" or by its eponym, the "node of Keith and Flack". It is the initial component of the conduction system of the heart. It is a small nodule of cardiac muscle tissue, somewhat horseshoe-shaped that is found at the junction of the superior vena cava and the right atrium. Because of the inherent automaticity and rhythmical contractions of the SA node, it acts as the main pacemaker of the heart, being the base for normal heart beat, also known as "sinus rythm" It receives blood supply from the SA node artery, usually the first or second branch that arises off the right coronary artery. The SA node artery is a long vessel that passes between the right atrium and the ascending aorta on its way to the SA node. |
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| The SA node receives innervation from both sympathetic and parasympathetic nerves. The parasympathetic innervation is by way of the vagus nerve, the Xthcranial nerve. The sympathetic innervation is by way of the cardiac nerves, a plexus that has its origin in the ventral ramiof the first four thoracic spinal nerves (T1-T4).
The SA node was discovered in 1906 by Martin W. Flack (1882-1931) and Arthur Keith (1866-1955). They named it originally the sinoauricular node. Click on the image for a larger version. Image modified from the original: "3D Human Anatomy: Regional Edition DVD-ROM." Courtesy of Primal Pictures |
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