Final answer:
Action potentials cannot be conducted directly from the atria to the adjacent regions of the ventricles due to the presence of a connective tissue called the cardiac skeleton. The action potential must travel through the atrioventricular node and the Purkinje fibers to reach the ventricles.
Step-by-step explanation:
The reason why action potentials are unable to be conducted from the atria directly to the adjacent regions of the ventricles is due to the presence of a connective tissue called the cardiac skeleton. This connective tissue prevents the action potential from spreading into the ventricular myocardial cells except at the atrioventricular node (AV node).
When the action potential reaches the AV node, there is a delay of approximately 100 milliseconds, allowing the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle and then to the ventricles. This delay ensures proper coordination between atrial and ventricular contractions.
Once the impulse reaches the ventricles, it travels through specialized conducting fibers called the Purkinje fibers, which conduct the impulse from the apex of the heart to the rest of the ventricular myocardium, causing the ventricles to contract.