https://www.reddit.com/r/explainlikeimfive/comments/2xbih3/eli5why_the_heart_doesnt_get_cramp/
created by LePhasme on 27/02/2015 at 04:40 UTC
7 upvotes, 6 top-level comments (showing 6)
If we exercise for a long time we get cramp in the muscles used, so why our heart which is a muscle that "never" stop working doesn't get a cramp ?
Comment by destroyingtocreate at 27/02/2015 at 09:20 UTC*
6 upvotes, 0 direct replies
There are 3 types of muscle in the body. Skeletal, smooth, and cardiac.
Smooth muscles are muscles that are found in the digestive system to create peristalsis - or the movement of food/nutrition through the digestive system. Smooth muscles are also in the female reproductive system.
Cardiac muscles = the heart/heart cells and control heart rate/function.
Smooth and cardiac are working without conscious thought, and these group of muscles are constantly working to maintain homeostasis/normal function. Skeletal muscles are voluntary, meaning a person has control over them.
So, because they are different types of muscle/cells (made up differently), they act differently and therefore, react differently to different situations, such as stress/fatigue.
Cardiomyocytes have a high mitochondrial density, which allows them to produce adenosine triphosphate (ATP) quickly, making them highly resistant to fatigue.
The Sinoatrial Node (or SA node which is located in the right atrium of the heart) is the hearts dominate pacemaker. The generation of pacemaking (or normal, regular heart rate/rhythm, which is 60-100 beats per min) is known as "automaticity." If the SA node fails (failure of the SA node would imply abnormal rhythms, a heart attack, a block, etc. - so you can think of this as the **cramp**) your heart's backup generator would then would kick in - the atrioventricular node (AV node, located between the atra and ventricles) would begin to take over the hearts pumping action. The AV node has a slower heart rate capacity and produces around 40-60 beats/min.
THEN - even if your SA and AV Nodes should fail, you are still left with a 3rd back up system - the Purkinje Fibers (or Bundle of His) which can sustain a beat of about 20-30, which is not really enough to help for long - and therefor at this point, you will need a different source (medical device/implant) to help pace your heart.
Hope this helps.
EDIT: Another relevant point (perhaps even more relevant than all the other afore mentioned stuff), is that people who become deficient or overly "intoxicated" with certain electrolytes (such as Potassium, Magnesium, and Calcium) are prone to cramps and spasms. And for someone who is unable to correct this (say, someone who has kidney failure and isn't filtering these products properly, which causes them to build up, or someone who has had their thyroid removed) it can begin to mess with the heart.
Comment by SpanishStallion at 27/02/2015 at 05:19 UTC
6 upvotes, 0 direct replies
I can take a stab at this. From my understanding, the heart's preferred energy source are fatty acids. Two main reasons, provide the most calories per gram as well as allow for continuous oxidative metabolism. That is, the heart will not use anaerobic metabolism to regenerate the high energy intermediates needed to convert food to basic cellular energy, that is ATP. This will decrease lactic acid build up and thus reduce cramping.
Comment by StupidLemonEater at 27/02/2015 at 05:04 UTC
1 upvotes, 0 direct replies
If your heart cramped up, you would die. It stands to reason that human evolution would keep that sort of thing from happening.
Comment by davidcarpenter122333 at 28/02/2015 at 06:01 UTC
1 upvotes, 0 direct replies
Because if it did, you would die, which means that there is quite a lot of evolutionary pressure to have a heart that doesn't cramp, and therefor ours evolved not to a long time ago.
Comment by [deleted] at 27/02/2015 at 07:23 UTC
-2 upvotes, 1 direct replies
Your heart can cramp up. Think about it, what happens when you get a cramp in, say, your leg? It seizes. What's another word for seize? Arrest. What's another word for the system your heart is in? Cardiac.
Your heart can cramp. You usually die as a result.
Comment by ForestNympho at 27/02/2015 at 05:04 UTC
-4 upvotes, 0 direct replies
If you get always cramps after exercising, you need to warm up and stretch more bud. Or exercise more in the first place.