Logan Steele
Muscle tissue is classified into three types: striated (skeletal), smooth, and cardiac. Cardiac muscle, also known as myocardium, is a structurally and functionally unique subtype of muscle tissue located in the heart. 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) and the inner layer (the endocardium). The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope.
| Characteristics | Values |
|---|---|
| Type | Cardiac, smooth, and skeletal are the three types of muscle tissue |
| Location | Located in the heart |
| Appearance | Striated |
| Control | Involuntary |
| Composition | Individual cardiac muscle cells joined by intercalated discs |
| Cell shape | Rectangular |
| Cell size | 100–150μm by 30–40μm |
| Cell composition | Myofibrils, actin, myosin, sarcomeres |
| Cell junctions | Intercalated discs |
| Cell nuclei | Single |
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What You'll Learn
- Cardiac muscle cells have a striped or striated appearance under a microscope
- Striations are caused by lighter I bands and darker A bands
- Cardiac muscle is involuntary and constitutes the main tissue of the heart wall
- Cardiomyocytes contract in a coordinated manner, allowing the ventricle to squeeze in several directions
- Cardiac muscle cells are joined at their ends by intercalated discs to form long fibres
Cardiac muscle cells have a striped or striated appearance under a microscope
Cardiac muscle cells, also known as cardiomyocytes, have a striped or striated appearance under a microscope. This unique subtype of muscle tissue is located in the heart and constitutes the main tissue of the heart wall. It is one of the three types of vertebrate muscle tissues, the other two being skeletal muscle and smooth muscle.
Cardiac muscle cells are joined at their ends by intercalated discs to form long fibres. Each cell contains myofibrils, which are specialised protein contractile fibres of actin and myosin that slide past each other. These are organised into sarcomeres, the fundamental contractile units of muscle cells. The regular organisation of myofibrils into sarcomeres gives cardiac muscle cells their striped or striated appearance under a microscope. These striations are caused by lighter I bands composed mainly of actin and darker A bands composed primarily of myosin.
The sarcomeres are the functional subunits of myofibrils and the contractile units of cardiac muscle tissue. They are arranged into a branched pattern, forming a 3D network in the cytoplasm. The thick filaments are made from the protein myosin, while the thin filaments consist of polymers of the protein alpha-actin. These two lines, along with the A band that corresponds to the length of the myosin filaments, are electron-rich and appear darker in electron microscopy. The I and H bands, on the other hand, appear lighter as they represent regions consisting of only thin or thick filaments, but not both.
The cardiac muscle, or 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 composed of individual cardiac muscle cells joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The sheets of muscle that wrap around the left ventricle closest to the endocardium are oriented perpendicularly to those closest to the epicardium. When these sheets contract in a coordinated manner, they allow the ventricle to squeeze in several directions simultaneously – longitudinally, radially, and with a twisting motion – to squeeze the maximum possible amount of blood out of the heart with each heartbeat.
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Striations are caused by lighter I bands and darker A bands
Cardiac muscle, also known as myocardium, is one of the three types of vertebrate muscle tissues, the other two being skeletal muscle and smooth muscle. Cardiac muscle is an involuntary, striated muscle that forms the main tissue of the heart wall.
Striated muscles, such as skeletal muscle, have a distinctive appearance due to the arrangement of protein filaments within them. These muscles contain light and dark bands that result from the interplay between two types of protein: actin and myosin. The light bands are known as I bands, while the dark bands are referred to as A bands. The I bands consist primarily of actin filaments, which are thinner and appear lighter under a microscope. Conversely, the A bands contain myosin filaments, which are thicker and give a darker appearance. The alternating light and dark bands create the striated look of these muscle fibres.
In cardiac muscle, the regular organisation of myofibrils, which are composed of actin and myosin, into sarcomeres gives the muscle its striated appearance. These striations are caused by lighter I bands, composed mainly of actin, and darker A bands, composed mainly of myosin. Each I band is bordered by Z lines or Z discs, which define the boundaries of individual sarcomeres, the functional units of muscle contraction. The space between two consecutive Z discs constitutes a sarcomere, which contains one dark A band flanked by two lighter I bands.
The striated appearance of skeletal muscle tissue is due to repeating bands of the proteins actin and myosin that are present along the length of myofibrils. Dark A bands and light I bands repeat along the myofibrils, and the alignment of myofibrils in the cell causes the entire cell to appear striated or banded.
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Cardiac muscle is involuntary and constitutes the main tissue of the heart wall
Cardiac muscle, also known as myocardium or cardiomyocytes, 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 heart wall.
The cardiac muscle forms a thick middle layer of the heart wall, between the outer layer (the pericardium or epicardium) and the inner layer (the endocardium). The heart wall is a three-layered structure, with the myocardium making up the bulk of the heart. The cardiac muscle is composed of individual cardiac muscle cells joined by intercalated discs, encased by collagen fibres and other substances that form the extracellular matrix.
Cardiac muscle cells are roughly rectangular when viewed through a microscope. They contain myofibrils, which are specialised protein contractile fibres of actin and myosin that slide past each other. These are organised into sarcomeres, the fundamental contractile units of muscle cells. The regular organisation of myofibrils into sarcomeres gives cardiac muscle cells their striated appearance when viewed through a microscope, similar to skeletal muscle. These striations are caused by lighter I bands composed mainly of actin, and darker A bands composed mainly of myosin.
Cardiomyocytes are single cells with a single, centrally located nucleus, unlike skeletal muscle cells, which have many nuclei. They attach to one another with specialised cell junctions called intercalated discs, forming long, branching cardiac muscle fibres. These attachments allow the cells to function as a syncytium, enabling them to synchronise their actions and contract in unison. The contractions of the cardiac muscle pump blood through the body and are under involuntary control.
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Cardiomyocytes contract in a coordinated manner, allowing the ventricle to squeeze in several directions
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) and the inner layer (the endocardium).
Cardiac muscle cells, also known as cardiomyocytes, are the contracting cells that allow the heart to pump. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, working to efficiently pump blood from the heart. Cardiomyocytes contain T-tubules, pouches of cell membrane that run from the cell surface to the cell's interior, which help to improve the efficiency of contraction. The majority of these cells contain only one nucleus, unlike skeletal muscle cells, which contain many nuclei.
Cardiomyocytes attach to one another with specialised cell junctions called intercalated discs. Attached cells form long, branching cardiac muscle fibres that are, essentially, a mechanical and electrochemical syncytium, allowing the cells to synchronise their actions. The cardiac muscle pumps blood through the body and is under involuntary control. The attachment junctions hold adjacent cells together across the dynamic pressure changes of the cardiac cycle.
Within the myocardium, there are several sheets of cardiac muscle cells or cardiomyocytes. The sheets of muscle that wrap around the left ventricle closest to the endocardium are oriented perpendicularly to those closest to the epicardium. When these sheets contract in a coordinated manner, they allow the ventricle to squeeze in several directions simultaneously – longitudinally (becoming shorter from apex to base), radially (becoming narrower from side to side), and with a twisting motion (similar to wringing out a damp cloth) to squeeze the maximum possible amount of blood out of the heart with each heartbeat.
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Cardiac muscle cells are joined at their ends by intercalated discs to form long fibres
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) and the inner layer (the endocardium).
Cardiac muscle cells, also known as cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are located in the walls of the heart and appear striped (striated) under a microscope. These cells are joined at their ends by intercalated discs to form long fibres. Intercalated discs have both anchoring junctions and gap junctions. The attached cells form long, branching cardiac muscle fibres that are a mechanical and electrochemical syncytium, allowing the cells to synchronize their actions.
Each cardiac muscle cell contains myofibrils, specialized protein contractile fibres of actin and myosin that slide past each other. These are organized into sarcomeres, the fundamental contractile units of muscle cells. The regular organization of myofibrils into sarcomeres gives cardiac muscle cells their 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.
Cardiomyocytes contain T-tubules, pouches of cell membrane that run from the cell surface to the cell's interior, which help to improve the efficiency of contraction. They also usually contain one elongated nucleus that lies in the centre, a distinguishing feature from skeletal muscle.
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Frequently asked questions
Cardiac muscle, also known as myocardium or heart muscle, 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 is structurally and functionally unique. It has characteristics from both skeletal and smooth muscle tissues. Unlike skeletal muscle, it is involuntary, and unlike smooth muscle, it is striated. Cardiac muscle also has a single nucleus, whereas skeletal muscle has many.
Cardiac muscle pumps blood through the body. It is capable of strong, continuous, and rhythmic contractions that are automatically generated.
