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Conduction System of the Heart

Definition
An intrinsic system of stimulation to contract.
Small groups of specialized neuromuscular cells in the myocardium.
They initiate and conduct impulses  
coordinated and synchronized contraction of the heart muscle.
Influenced by nerve impulses initiated in the brain and by circulating chemicals including hormones.

Sinuatrial node (SA node)
Specialized cell  group in the wall of the right atrium
Near the opening of the superior vena cava.
Described as 'pace-maker' of the heart

Atrioventricular node (AV node)
Specialized cell group  -  in the wall of the atrial septum
Near the atrioventricular valves.
Capable of being autonomous.

Atrioventricular bundle (AV bundle or bundle of His)
Specialized fibres
Originate from the AV node.
It crosses the fibrous ring that separates atria and ventricles
At the upper end of the ventricular septum, it divides into right and left bundle branches

Purkinje fibres
Finer branches of the bundle in the ventricular myocardium called the Purkinje fibres
AV bundle, bundle branches and Purkinje fibres convey impulses of contraction from the AV node to the apex of the myocardium and causes systole beginning from the apex