Final answer:
The heart is told to beat by electrical impulses sent and received by the sinoatrial (SA) node and atrioventricular (AV) node. The Purkinje fibers carry the electrical signals to cause ventricular contraction.
Step-by-step explanation:
The heart is told to beat by electrical impulses. These impulses are sent and received by an upper "fuse box" called the sinoatrial (SA) node, and a lower "fuse box" called the atrioventricular (AV) node. The "wires" that carry the electricity break off into two bundle branches and are called Purkinje fibers.
The electrical signals start at the SA node, causing the atria to contract. Then, the signal reaches the AV node, where it pauses before spreading to the ventricles. From the AV node, the signal enters the bundle of His, then the left and
right bundle branches, and finally the Purkinje fibers that conduct the impulse to cause ventricular contraction.
This electrical conduction system allows the atria to empty completely into the ventricles before the ventricles pump out the blood, ensuring efficient heart function.