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Cardiac muscle, also known as myocardium, is the thickest section of the heart wall. It is one of three types of muscle tissues in the body, the other two being skeletal and smooth muscle. The myocardium forms a thick middle layer of the heart wall, sandwiched between the outer layer (epicardium or visceral pericardium) and the inner layer (endocardium). The thickness of the myocardium determines the strength of the heart's ability to pump blood, with the myocardium in the ventricles being thicker to allow for forceful contractions, while the myocardium in the atria is much thinner as these chambers fill through passive blood flow. The individual cardiac muscle cells, or cardiomyocytes, are responsible for the heart's contractions and have a distinctive striated or striped appearance due to the alternating thick and thin filaments of myosin and actin proteins.
| Characteristics | Values |
|---|---|
| Type of muscle tissue | Cardiac muscle tissue, or myocardium, is one of the three types of muscle tissues in the human body, the others being skeletal and smooth muscle. |
| Location | Cardiac muscle tissue exists only in the heart. |
| Function | Cardiac muscle tissue is responsible for keeping the heart pumping and relaxing normally. |
| Structure | Cardiac muscle is highly organized and bears similarities to skeletal muscle in terms of its basic morphology and function. It is composed of individual muscle fibres, which contain numerous, alternating thick and thin contractile filaments, which give each cell type its distinctive striated appearance. |
| Thickness | The myocardium is the thickest section of the heart wall, with its thickness varying in different parts of the heart. The myocardium of the left ventricle is the thickest, as this ventricle is responsible for generating the power needed to pump oxygenated blood from the heart to the rest of the body. |
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What You'll Learn
- Cardiac muscle is the thickest section of the heart wall
- The thickness of the myocardium determines the strength of the heart's ability to pump blood
- The left ventricle myocardium is the thickest part of the heart
- Cardiomyocytes are the individual cells that make up the cardiac muscle
- The thickness of the myocardium may change in some individuals as a response to disease
Cardiac muscle is the thickest section of the heart wall
The heart wall is made up of three layers, each with its own function: the outer epicardium, the middle myocardium, and the inner endocardium. The myocardium, or cardiac muscle, is the thickest section of the heart wall. It is composed of cardiac muscle fibres that contract and release involuntarily, keeping the heart pumping blood around the body.
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). It is made up of individual cardiac muscle cells or cardiomyocytes, joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The thickness of the myocardium determines the strength of the heart's ability to pump blood. The left ventricle myocardium is the thickest, as this chamber must create substantial pressure to pump blood into the aorta and throughout systemic circulation.
The individual cardiac muscle cell 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 organise into thick and thin filaments, called myofilaments. The thick filaments are composed of the protein myosin, and the thin filaments are composed of the proteins actin, troponin, and tropomyosin. The myofilaments slide past each other as the muscle contracts and relaxes, causing the cell to become shorter and fatter.
The cardiac muscle is highly organised and bears similarities to skeletal muscle in terms of its basic morphology and function. For instance, both types of muscle are composed of individual muscle fibres, which contain numerous, alternating thick and thin contractile filaments, which give each cell type its distinctive striated appearance. However, despite their many similarities, there are important differences between skeletal and cardiac muscle, which makes each uniquely suited to perform its designed function.
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The thickness of the myocardium determines the strength of the heart's ability to pump blood
The heart is made up of three layers of tissue, with the myocardium forming the thickest middle layer. The myocardium is composed of cardiac muscle fibres, which enable the heart to contract. The thickness of the myocardium varies in different parts of the heart, with the left ventricle being the thickest. This is because the left ventricle is responsible for generating the power needed to pump oxygenated blood from the heart to the rest of the body.
The myocardium contains cardiomyocytes, which are the contractile cells of the heart. These cells are shorter than skeletal myocytes and have fewer nuclei. Each muscle fibre connects to the plasma membrane (sarcolemma) with distinctive tubules (T-tubules). The T-tubules have a large number of calcium channels, which allow for a rapid exchange of calcium ions. This exchange stimulates an action potential, causing the cells to contract.
The coordinated contraction of cardiomyocytes causes the heart to contract and expel blood into circulation. Chambers of the heart with a thicker myocardium are able to pump blood with more pressure and force compared to chambers with a thinner myocardium. The myocardium is thinnest within the atria, as these chambers primarily fill through passive blood flow. The right ventricle myocardium is thicker than the atrial myocardium, as this muscle must pump all blood returning to the heart into the lungs for oxygenation.
The thickness of the myocardium may change over time and can adapt to compensate for diseases, often resulting in heart failure. For example, in cardiac hypertrophy, the walls of the heart become too thick to pump blood effectively. Cardiomyocyte hypertrophy occurs through sarcomerogenesis, the creation of new sarcomere units in the cell. During heart volume overload, cardiomyocytes grow through eccentric hypertrophy, extending lengthwise but maintaining the same diameter. During heart pressure overload, cardiomyocytes grow through concentric hypertrophy, increasing in diameter but maintaining the same length, resulting in heart wall thickening.
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The left ventricle myocardium is the thickest part of the heart
The heart is made up of three layers of muscle tissue, with cardiac muscle or myocardium forming the thickest layer. The other two layers are the outer epicardium and the inner endocardium. The myocardium is composed of cardiac muscle fibres, which enable the heart to contract.
The thickness of the myocardium determines the strength of the heart's ability to pump blood. The thickness of the myocardium may change in some individuals as a compensatory adaptation to disease, either thickening and becoming stiff or becoming thinner and flabby. Cardiac hypertrophy is a common result of hypertension, in which the cells of the myocardium enlarge as an adaptive response to pumping against higher pressure.
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Cardiomyocytes are the individual cells that make up the cardiac muscle
The cardiac muscle, also known as myocardium, forms the thick middle layer of 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.
The individual 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 organise 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, causing the cell to shorten and fatten. This process is activated by the release of calcium from the sarcoplasmic reticulum when delivering an action potential to the muscle, in a process called excitation-contraction coupling.
The cardiomyocytes are joined together at their ends by intercalated discs to create a syncytium of cardiac cells. Within the intercalated disc, there are three different types of cell junctions: fascia adherens, desmosomes, and gap junctions. The lateral side of the discs contains gap junctions that permit intercellular communication by allowing ions from one cardiomyocyte to move to a neighbouring cell without having to be excreted into the extracellular space first. The low resistance of the gap junctions allows depolarisation to spread quickly throughout the syncytium, facilitating the rapid transmission of action potentials to produce a synchronised contraction of the cardiomyocytes in unison.
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The thickness of the myocardium may change in some individuals as a response to disease
The cardiac muscle, also known as the myocardium, is the thick middle layer of the heart wall. It is surrounded by a thin outer layer called the epicardium or visceral pericardium and an inner endocardium. The thickness of the myocardium varies in different parts of the heart, with the left ventricle being the thickest part. This is because the left ventricle is responsible for generating the power needed to pump oxygenated blood from the heart to the rest of the body.
Additionally, individual cardiomyocytes, which make up the myocardium, can grow in response to heart disease, extensive exercise, or heart muscle injury. Cardiomyocyte hypertrophy occurs through sarcomerogenesis, the creation of new sarcomere units in the cell. During heart volume overload, cardiomyocytes grow through eccentric hypertrophy, becoming longer while maintaining the same diameter. In contrast, during heart pressure overload, cardiomyocytes grow through concentric hypertrophy, increasing in diameter while remaining the same length, resulting in heart wall thickening.
The thickness of the myocardium is crucial for its function, as it enables forceful contractions necessary for pumping blood throughout the body. However, when the myocardium becomes too thick, it can compromise the heart's ability to pump blood effectively, leading to potential heart failure. Therefore, while the thickness of the myocardium may change in response to disease, these adaptations are not always beneficial and can have detrimental consequences for cardiovascular health.
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Frequently asked questions
Yes, cardiac muscle is thick. The myocardium (cardiac muscle) is the thickest section of the heart wall.
The myocardium is the middle layer of the heart wall, composed of cardiac muscle fibres. It is thicker than the outer layer, the epicardium or visceral pericardium, and the inner layer, the endocardium.
The myocardium is responsible for heart contractions, which pump blood around the body. The thickness of the myocardium determines the strength of the heart's ability to pump blood.
The myocardium is made up of individual cardiac muscle cells called cardiomyocytes, which are shorter and have fewer nuclei than skeletal myocytes. These cells are joined by intercalated discs and encased in collagen fibres and other substances that form the extracellular matrix.
The myocardium contracts and releases involuntarily. This is caused by electrical stimulation in the form of a cardiac action potential, which triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum.
