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The heart is the only organ in the human body that is also a muscle. This muscle, also known as cardiac muscle or myocardium, is a unique type of striated muscle tissue that is responsible for the contractile function of the cardiac pump. It is composed of cardiomyocytes, which are cardiac muscle cells with distinctive cellular and physiological features. These cells are joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The myocardium forms the thick middle layer of the heart wall, with the endocardium as the inner layer and the pericardium as the outer layer.
| Characteristics | Values |
|---|---|
| Common Name | Cardiac Muscle |
| Other Names | Heart Muscle, Myocardium |
| Type | Involuntary, Striated Muscle |
| Composition | Cardiac Muscle Cells (Cardiomyocytes/Cardiac Rhabdomyocytes), Intercalated Discs, Collagen Fibers, Connective Tissue, Fibroblast Cells, Leukocytes, Adipocyte Rests |
| Function | Contraction and Relaxation, Pumping Blood Through Cardiovascular System |
| Location | Middle Layer of Heart Wall |
| Blood Supply | Coronary Circulation, Coronary Arteries |
| Related Diseases/Conditions | Cardiomyopathies, Ischemic Conditions, Angina, Myocardial Infarction, Hypertrophy, Myocarditis |
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What You'll Learn
- Cardiac muscle, also called myocardium, is the middle layer of the heart wall
- It is composed of cardiac muscle cells, also known as cardiomyocytes or cardiac rhabdomyocytes
- Cardiac muscle cells are connected by intercalated discs, allowing them to contract together to pump blood
- Cardiomyocytes contain many mitochondria to produce large amounts of adenosine triphosphate (ATP) and myoglobin to store oxygen
- Diseases of the heart muscle, known as cardiomyopathies, include ischemic conditions like angina and myocardial infarction
Cardiac muscle, also called myocardium, is the middle layer of the heart wall
The heart is the only organ that is also a muscle. It is made of a special type of muscle tissue called cardiac muscle, also known as myocardium or heart muscle. This muscle is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle.
Cardiac muscle, or myocardium, is the middle layer of the heart wall. It is a thick layer of involuntary, striated muscle that constitutes the main tissue of the wall of the heart. It is composed of individual cardiac muscle cells, or cardiomyocytes, joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. This matrix plays a pivotal role in the three-dimensional organisation and mechanical performance of the heart. The myocardial thickness is related to the pressure present in each chamber; the atria are thin-walled, and the ventricles are thicker.
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. This includes longitudinally (becoming shorter from apex to base), radially (becoming narrower from side to side), and with a twisting motion (similar to wringing out a wet cloth) to squeeze the maximum amount of blood out of the heart with each heartbeat.
Cardiac muscle cells are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Cardiomyocytes contain many mitochondria to produce large amounts of adenosine triphosphate (ATP) and myoglobin to store oxygen to meet the demands of muscle contraction. A distinct feature of cardiac muscle fibres is that they have their own auto-rhythmicity. Unlike smooth or skeletal muscle, which require neural input for contraction, cardiac fibres have their own pacemaker cells like the sinoatrial (SA) node that spontaneously depolarises.
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It is composed of cardiac muscle cells, also known as cardiomyocytes or cardiac rhabdomyocytes
The heart is the only organ that is also a muscle. It is composed of cardiac muscle cells, also known as cardiomyocytes or cardiac rhabdomyocytes. These cells are unique to the heart and are not found anywhere else in the body. They are responsible for the contractile function of the cardiac pump, allowing the heart to beat and pump blood throughout the body.
Cardiac muscle cells are interconnected through intercalated discs, which facilitate the transfer of electrical stimulation from one cell to the next. This allows the cells to contract in a synchronised manner, creating a wave of contractions that result in the heartbeat. Cardiomyocytes have distinct cellular and physiological features, including a high number of mitochondria and extensive capillary networks. These features enable the production of large amounts of adenosine triphosphate (ATP) and the storage of oxygen to meet the demands of muscle contraction.
Cardiac muscle, also called myocardium, forms the thick middle layer of the heart wall. It is composed of sheets of cardiac muscle cells arranged in overlapping spiral patterns. These sheets wrap around the left ventricle, contracting in a coordinated manner to allow the ventricle to squeeze in multiple directions simultaneously. This complex arrangement enables the heart to squeeze the maximum amount of blood out of the heart with each heartbeat.
The myocardial thickness varies depending on the pressure present in each chamber, with the atria having thin walls and the ventricles having thicker walls. The thickness of the left ventricular free wall is approximately three times that of the right ventricle due to the higher pressure in the systemic circulation compared to the pulmonary circuit. The myocardial thickness is also influenced by physiological changes, such as chronic hypertension, which can lead to compensatory cardiomyocyte hypertrophy and an increase in ventricular muscle wall thickness.
Cardiomyocytes, or cardiac muscle cells, play a crucial role in maintaining the contractile function of the heart. They work in conjunction with pacemaker cells, which set the rhythm of the heart contractions. The pacemaker cells are weakly contractile and are connected to the neighbouring contractile cardiomyocytes through gap junctions. Together, these specialised cells ensure the continuous beating of the heart and the effective pumping of blood throughout the body.
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Cardiac muscle cells are connected by intercalated discs, allowing them to contract together to pump blood
The human body is made up of more than 600 muscles, each serving a specific function. One such muscle is the cardiac muscle, also known as the myocardium or heart muscle, which is one of the three types of vertebrate muscle tissues. The cardiac muscle forms the thick middle layer of the heart wall, with the outer layer being the pericardium and the inner layer being the endocardium.
Cardiac muscle cells, also known as cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are rectangular, branching cells that contain a large number of mitochondria to produce adenosine triphosphate (ATP) and myoglobin to store oxygen to meet the demands of muscle contraction. Cardiac muscle cells have their own auto-rhythmicity and are joined by intercalated discs, which are small connections that allow the cells to contract together in a fluid, synchronized fashion.
The intercalated discs contain gap junctions that transfer the stimulation to contract from one cardiac muscle cell to the next. This synchronized contraction of the cardiac muscle cells is essential for the heart to function as a pump. The cardiac muscle contracts in a similar manner to skeletal muscle, but with some key differences. For instance, the contraction of cardiac muscle is triggered by electrical stimulation in the form of a cardiac action potential, which causes the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum.
The rise in calcium levels causes the cell's myofilaments to slide past each other, leading to muscle contraction. This process is known as excitation-contraction coupling. The force generated by the contraction of the cardiac muscle propels blood through the cardiovascular system. Additionally, the powerful contraction of the cardiac muscle contributes to cardiac lymph flow, which is primarily driven by a passive pumping mechanism.
In summary, cardiac muscle cells are connected by intercalated discs, allowing them to contract together in a synchronized manner to pump blood throughout the body. This unique ability of the cardiac muscle is essential for maintaining adequate tissue and organ perfusion, making it a vital component of the human body.
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Cardiomyocytes contain many mitochondria to produce large amounts of adenosine triphosphate (ATP) and myoglobin to store oxygen
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. The myocardium forms a thick middle layer of the heart wall, with blood supplied via the coronary circulation. It is composed of individual cardiac muscle cells, known as cardiomyocytes, which are joined by intercalated discs.
Cardiomyocytes are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. These cells are responsible for the contractile function of the cardiac pump, allowing the heart to generate force to maintain adequate tissue and organ perfusion throughout the body. Contracting heart muscle uses a lot of energy, and therefore requires a constant flow of blood to provide oxygen and nutrients.
Cardiomyocytes contain many mitochondria, which are the powerhouse organelles of cells. They participate in ATP generation, calcium homeostasis, oxidative stress response, and apoptosis. Mitochondria are important generators of energy, providing ATP through oxidative phosphorylation. During embryonic and fetal development, mitochondria respond to metabolic changes and transition from small, fragmented mitochondria to large organelles capable of producing enough ATP to support the contractile function of the heart. This maturation process of mitochondria is likely not merely a response to overall cardiomyocyte maturation; rather, mitochondria may be mediators of the molecular processes triggering maturation of cardiomyocytes.
Mitochondria in mature cardiomyocytes are large, occupying about 1/3 of the cardiomyocyte volume, and are organised between myofibrils (intermyofibrillar), beneath the sarcolemma (subsarcolemmal) or near the nucleus (perinuclear). In adult cardiac cells, spheroid mitochondria are densely confined among myofibrils to ensure quick and efficient energy fluxes. This type of arrangement limits the movement of mitochondria.
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Diseases of the heart muscle, known as cardiomyopathies, include ischemic conditions like angina and myocardial infarction
The cardiac muscle, also called the myocardium or heart muscle, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that forms the thick middle layer of the heart wall, known as the myocardium. The myocardium is responsible for the contractile function of the cardiac pump, allowing the heart to pump blood effectively.
Diseases of the heart muscle, known as cardiomyopathies, are of major importance. Cardiomyopathy is a disease that affects the myocardium, causing the heart to stiffen, enlarge or thicken, and can result in scar tissue formation. As a result, the heart's pumping ability is compromised, leading to reduced blood flow to the body. Cardiomyopathy can be caused by various factors, including genetic mutations, coronary artery disease, autoimmune diseases, infections, heart inflammation, and high cholesterol.
One of the most common ischemic conditions related to cardiomyopathy is myocardial ischemia, which occurs when there is a lack of blood supply to the myocardium due to a partial or complete blockage of the coronary arteries. This obstruction is often caused by a buildup of plaques, mainly composed of cholesterol, leading to atherosclerosis. Myocardial ischemia can result in angina pectoris, characterised by chest pain or discomfort, and can progress to a heart attack (myocardial infarction) if left untreated. Myocardial infarction occurs when the blockage becomes severe, causing irreversible damage to the heart muscle.
Angina can be stable, usually relieved by rest or medication, or unstable, occurring at any time, even during relaxation or sleep. Treatment for myocardial ischemia focuses on improving blood flow to the myocardium and may include medications such as nitroglycerin for angina relief, beta-blockers, and procedures like angioplasty to open blocked arteries or bypass surgery. Leading a heart-healthy lifestyle is crucial in treating and preventing myocardial ischemia, as it helps maintain strong and elastic arteries, promoting maximum blood flow.
In summary, diseases of the heart muscle, or cardiomyopathies, include ischemic conditions like angina and myocardial infarction, which arise from restricted blood supply to the myocardium. Effective treatments are available for cardiomyopathies, and early diagnosis and intervention are essential to prevent complications and improve heart health.
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Frequently asked questions
Cardiac muscle, also known as myocardium or heart muscle, is one of three types of vertebrate muscle tissues. It is involuntary and striated, and constitutes the middle layer of the heart wall.
Cardiac muscle is:
- Striated
- Involuntary
- Contractile
- Fibrous
- Rhythmic
Cardiac muscle is responsible for the contractile function of the cardiac pump. It contracts and relaxes to pump blood through the cardiovascular system.
