Anatomy Physiology

The human heart is one of the most fascinating structures in the body. Your heart beats every second of every day of your life, without rest (you hope) and without pause. The heart is made mostly of very specialized muscle. The muscle cells of the heart are of a type that are not found anywhere else in the body. They are called cardiac myocytes by scientists and doctors. This article will serve as an introduction to human cardiac muscles.

There are three major types of muscles in the human body. They are smooth, striated, and cardiac muscles. Cardiac muscles have several distinct features that make them unique. The are an involuntary muscle (as are smooth muscles). This means that you don’t have to think about contracting them – this is convenient as it would be a real distraction to always have to be thinking about making your heart beat.

The contraction of cardiac muscles is a highly coordinated event. The cells must contract in a very specific sequence in order to make the heart serve as a pump. There is an area of the heart on the right atria where the electrical signal to contract begins. This is known as the sinus node. The cardiac cells in the sinus node automatically contract. They then send an electrical signal around the rest of the heart. There are many diseases related to the cardiac myocytes not beating in the right order, or receiving mixed or incomplete contraction signals.

Cardiac muscle cells that make up the walls of the heart do not actually use the blood in the heart to get their nourishment. This is somewhat unusual – they are entirely bathed in blood, but cannot use that blood for energy. Instead, there are a series of arteries, the coronary arteries, that feed the cells of the heart muscles. Blockages in these arteries can cause a heart attack, despite the fact that the heart still has lots of blood flowing through the four chambers. Not a very efficient system, but it’s what we’ve got.

Cardiac myocytes do not tire easily. In fact, they hardly ever tire, and they certainly never need to stop completely. All cardiac muscle cells have a very high number of mitochondria. Mitochondria are the mall intracellular structures that are responsible for making energy that the cells use to contract. 

The muscle cells of the heart require a large amount of oyxgen to function. They get virtually none of their energy from anaerobic metabolic functions. Everything they do requires oxygen. This is why things go very badly for someone when the coronary arteries become blocked. No flow through the coronary arteries means no oxygen, which means no pumping. 

There are specialized structures, known as intercalated disks, that are responsible for propagating the electrical signals throughout the heart. These structures are unique to the cardiac muscle cells. They connect the heart muscles and allow the signal to contract to spread around the heart in a very specific pattern.

In addition to oxygen, human heart muscles require a variety of other chemicals in order to function properly. They need a good amount of calcium, potassium, and sodium. Too much or too little of any of these electrolytes can cause the heart muscles to malfunction. Of course, your body does a pretty good job regulating the levels of these chemicals automatically. Some diseases and medical conditions can however stem from imbalances in these chemicals.

So there you are, an introduction to human cardiac muscles. Of course, there is a lot more than could be learned about these unique and fascinating structures. In fact, entire textbooks have been written on how they function.