Question

Which of the following had the job of slowing conduction of the impulses from the atria to the atria to contract and empty their blood volume into the ventricles?

Answer 1

• The conduction normally begins in the sinoatrial node (SA) node. It is located in the right atrial wall at the junction of superior vena cava and the right atrium. It is also referred as the primary pacemaker.
• The pacemaker action potential from the SA node propagates throughout both atria via gap junctions in the intercalated discs of atrial muscle fibers. Following this the atria contract.
• Then the impulses are passed through the AV node. AV node is a group of specialized muscle cells which is located near the tricuspid valve of the right atrium.
• AV node delays the impulse of 0.1 seconds whereby the atria empties the blood completely before the ventricles contract.
• Then the conduction enters the atrioventricular(AV) bundle (also known as the bundle of His), where the impulses conduct from atria to the ventricles.
• The bundle of His divided into the right bundle (conducting to the right ventricle) and left bundle branches (conducting to the left ventricle) and extend through the interventricular septum toward the apex of the heart. Left bundle further bifurcates into left anterior and left posterior bundle branches and conduction system reaches the Purkinje fibers. At this stage, the ventricular contraction occurs which pushes blood upward toward the semilunar valves and forced blood either from the right ventricle (pulmonary circulation) or from the left ventricle (systematic circulation).

Note: In Normal circumstances, the SA node has the highest impulses of 40 - 60 per minute, and the AV node has the impulse rate of 30 - 40 per minute. If any malfunctions in the SA node then the AV node takes the function of pacemaker so the heart has a lower rate.