How does my heart know to keep beating?

You asked: How does my heart know to keep beating?

Just like how people ask why the sky is blue and then there’s finally someone who knows about light refraction, the reason the heart knows to keep beating is not “just cuz.”

The basics

For those who are unfamiliar with how the heart works in general, it’s all boils down to plumbing, pumping, and electricity. The correct plumbing ensures that the blood flowing through the heart goes in the right direction by using a series of valves that separate the heart’s 4 entry and exit points into/out of the chambers. The pumping function is what allows blood to actually flow out of the heart and either toward the lungs to pick up oxygen or the body to deliver that oxygen to the tissues. The electricity is the brains behind the operation.

Pump, Plumbing, and Electricity

There are specialized regions of the heart that are more electrically active and allow the muscle to have coordinated activity resulting in effective pumping and flow. In other words, changes in the ion concentrations of sodium, potassium, and calcium inside and outside of the cells result in the individual muscle cells contracting. When one cell contracts, it passes that signal along to its neighboring cells through special ion channels that result in more cells contracting… and more… and so on. In other words, the heart’s electrical system is what tells the heart muscle to contract and when. Normally, this all starts in the part of the heart called the sinoatrial node (“SA node”).

Can’t get enough? (Warning: Physics is coming!)

Heart and Conduction System

For physics geeks out there, all parts of the heart have what’s called an intrinsic depolarization rate. Basically, this means that even while the heart muscle is resting in between beats, ions like sodium, potassium, and calcium are constantly in flux either going into or out of cells. Since all of those ions carry an electrical charge with them, their movement results in a charge build-up, which ultimately reaches a point of no return, called the threshold. Once the cells reach that point, there’s no going back. After reaching the threshold, the cell depolarizes – or allows ions to rush in – ultimately resulting in muscle contraction.

After the ions rush in and the muscle contracts, other itty-bitty ion pumps will put all those ions back where they came from and the whole process starts all over again.

Still with us?

This whole process repeats about 100,000 times each day. Since all the cells in the heart are just “taking orders,” so-to-speak, from their neighboring cells, the cells of the heart that let the most ions leak in while at rest (not beating) get to decide how fast the heart beats. Various things, including your nervous system’s fight-or-flight (sympathetic) or rest-and-digest (parasympathetic) response play into how quickly those cells with go through this cycle of contracting and relaxing, resulting in your heart rate.

Arrhythmias, or abnormal heart rhythms, often result from parts of the heart outside of the SA node going off before the SA node does. Since all the cells are just listening to their neighbors to know when to beat, the fastest cell wins whether it’s the SA node or not.

Fear not… I have great news for you! All of this happens without you needing to think about it. If you do decide to think about it though, thank your heart and treat it well!

 

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