Final answer:
The sinoatrial node is responsible for sending out electrical impulses that initiate depolarization, leading to heart muscle contraction and efficient blood pumping.
Step-by-step explanation:
The sinoatrial (SA) node sends out electrical impulses to initiate depolarization. Depolarization waves begin in the right atrium, instigated by the SA node, which acts as the heart's natural pacemaker. This wave of depolarization then travels across the superior portions of both atria and down through the contractile cells, allowing for the coordinated contraction of the heart muscles, necessary for efficiently pumping blood through the circulatory system.
An electrocardiogram can illustrate this process by showing the depolarization waves as they move across the heart. Electrical impulses trigger the opening of Na+ channels, causing Na+ to enter the cell, which depolarizes the membrane and initiates a series of events leading to muscular contraction.