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There are three types of muscle tissue in the human body: cardiac, smooth, and skeletal. The cardiac muscle, also called the myocardium, is the involuntary, striated muscle that forms the thick middle layer of the heart wall. The striations in the cardiac muscle are due to the arrangement of contractile units (sarcomeres) along the length of the fiber. The contractile stimuli in the cardiac muscle are propagated from one cell to the next, resulting in a synchronous contraction of the entire tissue section.
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What You'll Learn
- Cardiac muscle cells are striated and under involuntary control
- Striations are caused by the arrangement of contractile units (sarcomeres)
- Cardiac muscle forms a thick middle layer of the heart wall
- Cardiomyocytes are joined by intercalated discs
- Contracting heart muscle requires a constant flow of blood to provide oxygen and nutrients
Cardiac muscle cells are striated and under involuntary control
The human body is made up of four basic types of tissues, one of which is muscle tissue. There are three types of muscle tissue: cardiac, smooth, and skeletal. Cardiac muscle tissue forms the bulk of the heart and is located in the walls of the heart. It is involuntary and striated.
Cardiac muscle cells are striated due to the arrangement of contractile units (sarcomeres) along the length of the fiber. Sarcomeres are repeating functional units that are visible along muscle fibers, giving a striated appearance to the tissue. The striations in cardiac muscle arise due to the arrangement of contractile units (sarcomeres) along the length of the fiber. The two types of striated muscle are skeletal muscle and cardiac muscle.
Cardiac muscle cells are under involuntary control by the body's autonomic nervous system (ANS). Autorhythmic cardiac cells do not contract; they set the pace of contraction for other cardiac muscle cells, which the ANS can modulate. The contractile cardiac cells (cardiomyocytes) constitute the majority of the heart muscle and can contract. The contractions in cardiac muscle will pump blood throughout the body.
Cardiac muscle cells are joined together via intercalated discs, which coincide with Z lines. They appear as lines that run perpendicular to the muscle fibers when examined with a light microscope. The intercalated discs allow cardiac muscle tissue to function as a functional syncytium. The contractile stimuli are propagated from one cell to the next, resulting in a synchronous contraction of the entire tissue section.
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Striations are caused by the arrangement of contractile units (sarcomeres)
Cardiac muscle tissue is one of the three types of muscle tissue, the other two being smooth and skeletal. It is located in the walls of the heart and is under involuntary control. Cardiac muscle tissue is striated, which means that it has a striped appearance.
Striations are caused by the arrangement of contractile units called sarcomeres. Sarcomeres are the smallest functional units of a muscle fiber and are composed of actin and myosin filaments. These filaments are arranged in a repeating pattern, with each sarcomere containing one entire "A band" and two halves of an "I band", one on either side of the A band. The A band is composed of thick filaments of myosin, while the I band contains thin actin filaments. During muscle contraction, the actin and myosin filaments slide over each other, causing the sarcomeres to shorten and the muscle to contract.
In cardiac muscle tissue, the myofilaments are arranged in a similar pattern to skeletal muscle, resulting in cross-striations. The fibers are crossed by linear bands called intercalated discs, which provide attachment points and allow the tissue to function as a syncytium. The intercalated discs coincide with Z-lines, which are the borders between sarcomeres. The actin filaments of terminal sarcomeres insert into these junctions, allowing the transmission of force from cell to cell during contractions.
The striated appearance of cardiac muscle tissue is, therefore, due to the arrangement of contractile units called sarcomeres, which are composed of actin and myosin filaments. These filaments slide over each other during muscle contraction, causing the sarcomeres to shorten and resulting in the characteristic striated appearance of cardiac muscle tissue.
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Cardiac muscle forms a thick middle layer of the heart wall
The heart is a muscular organ that pumps blood throughout the body. It is housed in the pericardial sac, which protects it and assists with its mechanics. The heart is made up of three layers of tissue: the outer layer, known as the epicardium, the myocardium, which forms the middle layer, and the endocardium, the innermost layer.
The myocardium is the thickest layer of the heart wall and is made up of cardiac muscle fibres, which enable the heart to contract. The thickness of the myocardium varies in different parts of the heart. It is thicker in the ventricles than in the atria due to the greater hydrostatic pressure that the ventricles must overcome when pumping blood into the systemic vessels. The myocardium is a working muscle that requires a constant supply of oxygen and nutrients to function efficiently. As a result, cardiac muscle has an extensive network of blood vessels to deliver oxygen to the contracting cells and remove waste products.
Cardiac muscle cells are located in the walls of the heart and appear striped or striated. They are under involuntary control. The myofilaments of cardiac muscle are arranged in a similar pattern to skeletal muscle, resulting in cross-striations. The fibres are crossed by linear bands called intercalated discs, which provide attachment points, giving the tissue a branched pattern. Intercalated discs also allow cardiac muscle tissue to function as a functional syncytium, enabling contractile stimuli to be propagated from one cell to the next, resulting in a synchronous contraction of the entire tissue section.
Cardiac muscle cells usually contain one elongated nucleus that lies in the centre, which helps to distinguish them from skeletal muscle cells, which have multiple nuclei dispersed in the periphery of the cell.
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Cardiomyocytes are joined by intercalated discs
Cardiac muscle tissue, or cardiomyocytes, are characterised by their striated appearance. They are located in the walls of the heart and are under involuntary control. The myofilaments of cardiac muscle are arranged in a similar pattern to skeletal muscle, resulting in cross-striations. These striations are visible under a microscope and give the tissue its distinctive appearance.
Cardiac muscle cells are joined together by intercalated discs, which are linear bands that cross the fibres of cardiac muscle. These discs provide attachment points, giving the tissue a branched pattern. They also allow the cardiac muscle tissue to function as a syncytium, enabling the contractile stimuli to be propagated from one cell to the next, resulting in a synchronous contraction of the entire tissue section.
Intercalated discs are complex structures that connect adjacent cardiac muscle cells. They are composed of three types of cell junctions: desmosomes, fascia adherens junctions, and gap junctions. Desmosomes act as anchoring sites, preventing separation during contraction by binding intermediate filaments. Fascia adherens junctions are responsible for connecting the ends of the cardiomyocytes together to form a fibre, as well as transmitting the force of contractions from cell to cell. Gap junctions, on the other hand, provide the electrochemical connection between neighbouring cardiac muscle cells, allowing cardiac action potentials to spread between cells and enabling the depolarization of the heart muscle.
The intercalated discs in cardiac muscle tissue were first observed in the 19th century through light microscopy. However, it was not until the advent of electron microscopy in 1966 that the detailed nanostructure of these discs was revealed. Today, intercalated discs are recognised as dynamic "organelles" that play a crucial role in maintaining the health of cardiac muscle tissue.
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Contracting heart muscle requires a constant flow of blood to provide oxygen and nutrients
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. The cardiac muscle (myocardium) forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
The myofilaments of cardiac muscle are arranged in a similar pattern to skeletal muscle, resulting in cross-striations. The fibres are crossed by linear bands called intercalated discs, which provide attachment points and allow cardiac muscle tissue to function as a functional syncytium. The contractile stimuli propagate from one cell to the next, resulting in a synchronous contraction of the entire tissue section.
Cardiac muscle contraction occurs via excitation-contraction coupling (ECC), which utilises a mechanism called calcium-induced calcium release (CICR). ECC is the process of converting an electrical stimulus (AP) into a mechanical response (muscle contraction). CICR involves the conduction of calcium ions into the cardiomyocyte, leading to the further release of ions into the cytoplasm. Calcium causes the cell's myofilaments to slide past each other, and the binding of the myosin head to ATP pulls actin filaments to the centre of the sarcomere, creating the mechanical force of contraction.
Contracting heart muscle uses a lot of energy and requires a constant flow of blood to provide oxygen and nutrients. Blood is brought to the myocardium by the coronary arteries, which originate from the aortic root and lie on the outer or epicardial surface of the heart. The most important factor affecting the function of the cardiac muscle is inadequate oxygenation, usually the result of an inadequate coronary artery supply.
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Frequently asked questions
Yes, cardiac muscle is an involuntary, striated muscle.
Striations are repeating functional units called sarcomeres that are visible along muscle fibres, giving a striated appearance to the tissue.
The striations in skeletal and cardiac muscle arise due to the arrangement of contractile units (sarcomeres) along the length of the fibre. However, the fibres of skeletal muscle have a cylindrical shape with blunt ends, while those in cardiac muscle are crossed by linear bands called intercalated discs.
The main function of striated muscle tissue is to create force and contract. In cardiac muscle, these contractions pump blood throughout the body.
