How do our hearts beat 24/7 without needing to take a break/rest period?
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Got an echocardiogram yesterday and walked out pondering this exact question. Whoosh! Whoosh! Whoosh! Heart never gets a break.
They do rest, between every single beat, otherwise it would just be one long sustained contraction LOL
The heart is made of a different muscle configuration. The fibers arre smaller and tighter and far more interconnected than other muscles. This means that minor damage can be repaired and other fibers can simply bear the load and the muscle tears much less easily.
You can still overload a heart of course and obviously this is not recommended, but the key to your question is that heart muscles are simply configured differently and optimized for their role in a somewhat different way that sacrifices raw power for interconneced structures that allow minor damage to be easily repaired..
https://en.wikipedia.org/wiki/Cardiac_muscle
It’s because the heart is made of cardiomyocytes, not skeletal muscle.
In regular muscle, three things cause fatigue.
* Nerves get overstimulated making it harder for them to sustain a signal. So you need to push harder to make a muscle respond the same
* Muscles run out of fuel to meet the demands they need. Normally they taken in glucose to fuel oxidative phosphorylation and generate those muscle contractions. However, when a muscle is used too much, the ability of them to make energy from fuel is far lower than how much they need so they run out of fuel
* Muscles themselves get tired due to accumulation of things like lactic acid, impacting ability of Ca2+ and other critical components to work as well.
In cardiac muscle, these 3 things don’t really happen
* Cardiac muscle doesn’t have nerve innvervation. They rely on either themselves (cardiac muscle can beat themselves) or through their neighbors (which is how the wave of contractions in the heart occur).
* Muscles have more than 10x more energy production (mitochrondria), so doesn’t run out
* Cardiomyocytes can actually use lactic acid as well as other molecules as fuel to make energy, so those things are less likely to accumulate. If you overwork your muscle though, you can get acidosis but that occurs far after all your other muscles have tired out
They actually take a few milli seconds of mini break in between beats. It’s a really really short break, it’s like a smol tiny power nap.
They aren’t working balls to the wall all the time. The cells with a steady supply of sugar and oxygen will pump indefinitely at a normal rate. If something causes them to work super hard (increase rate, force, etc) for too long, or deplete their oxygen supply (heart attack, suffocation) it’ll shut down
Basically there are 3 types of muscle cells in your body.
The most basic is the ones that you think of when thinking “muscle”, these are called “Skeletal Muscle Cells”, these muscles can produce a very fast and strong contraction, but generally they can only act in a short period of time before they get “fatigued”. These are you voluntary muscles (at least most of them).
The second type of muscle is called “Smooth muscle cells”, these are located in your internal organs like your stomach and intestines. You are not able to control them, they usually are able to work without “fatiguing”, but have a low contraction power.
The third muscle cell type is your Cardiac Muscle cells, these are the muscles that make up your heart, and basically, they are the best of both muscle types. Not only are they adapt in working basically forever, but also have a fairly strong contraction potential.
Each cell type is built differently for different functions, but basically, it is the way the heart cells are built.
One primary reason they are able to resist fatigue is that they have much more mitochondria than other muscle cells and the structure of the proteins are different as well.
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It does rest every beat, not all of your heart contracts at the same time, it has a sequence.
Like in an engine, not all cylinders do tho work at the same time. Depending on the design only one or two cylinders have fuel exploding in it. Some of them just move with the momentum or pushing out waste.
The heart does take breaks, but it’s between each stroke.
The sounds you hear as heartbeat are not directly caused by the contraction, but by the closing and opening of the ventricles.
Even so, broken down onto seconds, the heart spends more time in rest mode than in systole-diastole, aka “beating”
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