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Cardiac muscle cells, also known as cardiomyocytes, are found only in the heart. They are involuntary muscles with unique properties that distinguish them from skeletal muscles. Cardiac muscle cells are usually mononucleated, meaning they have one nucleus per cell, but can sometimes have two nuclei. Smooth muscle cells, on the other hand, are mononucleate cells that are either isolated or grouped in layers in various tissues. Skeletal muscle cells, or muscle fibers, have multiple nuclei located at the periphery of the cell, allowing for fast contraction.
| Characteristics | Values |
|---|---|
| Cardiac muscle cells | Mononucleate striated cells |
| Cardiac muscle shape | Branched and cylindrical |
| Cardiac muscle location | Found only in the heart |
| Cardiac muscle type | Involuntary |
| Cardiac muscle function | Generation of movement and force in a specific direction |
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What You'll Learn
Cardiac muscle cells are mononucleated
Cardiac muscle cells, also called cardiomyocytes, are usually mononucleated, meaning there is one nucleus per cell. However, they can sometimes contain two nuclei. Cardiac muscle cells are striated, with fast, rhythmic, spontaneous contractions. They are branched and cylindrical in shape. They are also known as involuntary muscles and are only found in the heart.
Cardiac muscle cells are distinct from skeletal muscle cells, which are multinucleated and are responsible for voluntary movements. Skeletal muscles can be controlled consciously and are characterised by a striated appearance, fast contraction, and the ability to tire easily. An example of a skeletal muscle is the biceps brachii in the upper arm.
The unique structure of skeletal muscles, with multiple nuclei located at the periphery of the cell, helps meet the high energy and protein synthesis requirements for muscle contraction. This multinucleation occurs due to the fusion of myoblasts (muscle precursor cells) during development.
Smooth muscle cells are also mononucleated. They are found within the inner lining of various organs and structures such as the stomach, oesophagus, bronchi, uterus, intestines, urethra, urinary bladder, and blood vessels. Smooth muscle contractions are slow and depend on the autonomic nervous system.
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Cardiac muscle cells are multinucleated
Cardiac muscle cells, also called cardiomyocytes, are typically mononucleated, meaning there is one nucleus per cell. However, there are some instances where cardiac muscle cells can have two nuclei. Cardiac muscle cells are striated, with fast, rhythmic, spontaneous contractions. They are branched and cylindrical in shape and are found only in the heart.
Cardiac muscle cells are distinct from skeletal muscle cells, which are typically multinucleated and found in muscles like the biceps brachii in the upper arm. Skeletal muscles are under voluntary control, meaning we can consciously control their movement. They also have a striated appearance, with a striped pattern visible under a microscope. Additionally, they can contract quickly but can also tire easily.
Smooth muscle cells, on the other hand, are mononucleate and found within the inner lining of various organs and structures such as the stomach, oesophagus, bronchi, uterus, intestines, urethra, urinary bladder, and blood vessels. Smooth muscle contractions are slow and depend on the autonomic nervous system. They are fusiform in shape and are not under conscious control like skeletal muscles.
While cardiac muscle cells are typically mononucleated, there is some debate and conflicting information on the internet regarding their structure. Some sources indicate that cardiac muscle cells can be multinucleated, while others state that they are exclusively mononucleated. Further scientific research and consensus are needed to definitively resolve this discrepancy.
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Cardiac muscle cells are branched and cylindrical
Cardiac muscle cells, also called cardiomyocytes, are branched and cylindrical in shape. They are found only in the heart and are joined to one another by intercalated discs. These discs contain gap junctions and desmosomes. Gap junctions allow the depolarizing current produced by cations to flow from one cardiac muscle cell to the next, resulting in the coordinated contraction of the entire heart. Desmosomes, on the other hand, act as anchors, holding the ends of cardiac muscle fibres together to prevent them from pulling apart during contractions.
Cardiac muscle cells are mononucleate, meaning they have a single nucleus located in the central region of the cell. This is in contrast to skeletal muscle fibres, which are multinucleate and responsible for voluntary movements. Cardiac muscle cells also possess many mitochondria and myoglobin, as ATP is primarily produced through aerobic metabolism.
The contractions of cardiac muscle cells are involuntary, spontaneous, and rhythmic. They are similar to skeletal muscle contractions but with some differences. Cardiac muscle cells are capable of inducing electrical impulses, leading to action potentials and coordinated contractions that enable the heart to function as a pump.
The unique structure of cardiac muscle cells, with their branching and cylindrical shape, extensive branching, and intercalated discs, facilitates the highly coordinated contractions necessary for pumping blood into the vessels of the circulatory system.
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Cardiac muscle cells are striated
Cardiac muscle cells, also called cardiomyocytes, are striated. They are located in the walls of the heart and are under involuntary control. They are tubular structures composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells.
Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. The thick myofilaments contain the protein myosin, while the thin myofilaments contain the protein actin. The myofilaments slide past each other as the muscle contracts and relaxes, producing the formation of "cross-bridges," which cause the contraction of the heart and the generation of force. This process is activated by the release of calcium from the sarcoplasmic reticulum during the delivery of an action potential to the muscle, in a process called excitation-contraction coupling.
The outside of the cardiomyocyte is surrounded by a plasma membrane called the sarcolemma, which acts as a barrier between extracellular and intracellular contents. Invaginations of the sarcolemma, called T-tubules, contain numerous proteins that allow for the exchange of ions with extracellular fluid surrounding the cell. At the Z-line of the cardiomyocyte, T-tubules run adjacent to enlarged areas of the sarcoplasmic reticulum, known as terminal cisternae. Neighbouring cardiomyocytes are joined together at their ends by intercalated discs, creating a syncytium of cardiac cells.
Cardiac muscle cells are mononucleate, meaning they typically contain only one centrally-located nucleus. This contrasts with skeletal muscle cells, which often contain multiple nuclei. Cardiac muscle cells are specialized for the rapid, rhythmic, and spontaneous contraction and relaxation necessary for pumping blood throughout the cardiovascular system.
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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 and are responsible for the ability of the heart to pump blood. The cardiac muscle is the most hard-working muscle in the body, contracting and relaxing 60-100 times per minute from intrauterine life until death, which can be 80-90 years later.
Cardiac muscle cells are mononucleate striated cells, with fast, rhythmic, spontaneous contractions. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. The cardiac muscle in the wall of the left ventricle has a particularly heavy workload, having to force oxygenated arterial blood around the body. The cardiac muscle comprises the bulk of the heart wall proper, with small amounts found in the superior vena cava and pulmonary vein.
The cardiac muscle is not under conscious control; it has an automaticity center that is influenced by the autonomic nervous system. The contraction and relaxation of the cardiac muscle are similar to that of the skeletal muscles but with some differences. Cardiac muscle cells are joined in a network of fibers and are connected by gap junctions, which facilitate the conduction of electrical impulses through the cardiac muscle network.
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). These pacemaker cells are distributed throughout the heart and are responsible for several functions, including the ability to spontaneously generate and send out electrical impulses.
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Frequently asked questions
No, cardiac muscles are mononucleate or uninucleate, meaning they have one nucleus per cell, but can sometimes have two nuclei.
Mononucleated muscles are those that have one nucleus per cell. Smooth muscle cells and cardiac muscle cells are mononucleated.
Multinucleated muscles are those that have multiple nuclei per cell. Skeletal muscles are multinucleated.
