Question

What is the significance of atrioventricular node and atrio-ventricular bundle in the functioning of heart?

Answer 1

Hint: Heart has the ability to contract at a regular interval of time. This is the rhythmic contractile activity of the heart.
- Antrio-ventricular nodes and atrio-ventricular bundles maintain this rhythmic automatic contractile activity of the heart. Ventricular bundles maintain this rhythmic automatic contractile activity of the heart.

Complete Answer:
- Components of the conduction system are – sino-atrial node (SAN), atrioventricular node (AVN), atrioventricular bundle (Bundle of His) and Purkinje fibers.
- A specialized cardiac musculature called the nodal tissue is distributed in the heart.
- A patch of this tissue is present in the right upper corner of the right atrium called sino-atrial node (SAN).
- Another mass of this tissue is seen in the lower left corner of the right atrium close to atrio-ventricular septum is called Atrio-ventricular node (AVN).
- A bundle of nodal fibres, atrio-ventricular bundle (AV bundles) continue from the AVN which passes through the atrio-ventricular septa to emerge on the top of the interventricular septum and immediately divides into right and left bundle.
- These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called purkinje fibres. These fibres along with left and right bundles are known as bundles of His.
- The nodal musculature has the ability to generate action potentials without any external stimuli i.e. it is called autoexcitable.
- Stimulation from SA nodes causes both of the atria to contract at the same time because the muscle tissue conducts the stimulation rapidly.
- As a wave of stimulation (depolarization) spreads across the atria resulting in their contraction, due to this AV node also becomes stimulated (depolarized). It conducts action potential slowly to the ventricles then bundle of His transmits impulse from AV node to the ventricle through purkinje fibres.

Hence, it is called a Pacemaker.

Note: SAN is called a Pacemaker. Our heart normally beats $70 - 75$ times in a minute. Average rate is $72$ beats/min. It is responsible for initiating and maintaining the rhythmic contractile activity of the heart.