HOW THE CONDUCTION SYSTEM CONTROLS HEART RATE

In the conduction system, the flow of current in a cell is passed on to adjacent cells. In the heart muscle cells, the same thing happens, but in addition the electrical current activates the contractile apparatus of the cell. When the contractile apparatus is activated, it initiates the action of the heart muscle. Thus, the conduction system, from the sinus node on down, is responsible trolling the speed and rhythm of your heart's contraction.

Unlike most other muscle the body, cardiac cells can initiate their own electrical impulse contraction. Although the nervous system can adjust the rate at which the heart beats, it is not the driving force that makes it beat. Even a heart that has been removed from the body, or cardiac cells that have been separated from one another, can continue to contract for a while. In fact, even if the sinus node fails, other sites can take over the pacemaking function.

The reason that the sinus node sets the pace is that its natural rate for formation of the electrical impulse is faster than the rates in other cells farther down in the conduction system, and the faster rate overrides the slower the rates. As you go down the conduction system, the rate of spontaneous contraction gets slower and slower. For example, in an adult the usual sinus node rate at rest is 60 to 100 beats per minute. The spontaneous rate AV node is 40 to 60 beats per minute and the rate in the ventricles is only 20 to 40 beats per minute.

Although the slower rate of impulse formation from an AV node site will keep you alive, your heart performs better under the direction of the node. Likewise, if neither the node nor the AV node is working, another backup system (in the ventricles) takes over. However, it is even s and is not designed to do the job alone.

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Cardio & Blood