Understanding the Heart's Natural Pacemaker: The Sinoatrial Node
The sinoatrial (SA) node, a cluster of specialized cells in the right atrial wall, is the heart's primary pacemaker. It spontaneously generates electrical impulses (~60–100 bpm at rest) that initiate each heartbeat, triggering atrial contraction and then ventricular contraction via the AV node and His-Purkinje system. Autonomic nerves modulate its rate: sympathetic increases, parasympathetic (vagus) decreases.
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