SA Node Cell Population 2D: Coupled Pacemaker Entrainment

The sinoatrial node is not one clock — it is a few thousand pacemaker cells, each with its own slightly different intrinsic rate, that stay in lock-step only because gap junctions electrotonically couple their neighbours together. This top-down 2D simulator models that population directly: roughly 110 individual pacemaker cells, each running its own diastolic-depolarization physiology with realistic cell-to-cell heterogeneity, coupled through distance-delayed pulse coupling at the node's real slow conduction velocity. Turn electrotonic coupling down and watch the cells desynchronize into independent, chaotic rhythms; turn it up and watch them entrain into one coherent heart rate — while vagal tone, sympathetic tone and respiratory sinus arrhythmia reshape that rate exactly as they do in the whole heart, and the leading pacemaker site shifts under autonomic control.