Why doesn't your heart get cramp

MooseJam

Any other muscle gets tired out and cramps if you use it too much - how does your heart beat continuously without ever tiring or cramping ?

jessconr

when someone has a heart attack this usually means the heart is cramping

Killgore Trout

MooseJam wrote: »

Any other muscle gets tired out and cramps if you use it too much - how does your heart beat continuously without ever tiring or cramping ?

http://en.wikipedia.org/wiki/Cardiac_muscle

celestial

MooseJam wrote: »

Any other muscle gets tired out and cramps if you use it too much - how does your heart beat continuously without ever tiring or cramping ?

I believe it can 'cramp' - check out myocardial infarction/aka heart attack!! I imagine palpitations fall under that bracket too.

aye

muscle which get cramps and tire are skeletal muscles, your heart is different type of muscle, cardiac muscle.

skeletal muscle is made up of muscle fibers, subsequently made up of myofibrils.
when lifting weights/working out, its the myofibrils in the skeletal muscle that "tear", leading to DOMS.

the cardiac muscle is not the same design as the skeletal muscle. in the cardiac muscle the myofibrils are branched. these branches interlock with the branches of adjacent fibers making stong junctions. these junctions enable the heart to contract forcefully without tearing.

good explanation here
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Muscles.html

bwardrop

Aye is correct in what he says - to expand it a little and clear up some confusion, I add the following.

A cramp is an involuntary tetanic contraction of the skeletal muscle. This means that the signals that stimulate your muscles to contract are fired off so quickly that they become almost continuous and the muscle 'cramps' - it is a sustained contraction. During a cramp, the 'contraction signals' are fired off at a much greater rate than you can generate voluntarily. There are a couple of theories re: cause, but nothing definitive yet.

A myocardial infarction (heart attack) is caused by a sudden insufficiency in the blood supply a specific area of the heart muscle. It is usually caused a blockage of one of the coronary arteries (artery that supplies blood from the heart to the heart).

The heartbeat may be disrupted in many ways - these are known as arrhythmias. A few common ones are bradycardia (slow heart beat) and tachycardia (fast heart beat). Ventricular fibrillation is when the signals that stimulate the heart to beat become totally uncoordinated and the heart becomes unable to pump blood. This is a fatal condition, unless someone trained in CPR and defibrillator are immediately available. I think this is what is being confused in this thread as a "cramp" of the heart muscle.

A cramp in skeletal muscle and ventricular fibrillation of the cardiac muscle are both caused by abnormalities in the signal pattern which causes contraction, but are not the same thing.