Final answer:
The conduction system of the heart starts with the SA node initiating the action potential, which spreads across the atria and causes them to contract. The action potential then reaches the AV node, where it is delayed, allowing the atria to complete their contraction. From there, the action potential travels through the AV bundle and its branches to the Purkinje fibers in the ventricles, causing them to contract.
Step-by-step explanation:
The conduction system of the heart starts with the sinoatrial (SA) node, which is located in the right atrium. The SA node initiates the action potential, which spreads across the atria, causing them to contract. During this stage, the tricuspid and mitral valves are open, allowing blood to flow from the atria to the ventricles.
The action potential then reaches the atrioventricular (AV) node, where it is briefly delayed, allowing the atria to complete their contraction and empty their contents into the ventricles. At this stage, the tricuspid and mitral valves are still open, while the pulmonic and aortic valves are closed.
After the delay, the action potential travels through the atrioventricular (AV) bundle (also known as the bundle of His) and its branches to the Purkinje fibers in the ventricles. As the action potential spreads through the ventricles, causing them to contract, the tricuspid and mitral valves close to prevent blood from flowing back into the atria. Meanwhile, the pulmonic and aortic valves open to allow blood to be pumped out of the heart and into the lungs and rest of the body, respectively.