Logan Steele
Cardiac muscle, also known as myocardium, is one of three types of muscle tissues found in the human body, the other two being skeletal and smooth muscle. It is an involuntary, striated muscle that forms the main tissue of the heart wall. The cardiac muscle is composed of individual cardiac muscle cells or cardiomyocytes, which are joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The primary function of the cardiac muscle is to contract and release involuntarily, keeping the heart pumping and blood circulating throughout the body.
| Characteristics | Values |
|---|---|
| Location | Forms the thick middle layer of the heart |
| Types | Myocardium, cardiomyocytes, pacemaker cells |
| Function | Keeps the heart pumping and relaxed |
| Contraction | Involuntary and rapid |
| Relaxation | Involuntary |
| Shape | Cylindrical |
| Size | 100μm long and 10–25μm in diameter |
| Cell structure | Tubular |
| Composition | Chains of myofibrils, sarcomeres, myofilaments, actin, myosin, calcium |
| Cell connections | Intercalated discs |
| Cell communication | Electrical impulses, excitation-contraction coupling |
| Cell nuclei | Single or double |
| Mitochondria | Present |
| Aerobic exercise | Can help keep the tissue strong and healthy |
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What You'll Learn
Cardiac muscle tissue is only in the heart
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle tissue, or myocardium, is a type of muscle tissue that forms the heart. It is the only organ that is also a muscle. It is made of a special type of muscle tissue called cardiac muscle, which does not exist anywhere else in the body.
Cardiac muscle tissue produces involuntary movements, meaning they are automatic and a person cannot control them. It contracts and releases involuntarily, keeping the heart pumping blood around the body. This is in contrast to skeletal muscle tissue, which is present in the arms and legs and moves voluntarily. Cardiac muscle tissue gets its strength and flexibility from its interconnected cardiac muscle cells, or fibres.
Cardiac muscle cells are the contracting cells that allow the heart to pump. Each cardiomyocyte needs to contract in coordination with its neighbouring cells. This is known as a functional syncytium. If this coordination breaks down, the heart may not pump at all, as can occur during abnormal heart rhythms such as ventricular fibrillation. The cells are surrounded by an extracellular matrix produced by supporting fibroblast cells.
Cardiac muscle contains cardiac muscle cells, which perform highly coordinated actions that keep the heart pumping and blood circulating throughout the body. The heart also contains specialised types of cardiac tissue containing "pacemaker" cells. These contract and expand in response to electrical impulses from the nervous system. Pacemaker cells generate electrical impulses, or action potentials, that tell cardiac muscle cells to contract and relax. The pacemaker cells control heart rate and determine how fast the heart pumps blood.
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It contracts and releases involuntarily
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Unlike skeletal muscle tissue, which is present in the arms and legs, cardiac muscle tissue produces involuntary movements. This means that they are automatic, and a person cannot control them. Cardiac muscle, also called myocardium, is a type of muscle tissue that forms the heart and exists only in the heart.
Cardiac muscle contracts and releases involuntarily, keeping the heart pumping blood around the body. The heart also contains specialized types of cardiac tissue containing "pacemaker" cells. These contract and expand in response to electrical impulses from the nervous system. Pacemaker cells generate electrical impulses, or action potentials, that tell cardiac muscle cells to contract and relax. The pacemaker cells control heart rate and determine how fast the heart pumps blood.
The individual cardiac muscle cell (cardiomyocyte) is a tubular structure composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. Thin myofilaments contain the protein actin, and thick myofilaments contain the protein myosin. The myofilaments slide past each other as the muscle contracts and relaxes. This process activates from the release of calcium from the sarcoplasmic reticulum (SR) when delivering an action potential to the muscle, in a process called excitation-contraction coupling. The sliding of actin and myosin past each other produces the formation of “cross-bridges,” which causes contraction of the heart and generation of force.
Cardiac muscle contraction occurs via the sliding filament model of contraction, much like skeletal muscle. Calcium is released from the sarcoplasmic reticulum (SR) in two ways: G-protein coupling facilitates the release of Ca2+ from the SR. This is particularly important in muscle types that require calcium-induced calcium release (e.g. in cardiac muscle). Ca2+ channels on the SR open and Ca2+ is released. Action is then terminated by IP3 phosphatase (IP3 is cleaved to IP2). Via Ryanodine receptors (RyR): These are a family of Ca2+-releasing channels found on intracellular organelles that store or release Ca2+. Membrane depolarization opens voltage-operated calcium channels (VOCCs) in the T-tubule system.
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It contains pacemaker cells
Cardiac muscle tissue, or myocardium, is a type of muscle tissue that forms the heart. It is one of three types of muscle in the body, the other two being skeletal and smooth muscle. The myocardium is surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium.
Cardiac muscle tissue exists only in the heart, where it is responsible for keeping the heart pumping and relaxing normally. It contracts and releases involuntarily, keeping the heart pumping blood around the body.
Cardiac muscle contains many types of cells, including fibroblasts, smooth muscle cells, and cardiomyocytes. It also contains specialised types of cardiac tissue that contain pacemaker cells. These contract and expand in response to electrical impulses from the nervous system. Pacemaker cells generate electrical impulses, or action potentials, that tell cardiac muscle cells to contract and relax. The pacemaker cells control heart rate and determine how fast the heart pumps blood.
Pacemaker cells are self-excitable and able to depolarize to threshold and fire action potentials on their own. This is known as autorhythmicity. They do this at set intervals, which determine heart rate. Because they are connected with gap junctions to surrounding muscle fibres, the specialised fibres of the heart's conduction system, the pacemaker cells are able to transfer the depolarization to the other cardiac muscle fibres in a manner that allows the heart to contract in a coordinated manner.
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It can be affected by cardiomyopathy
Cardiac muscle tissue, or myocardium, is a type of muscle tissue that forms the heart. It is responsible for keeping the heart pumping and relaxing normally. It contracts and releases involuntarily, which keeps the heart pumping blood around the body.
Cardiomyopathy refers to conditions that affect the heart muscle. It can cause the heart to lose its ability to pump blood efficiently, leading to fatigue, shortness of breath, or heart palpitations. Cardiomyopathy can make the heart stiffen, enlarge, or thicken, and it can also cause scar tissue. There are several types of cardiomyopathy, including dilated cardiomyopathy, hypertrophic cardiomyopathy (HCM), and restrictive cardiomyopathy (RCM).
Dilated cardiomyopathy causes the cardiac muscle tissue of the left ventricle to stretch and the heart's chambers to dilate. This can lead to the heart's inability to pump blood effectively. HCM is a genetic condition in which the cardiomyocytes do not have a typical formation. It can interrupt blood flow out of the ventricles, cause arrhythmias, or lead to congestive heart failure. RCM occurs when the walls of the ventricles become stiff, preventing the ventricles from filling with enough blood and reducing the heart's ability to pump blood.
Cardiomyopathy can also be caused by other diseases or their treatments, such as complex congenital heart disease, nutritional deficiencies, fast heart rhythms, or certain types of chemotherapy. In some cases, the exact cause of cardiomyopathy is unknown. While there is no cure for cardiomyopathy, treatments are available to help manage symptoms and slow down the disease's progression. Lifestyle changes, such as a healthy diet, regular exercise, and stress reduction, can also help strengthen the heart and improve overall health.
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It can be damaged by myocarditis
Cardiac muscle, also known as myocardium or heart muscle, is a type of muscle tissue that forms the heart. It is one of three types of muscle tissues found in vertebrates, the others being skeletal and smooth muscle. Cardiac muscle is only found in the heart and is responsible for keeping the heart pumping and blood circulating around the body. It contracts and releases involuntarily, and its rhythmic contractions are regulated by the sinoatrial node of the heart, which serves as the heart's pacemaker.
Cardiac muscle can be damaged by myocarditis, an inflammation of the heart muscle. Myocarditis can develop suddenly (acutely), be recurring, or be long-lasting (chronic). It is often caused by viral infections or inflammatory conditions, and symptoms can start to show one to two weeks after being unwell with an infection. Common symptoms include chest pain or discomfort, shortness of breath, and flu-like symptoms such as high temperature, headaches, body aches, and joint pain. In rare cases, if the inflammation is severe, myocarditis can scar the heart muscle, making it bigger and weaker over time. It can also affect the heart's electrical system, leading to an irregular heartbeat (arrhythmia).
The treatment for myocarditis depends on the severity of the symptoms and the extent of inflammation. Mild cases may resolve on their own, while more severe cases may require medication or even surgery. Many people can live for years without problems after receiving treatment, but there is a small risk of recurrence. Myocarditis can sometimes lead to serious complications, such as dilated cardiomyopathy, where the heart becomes enlarged and weak, and it has been linked to nearly 20% of sudden deaths in young people.
It is important to seek medical attention if you are experiencing any symptoms of myocarditis. Early diagnosis and treatment can help lower the risk of long-term complications. While it is difficult to avoid all the causes of myocarditis, maintaining good hygiene, getting vaccinated, and limiting alcohol intake and prohibited drug use can help reduce the risk of developing the condition.
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Frequently asked questions
Cardiac muscle tissue is located in the heart and is responsible for its pumping action.
The primary function of cardiac muscle tissue is to contract and relax involuntarily, keeping the heart pumping blood around the body.
Unlike skeletal muscle tissue, which is controlled voluntarily, cardiac muscle tissue contracts and relaxes automatically without conscious input. It is also highly organised, containing various cell types and unique features that allow it to contract in a coordinated manner.
No, cardiac muscle tissue is unique to the heart and is not found elsewhere in the human body.
