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Cardiac muscle, also known as 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. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall and the inner layer. Cardiac muscle cells form a highly branched cellular network in the heart, with each cell containing myofibrils, specialized protein contractile fibres of actin and myosin that slide past each other.
| Characteristics | Values |
|---|---|
| Found in | Heart |
| Muscle type | Striated |
| Muscle category | One of three major categories of muscles found within the human body, along with smooth muscle and skeletal muscle |
| Muscle cells | Branched, smaller than skeletal muscle cells |
| Muscle cell shape | Rectangular |
| Muscle cell size | 10–20 μm in diameter and 50–100 μm in length |
| Muscle cell junctions | Intercalated discs, desmosomes, gap junctions |
| Muscle cell contraction | Rhythmic, involuntary |
| Muscle cell contraction regulation | Sinoatrial node of the heart |
| Muscle cell contraction process | Excitation-contraction coupling |
| Muscle cell contraction energy source | ATP |
| Muscle layer | Thick middle layer of the heart |
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What You'll Learn
Cardiac muscle cells are connected by intercalated discs
Cardiac muscle, or myocardium, is one of three types of muscle in the body, the other two being skeletal and smooth muscle. It forms the thick middle layer of the heart and is responsible for the contractility of the heart and, therefore, the pumping action. The individual cells that make up the cardiac muscle are called cardiomyocytes, and their primary function is to contract, generating the pressure needed to pump blood through the circulatory system.
The intercalated disc at the ends of muscle cells consists of extensive folds and intercellular junctions for mechanical and electrical connections between adjacent cells. Intercalated discs are the major portal for cardiac cell-to-cell communication, which is required for coordinated muscle contraction and maintenance of circulation. The structure of the membrane in the intercalated disc greatly increases the surface area contact between the cells and helps hold the cells together.
Genetic disorders that affect the structure and function of cardiac muscle are termed cardiomyopathies and can lead to heart failure. Mutations in the intercalated disc gene are responsible for various cardiomyopathies. Ruptured intercalated discs, when seen on histopathology, have two main causes: microtome sectioning and forceful myocardial contraction, in turn mainly caused by ventricular fibrillation or electrical injury.
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Cardiomyocytes are rectangular, branching cells
Cardiomyocytes, the individual cells that make up cardiac muscle, are rectangular and branching. Cardiac muscle, also known as myocardium, is one of three types of muscle in the body, the other two being skeletal and smooth muscle. The myocardium is the thick middle layer of the heart, surrounded by a thin outer layer called the epicardium and an inner endocardium.
Cardiac muscle cells are much smaller than skeletal muscle cells, measuring 10-20 μm in diameter and 50-100 μm in length. They are also unique in that they contain intercalated discs that connect cardiac muscle cells to each other. These intercalated discs contain desmosomes and gap junctions, which perform important functions. Desmosomes provide tight mechanical connections between cells, while gap junctions allow action potentials to propagate between cells. The branched nature of the cells and the presence of gap junctions allow for the rapid propagation of action potentials across the entire myocardium, enabling the heart to contract and relax as a single unit.
Cardiomyocytes are the contractile myocytes of the cardiac muscle, and their primary function is to contract, generating the pressure needed to pump blood through the circulatory system. The contraction of cardiomyocytes occurs through the release of calcium from the sarcoplasmic reticulum, which causes the formation of "cross-bridges" between thick and thin myofilaments, resulting in the contraction of the heart and the generation of force.
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Cardiac muscle is striated
Cardiac muscle, also known as 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. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium or epicardium) and the inner layer (the endocardium).
The striated appearance of cardiac muscle is due to the regular arrangement of contractile units (sarcomeres) along the length of the fiber. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. The thick myofilaments contain the protein myosin, while the thin myofilaments contain the protein actin. These myofilaments slide past each other as the muscle contracts and relaxes, producing the formation of "cross-bridges" and causing contraction of the heart and generation of force. The regular organization of myofibrils into sarcomeres gives cardiac muscle cells a striped or striated appearance when viewed through a microscope. These striations are caused by lighter I bands composed mainly of actin, and darker A bands composed mainly of myosin.
Cardiac muscle cells are much smaller (10-20 μm in diameter and 50-100 μm in length) compared to skeletal muscle cells. They are typically single cells with a single, centrally located nucleus, unlike skeletal muscle cells, which often contain many nuclei. Cardiac muscle cells are joined at their ends by intercalated discs to form long fibers. These intercalated discs contain desmosomes and gap junctions, which perform important functions. Desmosomes provide tight mechanical connections between cells, while gap junctions allow action potentials to propagate between cells, enabling the heart to contract and relax as a single unit.
Overall, the striated appearance of cardiac muscle is due to the regular arrangement of contractile proteins and the presence of intercalated discs connecting individual cardiac muscle cells to form long fibers.
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Cardiac muscle is one of three types of muscles
Cardiac muscle, also known as the myocardium, is one of three types of muscles found in the human body. The other two types are smooth muscle and skeletal muscle. Cardiac muscle is located in the walls of the heart and is responsible for the heart's contractility and pumping action. It is composed of sarcomeres, which are the fundamental contractile units of the muscle cells, allowing the heart to contract and pump blood into circulation.
Cardiac muscle cells have a unique structure that sets them apart from other muscle cells. They are rectangular in shape and typically contain a single central nucleus. They appear striped or striated due to the arrangement of contractile units along the length of the fiber. The cardiac muscle fibers branch and are interconnected by intercalated discs, which facilitate a synchronized heartbeat. These intercalated discs contain desmosomes and gap junctions, which play important roles in maintaining the structural integrity of the heart and allowing for the propagation of electrical signals between muscle cells.
Unlike skeletal muscle, cardiac muscle is under involuntary control. This means that it contracts and relaxes without conscious effort, generating a strong, rhythmic, and coordinated heartbeat. The contractile functions of the cardiac muscle require a constant supply of oxygen, nutrients, and ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The process of contraction and relaxation involves the release of calcium from the sarcoplasmic reticulum and the sliding of actin and myosin filaments past each other, resulting in the formation of cross-bridges and the generation of force.
In summary, cardiac muscle is a vital component of the human body, responsible for the contractility and pumping action of the heart. Its unique structure, including the branched fibers and intercalated discs, allows for synchronized and coordinated contractions, ensuring a steady supply of blood to meet the metabolic demands of the entire body.
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Coronary arteries supply cardiac muscle with blood
The cardiac muscle, or myocardium, is the thick middle layer of the heart. It is one of three types of muscles in the body, the other two being smooth muscle and skeletal muscle. The myocardium is surrounded by a thin outer layer called the epicardium and an inner endocardium.
The coronary arteries supply blood to the cardiac muscle. They are the first branches of the aortic root, which is the first part of the aorta that emerges from the left ventricle of the heart. The coronary arteries wrap around the outside of the heart and smaller branches dive into the heart muscle to bring it blood. The two main coronary arteries are the right coronary artery (RCA) and the left main coronary artery (LMCA). Each of these arteries contains smaller branches that go deep inside the heart muscle.
The RCA supplies blood to the right ventricle and the right atrium, where deoxygenated blood goes before heading to the lungs. The LMCA supplies blood to the left ventricle and the left atrium, where oxygenated blood arrives from the lungs before being pumped out to the rest of the body. The LMCA branches off to give the left circumflex coronary artery (LCX) and the left anterior descending artery (LAD). The circumflex artery supplies blood to the outer side and back of the heart, while the LAD supplies blood to the front of the left side of the heart.
The coronary arteries supply the heart muscles with the oxygen and nutrients they need to pump blood through the body. The cardiac muscle is responsible for the contractility of the heart and must contract with enough force to supply the metabolic demands of the entire body. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
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Frequently asked questions
Cardiac muscles are one of the three major categories of muscles found within the human body, the other two being smooth muscle and skeletal muscle. They are found only in the heart and are responsible for the heart's pumping action.
Cardiomyocytes are the individual cells that make up the cardiac muscle. They are rectangular, branching cells that typically contain only one centrally-located nucleus.
While both cardiac and skeletal muscles are striated and multinuclear, cardiac muscle cells may be branched instead of linear and longitudinal as in skeletal muscle cells. Additionally, cardiac muscle is under involuntary control, unlike skeletal muscle.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
The rhythmic contraction of cardiac muscle is regulated by the sinoatrial node of the heart, which serves as the heart’s pacemaker. Electrical stimulation triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum, which causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling.
