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Conduction System of Heart

Hello friends! What’s going on? I hope all will be well and happy! Today we are discuss about Conduction System of Heart which initiate the normal Cardiac cycle.

The specialized myocardial tissue which initiates and conducts the electrical impulses through out the heart which causes the contraction of heart.

Cardiac conduction system consist of:
  • Sinoatrial node
  • Atrioventricular node
  • Atrioventricular node
  • Atrioventricular bundle (bundle of His)
  • Purkinje fibres
  • Sinoatrial node-Auto rythmic
During the contraction of the heart muscle following events are proceed:

  • Sinoatrial(SA) node creates an excitation signal(an action potential).
  • Excitation wave spreads across the atria causing them to contract.
  • After reaching the Atrioventricular (AV) node, the signal is delayed.
  • It is the conducted into the bundle of His, and down the interventricular septum.
  • The bundle of His and the Purkinje fibres which spread the wave impulses along the ventricles and causes to contact them.
Components of the Cardiac Conduction System :

Sinoatrial Node:

  • It is the Auto rhythmic node which generates an Action Potential w/o nervous input.
  • These are specialised cells(pacemaker cells), and which is present in the upper wall of right atrium, at the junction superior vena cava enters.
  • This pacemaker cells generate electrical impulses.
  • The wave of excitation created bye the Sinoatrial Node through gap junction across both atria, resulting in atrial contraction (atrial Systole).with blood moving from the atria into the verticals
The rate at which the SA node generates impulses in influenced by the autonomic nervous system is given below :

Sympathetic nervous system :

It increase the rate of SA node, and it increase the heart rate.

Parasympathetic nervous system :


It decrease the fire rate of SA node, and also decrease the heart rate.

Atrioventricular Node :


Atrioventricular node present between the Atrioventricular septum, and which near to the opening of coronary sinus.

The Atrioventricular node acts to delay the impulses upto 120ms,to ensure the atria take enough time to fully eject blood into the ventricles before ventricular systole.
The excitation wave passes from Atrioventricular node into the Atrioventricular bundle.

Atrioventricular Bundle:


The Atrioventricular bundle is a of His which is continue as a specialised tissue of AV node, and serves to pass the electrical impulse from the AV node to the Purkinje fibres of the ventricles.

It descends down into the membranous part of the interventricular septum. It is bundles before dividing into two main
Right bundle branch:It conducts the impulse into the Purkinje fibres of right ventricle.
Left bundle branch :
It conducts the impulse into Purkinje fibres of the left ventricle.

Purkinje fibres:

  • Ultimately, atria contract FIRST FOLLOWED By Ventricles (contract from bottom up to sequence blood up and OUT). They are abundant fibres with glycogen and have extensive gap junctions.
  • These cells are present in the inner ventricular walls of the heart, and these cells are sends the cardiac action potentials from the Atrioventricular bundle to the myocardium of the ventricles.
  • This rapid conduction allows the Co-ordinated ventricular Contraction (ventricular systole) and blood is pass through right and left ventricles to the pulmonary artery and aorta respectively.
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