How does the heart beat non-stop our entire lives?

By Casey Frye, CCNN Writer

heartbeat running
Our hearts beat non-stop whether we’re actively exercising or snoozing away.

Your heart is busy beating away whether you’re walking, running, sitting, standing, or sleeping; as long as you’re alive, that tough muscle in your chest is working non-stop… but  how can our hearts beat for an entire lifetime without rest?

It all has to do with special structures inside of our cells known as mitochondria. These tiny units are responsible for producing energy that our muscles and cells need to carry out their functions. The more mitochondria there are in a certain area, the more energy there will be to gobble up. However, the amount of mitochondria a muscle has depends on whether it’s one of three different types: skeletal, smooth, or cardiac muscle.

Skeletal muscle is connected to our bones and tendons, and they are completely “voluntary”, meaning they’re controlled at will. Whenever you kick a ball or write on paper, for example, they are hard at work. About 1-2% of a skeletal muscle’s weight is made up of mitochondria, and they produce enough energy to keep us moving all day. However, if we use up energy faster than it’s being produced, our muscles begin to tire out.

On the other hand, smooth muscles are smooth as the name implies. They can be found inside the lining of various organs like the small intestine (which extracts nutrients from the food you eat), blood vessels, and the stomach. They are completely “involuntary”, meaning they cannot be controlled at will. Instead, the brain is responsible for ensuring they carry out their functions. For example, you don’t have to think about digesting food. Similarly, you can’t prevent your stomach from growling loudly in class!

Finally, the cardiac muscle is found exclusively in the heart. The cells that make up the muscle are wound up really tight together so they can generate powerful force without tearing. Remember how about 2% of skeletal muscle volume was made up mitochondria? Well, cardiac muscles contain more than several times that amount. To be specific, they contain anywhere from 30-35% mitochondria by volume! This is enough to keep a steady and constant supply of energy during the toughest of workouts, and plenty to keep it at a rhythmic pulse while sleeping. In fact, it’s enough to last a lifetime.

Image of puddle runner courtesy of The World According To Marty on Flickr.