Select the correct route through which the pulse-making impulse travels in the heart.

SA node$\to$AV node$\to$Bundle of His$\to$Purkinje fibres$\to$Heart muscles.

• SA Node (Sinoatrial node): The SA node is often referred to as the natural pacemaker of the heart. It initiates electrical impulses, and when it fires, it generates an action potential about 60-100 times per minute in a healthy adult. These electrical signals spread across the atria, causing them to contract and push blood into the ventricles.
• AV Node (Atrioventricular node): The electrical impulses generated by the SA node travel to the AV node, which is located in the atrial septum. The AV node briefly delays the impulses to allow the atria to fully contract before transmitting the signals to the ventricles.
• Bundle of His: After the AV node, the electrical signals travel through the Bundle of His, which is a collection of specialised fibers that pass through the interventricular septum, separating the left and right ventricles.
• Purkinje Fibers: The Bundle of His divides into smaller branches known as Purkinje fibers. These fibres rapidly transmit the electrical impulses down the ventricles, causing them to contract in a coordinated manner.
• Heart Muscles: The Purkinje fibers deliver the electrical signals to the muscle cells of the ventricles, causing them to contract from the bottom (apex) upward, forcing blood out of the heart into the circulatory system.