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Cardiac muscle tissue, also known as myocardium, is a structurally and functionally unique subtype of muscle tissue located only in the heart. It forms the bulk of the heart, with the heart wall consisting of a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium. The cardiac muscle is made up of contractile myocytes that allow the heart to pump blood through the circulatory system.
| Characteristics | Values |
|---|---|
| Found in | The heart |
| Muscle type | One of three types of muscle tissues in the body |
| Muscle cells | Cylindrical, branched, slightly striated, and uninucleated |
| Muscle cell size | Smaller than skeletal muscles, averaging 10–20 mm in diameter and 50–100 mm in length |
| Contractibility | The ability to contract or shorten and generate force when stimulated by electrical signals |
| Rhythmicity | The ability to spontaneously depolarize and generate rhythmic impulses, independent of any external electrical signals from the nervous system |
| Excitability | The ability to respond to adequate stimuli or electrical impulses by generating an action potential |
| Conductivity | The ability to transmit cardiac impulses from one cell to another |
| Contraction | Similar to skeletal muscle but with some differences |
| Contraction type | Rhythmic and not under voluntary control |
| Pacemaker cells | A distinct type of cardiomyocyte that can generate action potentials and initiate contractions in cardiac muscles approximately 75 times per minute |
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What You'll Learn
Cardiac muscle tissue is found only in the heart
Cardiac muscle tissue, also known as myocardium, is a structurally and functionally unique subtype of muscle tissue located only in the heart. It is one of the three types of muscle tissue in the body, the other two being skeletal muscle tissue and smooth muscle tissue. The heart consists mostly of cardiac muscle cells, which form a highly branched cellular network in the heart.
The cardiac muscle is a specialised type of involuntary muscle tissue that makes up the bulk of the heart. Cardiac muscle cells, or cardiomyocytes, are elongated and spindle-shaped, with one to two centrally located nuclei. These cell fibres are arranged in a branching network and are joined by intercalated discs, which are junctions that allow these muscle cells to contract in synchronisation. The intercalated discs are small connections that join cardiac muscle cells to each other. When one cardiac muscle cell is stimulated to contract, a gap junction transfers the stimulation to the next cardiac cell. This allows the muscle to contract in a coordinated way and enables the heart to work as a pump.
The cardiac muscle is capable of strong, continuous, and rhythmic contractions that are automatically generated. The contractility can be altered by the autonomic nervous system and hormones. The contractile force developed by the cardiac muscle cells, as well as the frequency at which they are activated, are critical factors in determining the normal pumping performance of the heart. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium.
Cardiac muscle cells have a large number of myofibrils, which are specialised protein filaments that allow for efficient contraction. The myofibrils of cardiac muscle are arranged in a similar pattern to skeletal muscle, resulting in cross-striations. The regular organisation of myofibrils into sarcomeres gives cardiac muscle cells a striped or striated appearance when viewed through a microscope.
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It forms both the atria and ventricles of the heart
The heart is made up of four cavities, two atria and two ventricles. The atria are the upper chambers of the heart, and the ventricles are the lower chambers. The right atrium receives deoxygenated blood from the superior and inferior vena cavae, and from the coronary veins. The blood is pumped through the right atrioventricular orifice (guarded by the tricuspid valve) into the right ventricle. The right ventricle then pumps the blood through the pulmonary valve and into the lungs through the pulmonary arteries, where the blood receives oxygen.
The left atrium receives oxygenated blood from the four pulmonary veins and pumps it through the left atrioventricular orifice (guarded by the mitral valve) into the left ventricle. This is the last stop within the four chambers of the heart. From the left ventricle, blood passes into the aorta and enters the systemic circulation.
The heart contracts due to an electrical stimulus triggered by the conduction system. This stimulus begins in the sinus node, which is found where the superior vena cava enters the right atrium. This stimulus causes the atrium to contract. This stimulus then propagates to the ventricle through another structure called the atrioventricular node. The cardiac conduction system is made up of a series of cells that have the capacity to create this stimulus and determine heart rate.
Cardiac muscle tissue is one of the three types of muscle tissue in the body. It plays an important role in making the heart beat and keeping it pumping through involuntary movements. Cardiac muscle tissue forms the bulk of the heart. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium.
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It is structurally and functionally unique
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle tissue is only found in the heart and is responsible for the heart's contractility and pumping action.
Cardiac muscle cells 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 regular organisation of myofibrils into sarcomeres gives cardiac muscle cells a striped or striated appearance when viewed through a microscope, similar to skeletal muscle.
Cardiac muscle cells are the contracting cells that allow the heart to pump. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, working together 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.
The heart consists mostly of cardiac muscle cells, or myocardium. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium. The sheets of muscle that wrap around the left ventricle closest to the endocardium are oriented perpendicularly to those closest to the epicardium. When these sheets contract in a coordinated manner, they allow 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 cloth) to squeeze the maximum possible amount of blood out of the heart with each heartbeat.
The rhythmic contraction of cardiac muscle is regulated by the sinoatrial node of the heart, which serves as the heart's pacemaker. The pacemaker cells are located in the sinoatrial node, positioned on the wall of the right atrium, and in the atrioventricular node. These cells carry the impulses that are responsible for the beating of the heart.
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It has high metabolic, energy, and vascular demands
Cardiac muscle tissue is one of three types of muscle tissue in the body, the other two being skeletal muscle tissue and smooth muscle tissue. It is found only in the heart and forms the bulk of it.
Cardiac muscle tissue works to keep the heart pumping through involuntary movements. This is achieved through specialised cells called pacemaker cells, which set the rhythm of the heart contractions. The heart consists mostly of these cardiac muscle cells, also known as myocardium. The heart's pumping action is called contractility, and it is the basis for its ability to pump blood. The amount of blood pumped by the heart per minute, or the cardiac output, varies to meet the metabolic needs of the body's tissues, particularly the skeletal muscles, kidneys, brain, skin, liver, heart, and gastrointestinal tract.
The contraction of cardiac muscle cells requires a lot of energy. The bulk of the heart's energy for contraction is provided by the metabolism of oxidizable substrates. The final product of this oxidative metabolism in the mitochondria is ATP. The heart must continuously produce large amounts of ATP to sustain its contractile function. The heart converts chemical energy present in substrates and oxygen to mechanical energy (cardiac work) and heat (calories). An abrupt increase in cardiac work results in the recruitment of reserves in contractility and coronary flow.
The coronary arteries bring nutrients to the muscle cells, and veins and a capillary network take away waste products. Blood is brought to the myocardium by the coronary arteries, which originate from the aortic root and lie on the outer or epicardial surface of the heart.
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Cardiomyopathy is a disease that affects cardiac muscle tissue
Cardiac muscle tissue, or myocardium, is one of the three types of muscle tissue in the body. It is found only in the heart and is responsible for the heart's pumping action. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium.
Cardiomyopathy is a disease that affects the cardiac muscle tissue or myocardium. It is a heart muscle disease that causes the heart to lose its ability to pump blood effectively. Cardiomyopathy can make the heart stiffen, enlarge or thicken, and can also cause scar tissue. As a result, the heart cannot pump blood efficiently to the rest of the body. This can lead to other serious heart problems, including arrhythmias (irregular heartbeats), heart failure, heart valve disease, and even cardiac arrest.
There are several types of cardiomyopathy, including hypertrophic cardiomyopathy, dilated cardiomyopathy, ischemic cardiomyopathy, and restrictive cardiomyopathy. Hypertrophic cardiomyopathy occurs when the muscle of the left ventricle thickens, blocking blood flow to the rest of the body. It can also affect the heart's mitral valve, causing blood to leak backward. This is a rare, inherited disease that can affect both men and women of all ages. Dilated cardiomyopathy is when the heart becomes enlarged and cannot pump blood efficiently. Ischemic cardiomyopathy is caused by a restricted blood supply to the muscle, such as angina or myocardial infarction. Restrictive cardiomyopathy is not inherited but can be caused by other inherited diseases. It causes fatigue, swelling of the arms and legs, and trouble breathing.
Cardiomyopathy can be caused by various factors, including viral infections, genetic defects, and other underlying diseases or their treatments. Certain risk factors, such as a family history of cardiomyopathy, a personal history of heart attacks, high BMI, and long-term substance abuse, can also increase the likelihood of developing the disease. While there is no cure for cardiomyopathy, treatments are available to help manage symptoms and slow down the disease's progression. These include medications, lifestyle changes, and implanted devices. Regular exercise, in particular, can strengthen the cardiac muscle and reduce the risk of developing cardiomyopathy.
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Frequently asked questions
Cardiac muscles are found only in the heart.
Cardiac muscles are made of cardiac muscle cells, also called cardiomyocytes. These cells are surrounded by an extracellular matrix produced by supporting fibroblast cells.
Cardiac muscles work by contracting and relaxing. This process requires a constant supply of oxygen and nutrients to meet the energy demands of the muscles. 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 the blood into the pulmonary and systemic vessels.
Regular cardio exercise can help lower blood pressure, reduce heart rate, and make the heart pump more effectively. Exercise can also help reduce the risk of developing cardiomyopathy and make the heart work more efficiently.
