Question

Choose the correct statement(s) about SA node.
I. Located at lateral wall of the right atrium.
II. It initiates the rhythmic contractile activity of the heart and maintains it.
III It is called pace keeper of the heart.
IV. It directly passes on the impulses to the Purkinje fibres.

• A. All except III
• B. I and II
• C. Only I
• D. All except IV

Answer 1

The correct option is B I and II

Sino atrial node or SA-node is located in the lateral wall of the right atrium near the opening of the superior vena cava. Thus statement I is correct.

The waves of cardiac muscle contraction originate from the SA node and reach the AV-node which is situated at the base of the right auricle. The excitatory impulses from the AV node are rapidly transmitted to the bundle of His which lies in the interauricular and interventricular septum. From the bundle of His it spreads throughout the walls of the ventricles via the Purkinje fibres. Thus Statement II is correct but IV is incorrect.

SA node is called the pacemaker of the heart (not pace keeper) because it is the site at, which the initiation of the contraction originates. Thus statement III is incorrect.