Final answer:
The statement is true; the sinoatrial node initiates an electrical signal that causes the atria to contract during systole, which is the heart's way of pumping blood.
Step-by-step explanation:
The statement that the sinoatrial node fires electrical signals, which then spread throughout the atrias causing them to depolarize and contract (systole), is True. The SA node, located in the right atrium, has the highest inherent rate of depolarization and is referred to as the heart's natural pacemaker. The electrical signals generated by the SA node cause the atria to contract, a phase known as atrial systole. After the atria contract, the signal reaches the atrioventricular (AV) node, where there is a slight delay that allows the atria to complete their contraction and pump blood into the ventricles. Following this, the impulse travels through the AV bundle, the bundle branches, and the Purkinje fibers, leading to ventricular contraction.