The mammalian sinoatrial node
TL;DR
Mammalian hearts survive through hierarchical backup pacemakers: SA node (60-100 BPM), AV node (~40 BPM), Purkinje fibers (20-40 BPM).
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Comprehensive review of sinoatrial node function demonstrating how distributed pacemaker cells create robust cardiac rhythm control with built-in redundancy - a biological model for distributed organizational systems.
Key Findings from Opthof (1988)
- SA node contains heterogeneous population of a few hundred to a few thousand pacemaker cells
- Primary pacemaker fires at 60-100 BPM; AV node backup at ~40 BPM; Purkinje backup at 20-40 BPM
- Cat SA node showed normal function with myocytes occupying less than 5% of node volume
- Earliest discharge restricted to one site in rabbit, guinea pig, cat, and pig
- Multiple conduction pathways provide redundancy within and beyond the SA node
- First published in Cardiovascular Drugs and Therapy, Volume 1, pages 573-597