[CVS] Q.11) What is AV nodal delay? Give its causes and importance:

Ans.
Definition: AV node is responsible for the delay in transmission of impulse generated in SA node. This delay in impulse transmission is called AV nodal delay. It is about 0.09 second.
Causes:

1. Junctional fibers of AV node are very small in size.
2. Resting membrane potentials of these fibers are much negative than the normal resting membrane potential of cardiac muscle.
3. Very few gap junctions connect the successive fibers in the pathway, so that there is great resistance to the conduction of excitatory ions from one fiber to the next.
4. Prolonged refractory period of AV node.

Importance:
For this delay, the atria get time to empty their content (blood) into the ventricles before ventricular contraction begins.