Which type of cells are responsible for the spontaneous generation and conduction of electrical impulses in the heart?

Pacer cells, also known as pacemaker cells, are specialized cells in the heart that have the unique ability to generate and conduct electrical impulses spontaneously. These cells are primarily located in the sinoatrial (SA) node, which is often referred to as the heart's natural pacemaker. The spontaneous activity of pacer cells is crucial for initiating the cardiac cycle and maintaining a regular heart rhythm.

Unlike muscle cells (which contract in response to electrical signals), endothelial cells (which line blood vessels), and myocardial cells (the main muscle cells responsible for the heart’s contractions), pacer cells play a distinct role in the electrical conduction system of the heart. They generate action potentials that propagate through the heart's conduction system, leading to synchronized contractions of the atria and ventricles. This process is essential for effective pumping of blood throughout the body.

In summary, pacer cells are essential for the intrinsic regulation of heart rate and rhythm, making them the correct choice in this context.