Cardiac Conduction System
The cardiac conduction system is the network of specialized cardiac cells that generates the heartbeat and conducts the electrical impulse through the heart in an ordered sequence. It comprises the sinoatrial node, the atrioventricular node, the bundle of His, the bundle branches, and the Purkinje fibres, together ensuring that the atria and ventricles contract in a coordinated, timed manner.
Definition
The cardiac conduction system is the assembly of specialized myocardial structures, the sinoatrial node, atrioventricular node, His bundle, bundle branches, and Purkinje network, that initiates each heartbeat and propagates the electrical impulse through the heart in a coordinated sequence.
Scope
This entry covers the components of the conduction system, the normal sequence and timing of impulse spread, the mechanisms of cell-to-cell propagation, and the physiological role of conduction delay at the atrioventricular node. It is a physiology reference and does not provide guidance on conduction disorders.
Core questions
- What are the components of the cardiac conduction system?
- In what sequence does the electrical impulse spread through the heart?
- How does the impulse propagate from cell to cell?
- Why is there a delay at the atrioventricular node?
Key concepts
- Sinoatrial node
- Atrioventricular node and nodal delay
- Bundle of His
- Bundle branches
- Purkinje fibres
- Gap junctions and cell-to-cell coupling
- Conduction velocity
- Safety factor of propagation
Mechanisms
Each impulse normally originates in the sinoatrial node, the dominant pacemaker, and spreads across the atria. It then converges on the atrioventricular node, where conduction is deliberately slow; this delay allows the atria to finish contracting and filling the ventricles before ventricular activation. From the atrioventricular node the impulse travels rapidly down the bundle of His, into the right and left bundle branches, and out through the Purkinje fibres, which distribute excitation to the ventricular myocardium so that contraction proceeds in a coordinated, near-synchronous fashion. Propagation between cells occurs through gap junctions that electrically couple adjacent myocytes; conduction velocity and the safety factor for propagation depend on the magnitude of the depolarizing current, the passive electrical properties of the tissue, and the density and distribution of these intercellular connections.
Clinical relevance
Knowledge of normal conduction provides the framework for understanding heart block, bundle-branch patterns, and the timing relationships seen on the electrocardiogram. This entry is educational physiology and not a basis for individual diagnosis or treatment.
History
The components of the conduction system were identified in the early twentieth century: the atrioventricular bundle by Wilhelm His Jr., the atrioventricular node and conducting network by Sunao Tawara, and the sinoatrial node by Arthur Keith and Martin Flack. Later cellular and molecular studies, summarized in modern reviews, clarified how impulse propagation depends on gap-junction coupling and tissue architecture.
Key figures
- Wilhelm His Jr.
- Sunao Tawara
- Arthur Keith
- Martin Flack
- Andre Kleber
- Yoram Rudy
- Glenn Fishman
Related topics
Seminal works
- park-fishman-2011
- kleber-rudy-2004
- boyett-2000
Frequently asked questions
- Why is conduction slow at the atrioventricular node?
- The slow conduction introduces a brief delay between atrial and ventricular activation, allowing the atria to complete filling of the ventricles before they contract; it also limits how fast impulses can pass from atria to ventricles.
- What is the role of the Purkinje fibres?
- The Purkinje network conducts the impulse rapidly through the ventricles, distributing excitation so that the ventricular muscle contracts in a coordinated, nearly simultaneous manner.