The sinoatrial node (SA node), rarely also spelled sinuatrial node, is a group of specialized pacemaker cells that controls the rate of the heart.
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Summary
location: upper wall of the right atrium, at the junction where the superior vena cava enters
blood supply: sinoatrial nodal artery
innervation: sympathetic and parasympathetic branches
Gross anatomy
The sinoatrial node is located in the upper wall of the right atrium, deep to the epicardium at the junction where the superior vena cava enters, near the sulcus terminalis. It is a collection of pacemaker cells that generates impulses at a rate of approximately 60-100 beats per minute at rest 1, and sets the underlying heart rate 2,3.
These pacemaker cells spontaneously generate electrical impulses that extend across the gap junctions to both atria, causing atrial contraction 4.
The rate at which the sinoatrial node generates impulses is influenced by the autonomic nervous system:
sympathetic nervous system: increases the firing rate of the SA node and thus increases the heart rate
parasympathetic nervous system: decreases the firing rate of the SA node decreases and thus decreases the heart rate
History and etymology
The sinoatrial node was first described by Arthur Keith and Martin Flack in 1906 4.
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