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Cardiac muscle, also known as myocardium or heart muscle, is one of the 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 is responsible for pumping blood into circulation by generating enough force and is composed of individual cardiac muscle cells or cardiomyocytes, joined by intercalated discs. Each cardiomyocyte contains a single, centrally located nucleus, confirming that cardiac muscle is indeed uninucleated.
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What You'll Learn
Cardiac muscle is uninucleate and involuntary
There are three types of muscle tissue in vertebrates: skeletal muscle, smooth muscle, and cardiac muscle. Cardiac muscle is found only in the heart and is made up of uninucleate cells. This means that each cardiac muscle cell contains a single nucleus. Cardiac muscle cells are also cylindrical in shape and branched, similar to skeletal muscle cells. However, unlike skeletal muscle cells, which are multinucleated, cardiac muscle cells did not fuse together during development. Instead, they are connected via intercalated discs and gap junctions, resulting in what is known as functional synchronism.
Being uninucleate is just one characteristic of cardiac muscle. It is also involuntary, meaning it is not under conscious control. This is in contrast to skeletal muscle, which is a type of voluntary muscle that responds to conscious commands. Smooth muscles are also involuntary and are found in the inner lining of organs and structures such as the stomach, oesophagus, intestines, and blood vessels.
The function of all muscles, including cardiac muscle, is to produce force and motion. Cardiac muscle is unique, however, in its ability to induce electrical impulses and give rise to action potentials due to its specialized excitable cells. This property is essential for the contraction and relaxation of the cardiac muscle, which is similar to that of skeletal muscle but with some distinct differences.
In summary, cardiac muscle is uninucleate, involuntary, cylindrical, and branched. It is found only in the heart and plays a crucial role in inducing electrical impulses and causing the contraction and relaxation necessary for cardiac function.
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Cardiac muscle is striated
Cardiac muscle, also known as myocardium or heart muscle, is one of three types of muscle tissues, the others being skeletal muscle and smooth muscle. It forms the thick middle layer of the heart wall, constituting the main tissue of the wall of the heart.
The cells of cardiac muscle, known as cardiomyocytes, are typically single cells with a single, centrally located nucleus. They are joined together by intercalated discs, forming long, branching cardiac muscle fibres that work together in a synchronised manner. This allows the ventricles to squeeze in multiple directions simultaneously, maximising the amount of blood pumped out of the heart with each heartbeat.
The contraction of cardiac muscle is involuntary and occurs without external stimulation. This intrinsic rhythm is set by specialised cardiomyocytes called pacemaker cells, which are distributed throughout the heart and carry impulses responsible for the heart's beating. These pacemaker cells are connected to neighbouring contractile cells via gap junctions, allowing for coordinated contractions.
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Cardiac muscle is found only in the heart
Cardiac muscle, also called myocardium, is one of three major categories of muscles found within the human body, the other two being smooth muscle and skeletal muscle. It is the only type of muscle out of the three that is found in the heart.
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 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 myocardium, or cardiac muscle, makes up the thick middle layer of the heart.
Cardiac muscle is composed of individual cardiac muscle cells called cardiomyocytes, which are joined by intercalated discs. Cardiomyocytes are the contractile myocytes of the cardiac muscle and are surrounded by an extracellular matrix produced by supporting fibroblast cells. They are responsible for the contraction of the cardiac muscle, which generates the pressure needed to pump blood through the circulatory system. The contraction and relaxation of the cardiac muscle are similar to that of skeletal muscle but with some differences. The cardiac cells of the heart are specialized excitable cells that can induce electrical impulses and give rise to the action potential.
Cardiac muscle cells are uninucleate, 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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Cardiac muscle is made up of sarcomeres
Cardiac muscle cells, also called cardiomyocytes, are made up of sarcomeres. These are the fundamental structural and functional units of striated muscle, and they are directly responsible for most of the muscle's mechanical properties. Sarcomeres generate active or contractile forces and determine the passive or elastic properties of striated muscle. In the heart, mutations in sarcomeric proteins are responsible for the majority of genetically inherited cardiomyopathies.
Sarcomeres are composed of thick and thin filaments – myosin and actin, respectively, along with a titin that anchors the myosin to the Z-lines. The cardiac muscle cytoskeleton is complex, composed of diverse macromolecular assemblies and yet intricately organized to coordinate the network between the sarcomeres. The contractile proteins actin and myosin are organized by a network of specialized proteins that combine structural and signalling functions. The cytoskeleton represents the main structural scaffold essential in the regulation of mechanical resistance, morphological integrity, and cell shape, providing the uniform transmission of tension along myofibrils.
The sarcomere is defined as the region of myofilament structures between two Z-lines. The distance between Z-lines (i.e. sarcomere length) ranges from about 1.6 to 2.2 μ in human hearts. Changes in sarcomere length are an important mechanism by which the heart regulates its force of contraction. As a myocyte is stretched (as occurs with increased ventricular preload), the sarcomeres within the myofibrils are also stretched. With increased sarcomere length, there is an increase in the force of contraction (i.e., tension development by the muscle fibre).
The cardiac myocyte is a specialized striated muscle cell that is approximately 25 μ in diameter and about 100 μ in length. They form a branching network of cells that are connected by intercalated discs. The myocyte is composed of bundles of myofibrils that contain myofilaments. The myofibrils have distinct, repeating microanatomical units, termed sarcomeres, which represent the basic contractile units of the myocyte.
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Cardiac muscle cells are called cardiomyocytes
Cardiac muscle cells, also called cardiomyocytes, are striated, branched, contain many mitochondria, and are under involuntary control. They are found only in the heart, forming the contractile walls of the organ. The heart is made up of three layers—the pericardium, myocardium, and endocardium. The myocardium forms the bulk of the heart and is responsible for the contractility of the heart, and therefore the pumping action. The cardiac muscle must contract with enough force to supply blood to meet the metabolic demands of the entire body.
Cardiomyocytes are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, working to efficiently pump blood from the heart. If this coordination breaks down, the heart may not pump at all, as can occur during abnormal heart rhythms such as ventricular fibrillation.
Cardiomyocytes are linked to the basement membrane via specialised glycoproteins called integrins. Humans are born with a set number of heart muscle cells, which increase in size as the heart grows during childhood development. Evidence suggests that cardiomyocytes are slowly turned over during ageing, but less than 50% of the cardiomyocytes present at birth are replaced during a normal lifespan. During heart pressure overload, cardiomyocytes grow through concentric hypertrophy, resulting in heart wall thickening.
Cardiac muscle cells are roughly rectangular when viewed through a microscope and are joined at their ends by intercalated discs to form long fibres. Each cell contains myofibrils, 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 cardiac action potential triggers muscle contraction by increasing the concentration of calcium within the cytosol. The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling.
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Frequently asked questions
Yes, cardiac muscles are uninucleated.
Cardiac muscle cells are also called cardiomyocytes.
Cardiac muscles are branched and cylindrical in shape.
The cells in muscle tissue have the ability to shorten or contract to produce body movement.
G. Q: Are skeletal muscles uninucleated?
