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Cardiac muscle is a type of striated muscle found only in the heart and is responsible for the heart's ability to pump blood. It is characterized by a similar arrangement of actin and myosin filaments to mediate contraction. An interesting fact about cardiac muscle is that it is typically mononucleated, meaning there is one nucleus per cell, but it can sometimes have two nuclei. This is in contrast to skeletal muscle, which consists of long multinucleate fibers. The cardiac muscle is the most hard-working muscle in the human body, contracting and relaxing 60-100 times per minute from intrauterine life until death, often without rest.
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What You'll Learn
Cardiac muscle is a type of striated muscle
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 tissue found only in the heart and is responsible for the ability of the heart to pump blood. The cardiac muscle constitutes the main tissue of the wall of the heart. It forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium), with blood supplied via the coronary circulation.
Cardiac muscle, like skeletal muscle, is made up of sarcomeres that allow for contractility. However, unlike skeletal muscle, cardiac muscle is under involuntary control. The heart is made up of three layers—pericardium, myocardium, and 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. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force and blood to supply the metabolic demands of the entire body.
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. Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
The molecular basis of contraction of cardiac muscle is very similar to that of skeletal muscle. Contraction of cardiac muscle cells is regulated by cytosolic Ca2+ ion concentration in a manner virtually identical to that for skeletal muscle. The cardiac muscle transverse (T) tubular system consists of much wider invaginations of the cell surface. Sarcoplasmic reticulum associated with the T tubules is neither as regular nor as well-organized as in skeletal muscle. The association of cardiac sarcoplasmic reticulum with T tubules takes the form of dyads rather than triads, and is located in the region of the Z lines rather than the AI junction.
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Cardiac muscle cells are mononuclear
Cardiac muscle cells are mononucleated, meaning there is one nucleus per cell. This is in contrast to skeletal muscle cells, which are multinucleated, with long fibres formed from the fusion of thousands of precursor cells. Smooth muscle cells are also mononucleated.
Cardiac muscle is a type of striated muscle, characterised by a similar arrangement of actin and myosin filaments to mediate contraction. It is found only in the heart and is responsible for the heart's ability to pump blood. The cardiac muscle is the most hard-worked muscle in the body, contracting and relaxing 60-100 times per minute from intrauterine life until death, which is often 80-90 years later.
The molecular basis of contraction in cardiac muscle cells is very similar to that of skeletal muscle cells. The contraction of cardiac muscle cells is regulated by cytosolic Ca2+ ion concentration in a manner virtually identical to that of skeletal muscle cells. However, there are some differences between the two types of muscle cells. For example, the cardiac muscle transverse (T) tubular system consists of much wider invaginations of the cell surface, and the sarcoplasmic reticulum associated with the T tubules takes the form of dyads rather than triads.
Cardiac muscle cells are much shorter than skeletal muscle cells. Long cardiac muscle fibres are produced by linking numerous cardiac muscle cells end-to-end via anchoring-type cell junctions. The cells are linked into long chains by specialised cell junctional systems.
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Cardiac muscle fibres are long
Cardiac muscle cells, also called cardiomyocytes, are the contracting cells that allow the heart to pump. They are a type of striated muscle and are characterised by a similar arrangement of actin and myosin filaments to mediate contraction. However, unlike skeletal muscle, cardiac muscle is 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, specialised ion channels that skeletal muscle does not possess. The contraction of cardiac muscle cells is regulated by cytosolic Ca2+ ion concentration in a manner virtually identical to that for skeletal muscle.
The cardiac muscle is the most hard-working muscle in the body. It contracts and relaxes 60-100 times per minute from intrauterine life until death, often 80-90 years later, without rest. Stress and physical activity can increase the number of beats per minute to well above 120, often for long periods. The cardiac muscle in the wall of the left ventricle has a particularly heavy workload, as it must force oxygenated arterial blood around the body.
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Cardiac muscle cells are involuntary
Cardiac muscle cells are indeed mononucleated. They are also involuntary muscles, located in the walls of the heart, and are responsible for the heart's ability to pump blood. This tissue is called involuntary because its movement is not consciously controlled.
Cardiac muscle is a type of striated muscle, appearing striped due to the arrangement of actin and myosin filaments that mediate contraction. These filaments slide past each other as the muscle contracts and relaxes, forming "cross-bridges" that cause the heart to contract and generate force. This process is activated by the release of calcium from the sarcoplasmic reticulum, which delivers an action potential to the muscle in a process called excitation-contraction coupling.
The cardiac muscle is the most hard-working muscle in the human body, contracting and relaxing 60-100 times per minute from intrauterine life until death, which can be 80-90 years later. This constant movement requires a consistent supply of oxygen and nutrients to meet the energy demands of the cardiac muscle. The most important factor affecting the function of the cardiac muscle is inadequate oxygenation, usually due to an inadequate coronary artery supply.
The individual cardiac muscle cell, or cardiomyocyte, is a tubular structure composed of chains of myofibrils. These myofibrils are the rod-like units within the cell that consist of repeating sections of sarcomeres, the fundamental contractile units of the muscle cells. The cardiac muscle transverse (T) tubular system consists of invaginations of the cell surface that contain proteins like L-type calcium channels, sodium-calcium exchangers, and calcium ATPases, which allow for the exchange of ions with extracellular fluid surrounding the cell.
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Cardiac muscle cells have a striped pattern under a microscope
Cardiac muscle cells, found only in the heart, are mononucleated and have a striped pattern under a microscope. This striated pattern is caused by the arrangement of the filaments that comprise myosin and actin proteins within the muscle cells. The dark stripes indicate thick filaments that comprise myosin proteins, while the thin, lighter stripes indicate actin filaments.
When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments towards each other, causing the cell to shrink. This process is powered by adenosine triphosphate (ATP), which is produced by mitochondria within the cardiac muscle cells. These mitochondria are known as the "powerhouses of the cells" as they convert oxygen and glucose into energy.
The contraction of cardiac muscle cells is involuntary and occurs in response to electrical impulses from the nervous system. This process is mediated by ""pacemaker" cells, which generate electrical impulses that tell cardiac muscle cells to contract and relax. The pacemaker cells control the heart rate and determine how fast the heart pumps blood.
Cardiac muscle cells are highly coordinated and work together to produce the rhythmic, wave-like contractions known as the heartbeat. This process is similar to the contraction of skeletal muscle, which is also a type of striated muscle. However, skeletal muscle contractions are usually under conscious control, while cardiac muscle contractions are not.
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Frequently asked questions
Yes, cardiac muscle cells are usually mononucleated, meaning they have one nucleus per cell. However, they can sometimes have two nuclei.
Cardiac muscle cells, found only in the heart, operate involuntarily and never tire throughout life. They are striated, exhibiting a striped pattern under a microscope. They also have intercalated discs, which are specialized cell junctions that facilitate rapid and uniform contraction, ensuring the heart can pump blood effectively and consistently.
Cardiac muscle cells are mononuclear and much shorter than skeletal muscle cells. Cardiac muscle cells are also involuntary, while skeletal muscle cells are voluntary.
Stress and physical activity can increase the number of beats per minute to well above 120, often for long periods. The cardiac muscle in the wall of the left ventricle has a heavy workload as it must force oxygenated arterial blood around the body. Inadequate oxygenation, usually due to an inadequate coronary artery supply, can affect the function of the cardiac muscle.
