Question

Which of the following statements are correct?
I. Bundle of His originates from the SA-node.
II. SA- node is situated in the wall of the right atrium.
III. Atrial contraction stimulates the AV-node.
IV. AV-node sets up the cardiac impulses 72 times per minute.

• A. I, II, and III are correct
• B. I and II are correct
• C. II and IV are correct
• D. II and III are correct

Answer 1

The correct option is D II and III are correct

• The initiation of heartbeat or the cardiac cycle begins when the deoxygenated blood enters the right atrium which stimulates the SAN to undergo depolarisation. SA- node is situated in the wall of the right atrium.
• The electrical signal travels from the SA node through muscle cells in the right and left atria. The signal triggers the muscle cells that make your atria contract. The atria contract, pumping blood into your left and right ventricles. The electrical impulse is sent from the sinoatrial (SA) node to the atrioventricular (AV) node.
• From the AVN, the bundle of His quickly transmits the impulse to the left and right bundle branches and into the ventricles through Purkinje fibres, resulting in a synchronised contraction of the ventricles.
• SAN sets up the cardiac impulse to 72 times per minute. There is an AV-nodal delay of 0.09 sec which sets the cardiac impulse to 40-60 times per minute.