Dominic Stone
The cardiac muscle, also known as myocardium, is a type of muscle tissue that forms the heart. It is one of three types of muscle tissues in the body, the others being skeletal and smooth muscle. The cardiac muscle is involuntary and makes up the thick middle layer of the heart, with blood supplied by the coronary arteries. It contracts and relaxes to pump blood through the circulatory system, and its unique structure allows it to contract in a coordinated fashion. Regular aerobic exercise can help strengthen the cardiac muscle and keep the heart healthy.
| Characteristics | Values |
|---|---|
| Type | Cardiac muscle tissue is one of the three types of muscle tissues in the body, the others being skeletal muscle and smooth muscle |
| Location | Cardiac muscle tissue is only found in the heart |
| Function | Cardiac muscle tissue contracts and releases involuntarily to keep the heart pumping blood around the body |
| Composition | Cardiac muscle tissue is composed of individual cardiac muscle cells or cardiomyocytes joined by intercalated discs |
| Structure | Cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium) |
| Blood supply | Blood is supplied to the cardiac muscle by the coronary arteries and drained by the cardiac veins |
| Strengthening exercises | Regular aerobic exercise can help strengthen the cardiac muscle tissue and keep the heart and lungs healthy |
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What You'll Learn
Cardiac muscle cells
The rate and force of cardiac muscle cell contraction are critical in determining the normal pumping performance of the heart. The contraction of individual cardiac muscle cells produces force and shortening in the bands of muscle, with a resultant decrease in the heart chamber size and the consequent ejection of blood into the pulmonary and systemic vessels. The contraction of cardiac muscle requires a constant supply of oxygen and nutrients, which is provided by the coronary arteries.
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Contraction and relaxation
Cardiac muscle tissue, also called myocardium, is a type of muscle tissue that forms the heart. It is one of three types of muscle tissue 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 contracts and relaxes involuntarily, keeping the heart pumping blood around the body. 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.
The contraction of individual cardiac muscle cells produces force and shortening in these bands of muscle, with a resultant decrease in the heart chamber size and the consequent ejection of blood into the pulmonary and systemic vessels. The myofilaments slide past each other as the muscle contracts and relaxes. This process is activated by 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.
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.
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Blood supply
The cardiac muscle, also called the myocardium, is a type of muscle tissue that forms the heart. It is one of the three types of muscle tissues in the body, the other two being skeletal and smooth muscle tissues. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) or epicardium and the inner layer (the endocardium).
The cardiac muscle receives blood supply via the coronary circulation. The coronary arteries supply blood to the myocardium, and the cardiac veins drain this blood. The coronary arteries are the first branches of the aortic root. There are left and right coronary arteries. The right coronary artery (RCA) supplies the right ventricle and the bundle of His. In 85% of people, it gives a branch known as the posterior descending artery (PDA), which supplies the AV node, posteromedial papillary muscle, and posterior portion of the interventricular septum and the ventricles. The left main coronary artery branches off to give the left circumflex coronary artery (LCX) and the left anterior descending artery (LAD).
The process of contraction and relaxation of the cardiac muscle requires a constant supply of oxygen and nutrients to meet its energy demands. Ischemic syndromes, such as angina pectoris, acute myocardial infarction, and sudden cardiac death, occur when there is a diminished blood supply to the heart tissue. This can be due to coronary artery atherosclerosis, where an atherosclerotic plaque obstructs the lumen of a major epicardial artery.
To maintain a healthy cardiac muscle, regular aerobic exercise is recommended. Cardio workouts help lower blood pressure, reduce heart rate, and improve the efficiency of the heart pump. Common types of cardio exercises include walking, running, biking, and swimming. Additionally, maintaining a heart-healthy diet, quitting smoking, and controlling cholesterol and blood pressure are crucial for cardiovascular health.
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Intercalated discs
Cardiac muscle tissue, or myocardium, is a type of muscle tissue that forms the heart. It is one of three types of muscle tissues 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. Coronary arteries supply blood to the cardiac muscle, and cardiac veins drain it. Cardiomyocytes are the individual cells that make up the cardiac muscle, and they contract involuntarily to generate the pressure needed to pump blood through the circulatory system.
Cardiac muscle tissue works to keep the heart pumping through involuntary movements, which is one feature that differentiates it from skeletal muscle tissue, which is present in the arms and legs and can be controlled. This is achieved through specialized cells called pacemaker cells, which control the contractions of the heart. The nervous system sends signals to the pacemaker cells, prompting them to either speed up or slow down the heart rate. These pacemaker cells are connected to other cardiac muscle cells, allowing them to pass along signals and resulting in a wave of contractions that create the heartbeat.
The intercalated disc was first described in detail in 1966 using electron microscopy, which revealed its complex nanostructure. It has since been recognized as a highly specialized structure that connects cardiomyocytes via mechanical and electrical junctions. The intercalated disc is not just the sum of its individual molecular components but an interacting molecular complex where components work together to bring about electrical and mechanical synchrony.
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Pacemaker cells
The cardiac muscle, or myocardium, is a type of muscle tissue that forms the heart. It is one of three types of muscle tissues 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 works to keep the heart pumping through involuntary movements, which is one feature that differentiates it from skeletal muscle tissue, which is present in the arms and legs and can be controlled. This is achieved through specialised cells called pacemaker cells. These cells control the contractions of the heart. The nervous system sends signals to pacemaker cells that prompt them to either speed up or slow down the heart rate.
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Frequently asked questions
Cardiac muscle, also called heart muscle or myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart.
Cardiac muscle contracts in a similar manner to skeletal muscle, although with some important differences. Electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. This release of calcium activates the contractile proteins of the cell.
The release of calcium from the sarcoplasmic reticulum causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. This process allows the cardiac muscle to contract in a coordinated fashion and resist fatigue.
