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Cardiac muscle cells, also called cardiomyocytes, are involuntary muscles found only in the heart. They are cylindrical and uninucleated, with branching fibres and striations. This is in contrast to skeletal muscle fibres, which are multinucleated and under voluntary control. Smooth muscle cells, on the other hand, are spindle-shaped, uninucleated, and involuntary.
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What You'll Learn
Cardiac muscle cells are uninucleated
Cardiac muscle cells, also called cardiomyocytes, are uninucleated. They are found only in the heart and are involuntary muscles. Cardiac muscle cells are cylindrical and branched in shape, and they have striations and intercalated discs. The intercalated discs and gap junctions between cardiac muscle cells allow for functional synchronism, which is important for the coordinated contraction of the heart.
The contraction and relaxation of cardiac muscle cells are similar to those of skeletal muscle cells but with some differences. Cardiac muscle cells are specialized excitable cells that can induce electrical impulses and generate action potentials. This electrical excitability of cardiac muscle cells is due to the presence of contractile proteins, such as actin and myosin, which enable the cells to contract and relax rhythmically.
The shape of cardiac muscle cells is also distinct from that of skeletal muscle cells. Skeletal muscle fibers are typically cylindrical, multinucleated, striated, and under voluntary control. In contrast, cardiac muscle cells are branched and cylindrical with a single nucleus per cell. This unique structure and function of cardiac muscle cells are crucial for maintaining the rhythmic contractions of the heart and ensuring efficient blood circulation throughout the body.
It is important to note that smooth muscle cells, which are found within the inner lining of various organs and structures such as the stomach, oesophagus, and blood vessels, are also uninucleated. Smooth muscles are involuntary and have a fusiform shape. They lack striations, which are characteristic of skeletal and cardiac muscle cells. The distinct structural and functional characteristics of cardiac muscle cells, including their uninucleated nature, play a vital role in maintaining the proper functioning of the cardiovascular system.
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Cardiac muscle cells are multinucleated
Cardiac muscle cells are usually mononucleated, meaning they have one nucleus per cell. However, they can occasionally contain two nuclei, leading to the classification of cardiac muscle cells as multinucleated in some sources.
Cardiac muscle cells, also known as cardiomyocytes, are unique in that they are involuntary muscles, meaning their contraction does not depend on an individual's will. They are structurally similar to skeletal muscles but differ in their development process. While skeletal muscles are formed through the fusion of multiple myoblasts (muscle precursor cells), resulting in multinucleated muscle fibres, cardiac myocytes do not fuse together during development. Instead, they remain separate and are connected by intercalated discs and gap junctions, forming a functional synchronism.
The presence of intercalated discs in cardiac muscle cells is significant. These discs, along with transverse tubules, are specialised regions of the cell membrane that contribute to the unique properties of cardiac muscle. The cell membrane, or sarcolemma, plays a crucial role in receiving and conducting stimuli for muscle contraction. The sarcolemma is also involved in anchoring the cell's cytoskeleton, which stabilises the intracellular components and controls the size and shape of the cell.
While cardiac muscle cells are typically considered mononucleated, there is some variation in the number of nuclei. The presence of multiple nuclei in a small number of cardiac muscle cells contributes to the classification of cardiac muscle as multinucleated in certain contexts. However, it is important to note that skeletal muscles, found in bones and attached to tendons, are consistently multinucleated, with their nuclei located at the periphery of the cell.
In summary, cardiac muscle cells are primarily considered mononucleated, but the occasional presence of additional nuclei in some cells leads to their association with multinucleated characteristics.
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Cardiac muscle cells are cylindrical
Cardiac muscle cells, also known as cardiomyocytes, are cylindrical in shape. They are approximately 100 μm long and 10–25 μm in diameter. These cells are found only in the heart and are responsible for the contractility of the heart, which results in the pumping action.
Cardiac muscle cells are branched and cylindrical, and they are uninucleate. The contraction and relaxation of these cells are similar to those of skeletal muscles but with some differences. For instance, cardiac muscle cells are under involuntary control, while skeletal muscles are under conscious control.
Cardiac muscle cells are specialised excitable cells that can induce electrical impulses and give rise to action potentials. These action potentials trigger the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum, leading to excitation-contraction coupling. Gap junctions between adjacent cardiomyocytes allow for the propagation of coordinated action potentials, enabling the heart to pump blood efficiently.
Cardiomyocytes are also capable of growth and hypertrophy. For example, in response to extensive exercise, heart disease, or heart muscle injury, cardiomyocytes can undergo eccentric hypertrophy, where they extend lengthwise while maintaining the same diameter. On the other hand, during heart pressure overload, cardiomyocytes exhibit concentric hypertrophy, increasing in diameter while maintaining their length, which results in heart wall thickening.
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Cardiac muscle cells are branched
Cardiac muscle cells, also called cardiomyocytes, are branched. They are much smaller than skeletal muscle cells, with a diameter of 10-20 μm and a length of 50-100 μm. Cardiac muscle is found only in the heart, forming the contractile walls of the organ.
The branched nature of cardiac muscle cells allows them to form long chains and develop cell junctions, anchoring each cell to its neighbour. These junctions are called intercalated discs, and they connect cardiac muscle cells to one another at their ends. Intercalated discs contain desmosomes and gap junctions, which have important functions. Desmosomes provide a tight mechanical connection between cells, while gap junctions allow action potentials to propagate between cells. This electrical coupling allows the quick transmission of action potentials and the coordinated contraction of the entire heart.
The contraction and relaxation of the cardiac muscle are similar to that of skeletal muscles but with some differences. Cardiac muscle cells are involuntary and have a unique structure. They are cylindrical and uninucleate, with a centrally positioned nucleus. The branched nature of the cells and the presence of gap junctions allow rapid propagation of action potentials across the entire myocardium, enabling the heart to contract and relax as a single unit, or functional syncytium.
The network of electrically connected cardiac muscle cells creates a functional unit of contraction. This network is critical to the coordinated and efficient function of the myocardium during each heartbeat. The pacemaker cells, a group of self-excitable cells, initiate a wave of contraction that allows the heart to work as a unit. These cells can depolarize and fire action potentials at set intervals, determining the heart rate.
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Cardiac muscle cells are involuntary
Cardiac muscle cells, also called cardiomyocytes, are involuntary muscles. They are found only in the heart, specifically in the walls of the heart. They are responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force to pump blood and supply the metabolic demands of the entire body.
Cardiac muscle cells are roughly rectangular in shape when viewed under a microscope. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Each cell contains myofibrils, specialized protein contractile fibers of actin and myosin that slide past each other. The cardiac cells of the heart are specialized excitable cells that are able to induce electrical impulses and give rise to the action potential.
The generation of a cardiac action potential is involuntary and proceeds via a process known as excitation-contraction coupling (ECC). Action potentials travel along the sarcolemma and into the t-tubules to depolarize the membrane. This process triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. The rise in calcium causes the cell's myofilaments to slide past each other.
Specialized modified cardiomyocytes known as pacemaker cells set the rhythm of the heart contractions. They are located in the sinoatrial node (the primary pacemaker) and the atrioventricular node (secondary pacemaker). Pacemaker cells carry the impulses that are responsible for the beating of the heart. They are distributed throughout the heart and are responsible for several functions, including spontaneously generating and sending out electrical impulses.
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Frequently asked questions
No, cardiac muscles are uninucleate, meaning they have one nucleus per cell.
Cardiac muscle cells, also called cardiomyocytes, are cylindrical, striated, and involuntary. They are found only in the heart.
Skeletal muscles are multinucleated, striated, and under voluntary control. They are cylindrical in shape and are found in various parts of the body, unlike cardiac muscles, which are only found in the heart.
Smooth muscles are uninucleated and involuntary. They are fusiform in shape and are found within the inner lining of organs and structures such as the stomach, oesophagus, and intestines.
