How do our hearts beat 24/7 without needing to take a break/rest period?
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They’re hyper-specialist cells for just this purpose. Cardiac muscle cells ditch all the storage space and reproductive parts and max out on mitochondria.
100% power all the time.
They don’t need to save fuel, they’re in the heart and have first dibs on fuel.
They don’t need to have regenerative capacity, you’re double dead if you take damage there anyway and they’re encased in a bone shield
They don’t need to worry about waste buildup – just dump it into the passing blood flow.
They don’t need to manage temperature changes, they’re deep in your core and well insulated.
All the things normal muscle cells have to worry about don’t matter, just max power all day every day.
The heart is made up of four chambers: the right atrium, the left atrium, the right ventricle, and the left ventricle. The atria are the upper chambers of the heart and the ventricles are the lower chambers. The right side of the heart pumps blood to the lungs to pick up oxygen. The left side of the heart pumps oxygen-rich blood to the rest of the body.
The heart is a muscle and like all muscles, it needs a constant supply of oxygen and nutrients to keep it healthy and functioning properly. The heart gets these things from the blood that flows through it. The heart also needs to get rid of waste products, such as carbon dioxide, that it produces.
The heart has its own electrical system that controls the rate at which it beats. This system is made up of four parts: the sinoatrial node (SA node), the atrioventricular node (AV node), the bundle of His, and the Purkinje fibers.
The SA node is a group of cells in the right atrium. The SA node is important because it sets the pace of the heart beat. The SA node sends out electrical signals that make the atria contract.
The AV node is a group of cells in the lower right chamber of the heart. The AV node is important because it delays the electrical signal before it goes to the ventricles. This delay gives the atria time to contract and fill the ventricles with blood.
The bundle of His is a bundle of fibers that goes from the AV node to the Purkinje fibers. The bundle of His carries the electrical signal to the ventricles.
The Purkinje fibers are a network of fibers in the ventricles. The Purkinje fibers carry the electrical signal to the muscles of the ventricles. This signal makes the ventricles contract and pump blood out to the body.
The heart beats about 60-80 times per minute when we are at rest. That means that the heart pumps about 2,000 gallons (7,570 liters) of blood every day!
It doesn’t.
All the individual muscle fibers are essentially resting for over 2/3 of the cycle.
There are rest periods built into every beat cycle.
The atrial beat (“top half”of the heart) pushes blood down into the ventricles (“bottom half”).
When that finishes, the ventricular beat begins – a few things are all happening at the same time here:
1- ventricles start squeezing – pushing blood out to the lungs and body
2- the valve flaps get pressed to close by the pressure build up created by this squeeze, preventing backward flow to the atria
3- the atrial muscles are resting, allowing those chambers to refill
4- A very slight atrial vacuum is created while the muscle wall elasticity pulls the atrial walls back to filled and ready to pump position
As the ventricular pumping finishes, those chambers begin their rest period.
Now, for a short time NO muscle contraction is happening – both chamber sets are resting, filling slightly by passive drainage. There is detectable electrical activity as ions are passing across membranes, preparing for the next beat cycle to begin.
Next beat cycle starts – atrial beat begins, ventricles are still resting – refer back to the Atrial beat above, and repeat indefinitely.
If your question is more HOW this keeps working without conscious control – then the answer is that the process is controlled by a self-exciting bundle of nerve fibers referred to as the SA (sino-atrial) node, which begins the beat cycle directly. The atrial signal then stimulates the rest of the non-self excitory electro-conducive mediation of the beat cycle.
The ELI5 explanation would be that it DOES rest more than it’s active
Added up in a day, it contracts(works) less than it rests
You can listen to your heart beat, it goes Du-du-breeak-Du-du-breeak
The heart does rest. In-between beats.
No rest would mean it’s in a state of permanent contraction, which it isn’t. It contracts, then rests, then contracts then rests, etc indefinitely.
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”
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.
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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.
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
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