AIPMT-NEET Biology Aspirants, read out the next AIPMT-NEET Biology Study material/ Notes on how the conduction system of heart works, important for AIPMT-NEET Biology.

Entire heart is made up of cardiac muscles. These cardiac muscle fibers are shorter in length and less circular than skeletal muscle fibers. They give stairs-like appearance, as cardiac muscle fiber has branches.

• Cardiac muscle fibers are self –excitable (auto-excitable), i.e. these fibers have ability to generate action potential without any external stimuli and this property of self-excitation is responsible for rhythmic electrical activity and contractions of heart. Hence, these fibers are also called as auto-rhythmic fibers.
• Let’s take a look on how the cardiac action potential travels through heart and conduction system working:

1) SA node or Sinoatrial node- it is located in the right upper corner of right atrium near the opening of superior vena cava. Nodes are also special patches of cardiac muscle fibers. Cardiac action potential is generated from SA node. SA node can generate the maximum number of action potentials, i.e., 70-75 per min. So, it is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is also called as pacemaker.

Each action potential generated from SA node travels throughout both atria via atrial muscle fibers to undergo contraction of both atria simultaneously.

2) AV node or Atrioventricular node– It is located in the interatrial septum (NCERT- lower left corner of the right atrium close to the atrio-ventricular septum). Action potential generated from SA node and conducted through atrial muscle fibers also reaches AV node.

3) Atrioventricular (AV) bundle or bundle of His – From AV node, action potential reaches bundle of nodal fibers called as AV bundle or bundle of His (named after Wilhelm His). From here only action potential can be conducted from atria to ventricles otherwise atria and ventricles are electrically insulated from each other. Then AV bundle passes through the atrio-ventricular septa to emerge on the top of the interventricular septum and immediately divides into right and left bundle branches. These branches travel through the interventricular septum, towards the apex of the heart. So, action potential reaches left and right bundle branches from AV bundle.

 4) Purkinje fibers- Left and right bundle branches give rise to minute fibers throughout the ventricular musculature of the respective sides called as purkinje fibers. These fibers conduct action potential rapidly across the ventricles leading to their contraction.

Conduction system of heart