The Electrical System of the heart

I think it is helpful to compare the human heart with the automobile engine.  To work properly the auto must have 3 components:  An engine to power the car, an electrical system that includes a generator of electrical current and a wiring system to carry the current to every cylinder (spark plug wires), and an energy source, gasoline.   Similarly with the heart, the left ventricle is the engine and it powers the heart and circulates the oxygenated blood, the gasoline or energy source for the body,  The heart also has a generator of electrical current, called a pacemaker,  that generates an electrical impulse.  This electrical current  is distributed to all the heart muscle via a wiring system composed of specialized muscle cells to stimulate a heart contraction.  All 3 components must be working properly to have a smooth running car as well a smooth running heart.  This all happens in a fraction of a second.  If anything goes wrong with any one of these 3 components, symptoms develop.  Without a generator the car will not start nor move even though the engine is in excellent shape and the tank is filled with gas.  The same is true of the heart.  Without a pacemaker we don’t go anywhere, illustrating the importance of a normally functioning pacemaker in preserving and maintaining life.

Pictured here is a cut-away picture of the 4 chambered heart with a schematic diagram of the electrical system.  The generator of the electrical impulse that drives the heart is called the “Sinus Node or SA Node” and it is located in the right upper corner of the right atrium.  The SA node is composed of specialized cells that spontaneously depolarize (ignite) and generate an electrical impulse.  Isn’t that amazing that human cells can generate the electrical impulse all by themselves?  The impulse then spreads through the heart from the SA Node to the lower chambers, stimulating heart muscle to contract as it travels this course.  Think of this:  Our heart will beat in the neighborhood of 100,000 times per day, year in and year out, which means it is an extremely stable and reliable system, functioning normally under all types of human conditions.  The SA node can speed up with exercise and/or slow down depending on body requirements for blood flow, showing the versatility of the system. (to be continued)