Which of the following is known as the natural pacemaker of the heart?

1.  Sino atrial node

2.  Atrioventricular node

3.  Bundle of His

4.  Purkinje fibers 

Depolarisation and repolarisation actually initiate ___________ in different chambers of heart?

(1) contraction and relaxation

(2) relaxation and contraction

(3) thickening and thinning

(4) thinning and thickening

The cardiac pacemaker in a patient fails to function normally. The doctors find that an artificial pacemaker is to be grafted in him. It is likely that it will be grafted at the site of

1.  Atrioventricular bundle

2.  Purkinje system

3.  Sinoatrial node

4.  Atrioventricular node 

Atrial systole

1.  Increases the flow of blood into the ventricles by 70 percent

2.  Is due to the generation of the action potential in AVN

3.  Increases the flow of blood into the ventricles by 30 percent

4.  Coincides with ventricular systole

The action potential causes ______ and then the ______ to undergo ______ followed by ______.

(1) ventricles, atria, contraction, relaxation

(2) atria, ventricles, contraction, relaxation

(3) ventricles, atria, relaxation, contraction

(4) atria, ventricles, relaxation, contraction