Logan Steele
Cardiac muscle, also known as 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 tissue. Cardiac muscle tissue is only found in the heart and is responsible for keeping the heart pumping and blood circulating around the body. The muscle tissue contains cells that expand and contract in response to electrical impulses from the nervous system. These cardiac cells work together to produce the rhythmic, wave-like contractions known as the heartbeat.
| Characteristics | Values |
|---|---|
| Types | One of three types of muscle tissues, the others being skeletal muscle and smooth muscle |
| Location | Found only in the heart |
| Involuntary control | Yes |
| Composition | Individual cardiac muscle cells or cardiomyocytes joined by intercalated discs, encased by collagen fibers and other substances that form the extracellular matrix |
| Contraction | Rhythmic, wave-like contractions that allow the heart to pump blood through the circulatory system |
| Calcium | Rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling |
| T-tubules | Bigger and wider than those in skeletal muscle, but fewer in number |
| Pacemaker cells | Set the rhythm of the heart contractions |
| Sarcomeres | Contractile units that allow for contractility |
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What You'll Learn
Cardiac muscle is one of three types of muscle tissues
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle, also called heart muscle or myocardium, is found only in the heart. It is one of three major categories of muscles in the human body. The other two types of muscle tissues are skeletal muscle and smooth muscle.
Cardiac muscle is made up of sarcomeres that allow for contractility. The heart consists mostly of cardiac muscle cells (or myocardium). 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 endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells and forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium.
Cardiac muscle tissue contracts and releases involuntarily and keeps the heart pumping blood around the body. 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 rate at which the heart contracts and the synchronization of atrial and ventricular contraction are required for the efficient pumping of blood. The heart rate is determined by the contractile force developed by the cardiac muscle cells, as well as by the frequency at which they are activated (rhythmicity).
Cardiac muscle cells or cardiomyocytes are striated, branched, and contain many mitochondria. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess.
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It is also called myocardium
Cardiac muscle, also called myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is found only in the heart. 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 myocardium is composed of cardiac muscle cells or cardiomyocytes, which are striated, branched, and contain many mitochondria. These cells are joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The intercalated discs contain gap junctions (adhesions that facilitate fast cell-to-cell communication), allowing for the propagation of coordinated action potentials from one cell to the next in a phenomenon known as electrical coupling.
The myocardium functions as a syncytium with synchronized contraction. The main function of the myocardium is to facilitate the contraction and relaxation of the heart walls in order to receive and pump blood into the systemic circulation. The contraction of the myocardium allows 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.
The heart is made up of three layers: the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells that form the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium.
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Cardiac muscle is involuntary
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 heart is made up of three layers—the pericardium, myocardium, and endocardium. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells and forms the inner lining of the heart chambers and valves.
Cardiac muscle cells (cardiomyocytes) are striated, branched, contain many mitochondria, and are under involuntary control. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The mechanism behind each coordinated contraction involves the cardiac muscle and electrical impulses. These contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
Cardiac muscle tissue works to keep the heart pumping and blood circulating around the body. The tissue contains cells that expand and contract in response to electrical impulses from the nervous system. These cardiac cells work together to produce the rhythmic, wave-like contractions known as the heartbeat.
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It is made up of sarcomeres
Cardiac muscle, also known as heart muscle or myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. Cardiac muscle is made up of sarcomeres, which are contractile units that give the muscle its striated appearance.
Sarcomeres are composed of two main protein filaments, actin and myosin, which are responsible for muscular contraction. Actin is the thin filament, while myosin is the thick filament. These filaments are integrated in a paracrystalline order by accessory cytoskeleton proteins, forming the sarcomeric cytoskeleton. The interaction between actin and myosin filaments is based on the sliding filament model, where the actin filaments slide past the myosin filaments, resulting in contraction. This sliding movement is described as a "molecular dance", with the myosin reaching forward to bind to the actin, contracting, and then releasing it.
The length of a sarcomere decreases during contraction, shortening like a collapsing telescope as the actin filaments slide towards the centre of the myosin filament. This contraction is known as the power stroke and requires the hydrolysis of ATP (Adenosine triphosphate). The force generated by a single sarcomere is small, but when many sarcomeres contract simultaneously, they produce a powerful force that shortens the entire muscle.
The structure of a sarcomere includes several distinct regions, including the I-band, A-band, H-zone, M-line, and Z-line. The I-band is the zone of thin filaments (actin) that are not superimposed by thick filaments, while the A-band contains the entire thick filament (myosin) as well as the ends of the actin filaments. The H-zone is the area between the M-line and Z-disc that contains only the myosin. The M-line marks the centre of the sarcomere and contains the protein myomesin. The Z-line, or Z-disc, is formed by the actin filaments and separates neighbouring sarcomeres.
The sarcomere structure also includes important proteins such as titin and nebulin, which provide elasticity and act as molecular rulers for filament assembly. The interaction between the proteins and filaments within the sarcomere contributes to its contractile function and overall muscle performance.
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The heart is made up of three layers
The heart is a muscular organ that pumps blood throughout the body. It is housed in a protective sac called the pericardium, which also contains a small amount of fluid. The heart wall is made up of three layers: the outer epicardium, the middle myocardium, and the inner endocardium.
The epicardium, or the outer layer of the heart wall, is also known as the visceral pericardium as it forms the inner layer of the pericardium. It is composed primarily of loose connective tissue, including elastic fibres and adipose tissue. The epicardium functions to protect the inner heart layers and assists in the production of pericardial fluid, which helps reduce friction between the pericardial membranes. The coronary blood vessels, which supply the heart wall with blood, are also found in this layer.
The myocardium is the thickest layer of the heart wall, with its thickness varying in different parts of the heart. It is composed of cardiac muscle fibres, which enable the heart to contract and pump blood. 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.
The endocardium is the thin inner layer of the heart wall. It lines the inner heart chambers, covers the heart valves, and is continuous with the endothelium of the veins and arteries of the heart. The endocardium of the heart atria consists of smooth muscle and elastic fibres. An infection of the endocardium can lead to a serious and potentially fatal condition known as endocarditis.
Small lymphatic networks called plexuses exist beneath each of these three layers of the heart. These networks collect into a main left and right trunk, which travel up the groove between the ventricles and receive smaller vessels as they move upwards.
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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 and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart.
Cardiac muscle tissue forms the heart and keeps it pumping blood around the body. It performs involuntary, rhythmic and coordinated contractions that allow the heart to pump blood through the circulatory system.
Cardiac muscle cells (cardiomyocytes) are surrounded by an extracellular matrix produced by supporting fibroblast cells. They contain contractile units known as sarcomeres and are joined by intercalated discs. Electrical stimulation triggers the release of calcium from the cell's internal store, which causes the cell's myofilaments to slide past each other, resulting in contraction.
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