Athena Vale
The heart is a hardworking muscle that beats thousands of times a day to keep us alive. It is made up of cardiac muscle tissue, also known as myocardium, which is one of three types of muscle tissues in the body, the others being skeletal and smooth muscle tissue. The myocardium forms the thick middle layer of the heart, sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The cardiac muscle is composed of individual cardiac muscle cells, or cardiomyocytes, which are joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix.
| Characteristics | Values |
|---|---|
| Name | Cardiac muscle |
| Other names | Heart muscle, myocardium |
| Type | Involuntary, striated muscle |
| Location | Middle layer of the heart |
| Function | Keeps the heart pumping and blood circulating throughout the body |
| Composition | Individual cardiac muscle cells (cardiomyocytes) joined by intercalated discs |
| Regulation | Electrical impulses from pacemaker cells |
| Energy source | Adenosine triphosphate (ATP) |
| Contraction mechanism | Excitation-contraction coupling, calcium-triggered calcium release |
| Relaxation mechanism | Outward flow of potassium ions |
| Diseases | Cardiomyopathies, ischemic conditions (angina, myocardial infarction) |
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What You'll Learn
- Cardiac muscle, or myocardium, is one of three types of muscle tissues in the body
- It forms the thick middle layer of the heart, between the outer pericardium and inner endocardium
- Cardiomyocytes are the individual cells that make up the cardiac muscle
- Pacemaker cells generate electrical impulses, controlling the heart rate and contractions
- Cardiac muscle contracts similarly to skeletal muscle, but with important differences
Cardiac muscle, or myocardium, is one of three types of muscle tissues in the body
The heart is a muscle that beats thousands of times a day to keep us alive. It is made of cardiac muscle, also known as myocardium. This forms the thick middle layer of the heart, sandwiched between the outer layer of the heart wall (the pericardium or epicardium) and the inner layer (the endocardium).
Cardiac muscle is one of three types of muscle tissues in the body. The other two types are skeletal muscle tissue and smooth muscle tissue. Cardiac muscle is involuntary, meaning it contracts and relaxes on its own without conscious input. This is in contrast to skeletal muscle, which we can control.
Cardiac muscle is made up of individual muscle cells called cardiomyocytes, which are surrounded by an extracellular matrix. Cardiomyocytes are the contractile myocytes of the cardiac muscle. They are connected to each other by intercalated discs, which contain gap junctions that allow for the propagation of electrical impulses from one cell to the next. This allows the muscle to contract in a coordinated manner.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments towards each other, causing the cell to shrink. This process uses a lot of energy, and therefore the myocardium requires a constant flow of blood to provide oxygen and nutrients.
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It forms the thick middle layer of the heart, between the outer pericardium and inner endocardium
The heart is a hardworking muscle that beats thousands of times a day to keep us alive. It is made up of cardiac muscle, also known as myocardium, which is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle.
Cardiac muscle forms the thick middle layer of the heart, between the outer pericardium and inner endocardium. This three-layered structure is known as the heart wall. The myocardium is surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium.
The myocardium 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. 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.
The inner endocardium lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels connected to the heart. It also separates the left and right atria and ventricles. The endocardium is important for maintaining the structural integrity of the heart.
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Cardiomyocytes are the individual cells that make up the cardiac muscle
The heart is composed of cardiac muscle, also called heart muscle or myocardium. It is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
The primary function of cardiomyocytes is to contract, which generates the pressure needed to pump blood through the circulatory system. The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments, the interactions between which form the basis of the sliding filament theory. The myofilaments slide past each other as the muscle contracts and relaxes, producing the formation of "cross-bridges," which cause contraction of the heart and generation of force.
Cardiomyocytes are striated, branched, contain many mitochondria, and are under involuntary control. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Gap junctions between adjacent cardiomyocytes allow for the propagation of coordinated action potentials from one cell to the next in a phenomenon known as electrical coupling. This allows cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
Cardiomyocytes have a very long lifespan compared to other cells in the body. In humans, cardiomyocytes lose the ability to divide at around 7 days after birth. However, studies have shown that cardiomyocytes renew at a low rate throughout an individual's life, with the annual turnover of cardiomyocytes decreasing with age.
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Pacemaker cells generate electrical impulses, controlling the heart rate and contractions
The heart is composed of cardiac muscle, also known as myocardium. This muscle is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. The myocardium forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
Cardiac muscle is made up of individual muscle cells called cardiomyocytes, which are surrounded by an extracellular matrix. Cardiomyocytes are the contractile cells of the heart. The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. The interaction between these filaments forms the basis of the sliding filament theory.
Pacemaker cells are a type of specialized cardiomyocyte that sets the rhythm of the heart contractions. They comprise the sinoatrial (SA) node, which is the primary pacemaker, and the atrioventricular (AV) node, which is the secondary pacemaker. These pacemaker cells generate electrical impulses, known as cardiac action potentials, which control the rate of contraction of the cardiac muscle, or the heart rate.
Pacemaker cells are unique in that they can spontaneously generate and send out electrical impulses without requiring stimulation to initiate their action. This autorhythmicity is due to "funny current" channels that allow sodium ions to leak continuously into the cell, slowly raising the membrane potential until a certain threshold is reached, causing depolarization of the cell. Calcium channels then open, allowing calcium ions to enter the cell and further raise the membrane potential. This process results in the contraction of the heart, which pumps blood around the body.
The SA node is the heart's natural pacemaker, and it controls the rate of contraction for the entire heart muscle because its cells have the quickest rate of spontaneous depolarization. The SA node is located on the wall of the right atrium, near the entrance of the superior vena cava. The AV node is located near the central area of the heart. The electrical impulses generated by the SA node pass down the electrical conduction system of the heart, depolarizing the other potential pacemaker cells at the AV node, which then contract and propagate electrical impulses throughout the heart.
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Cardiac muscle contracts similarly to skeletal muscle, but with important differences
The heart is a muscular organ that pumps blood into circulation by generating sufficient force. The muscular ventricular septum originates from the bottom of the ventricle, with a membranous septum forming shortly after, joining with the aortic-pulmonary septum as it twists down and fuses. The heart is made up of three layers: the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
Cardiac muscle, like skeletal muscle, is made up of sarcomeres that allow for contractility. However, unlike skeletal muscle, cardiac muscle contracts involuntarily. The individual cardiac muscle cell (cardiomyocyte) is a tubular structure 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. Thin myofilaments contain the protein actin, and thick myofilaments contain the protein myosin. The myofilaments slide past each other as the muscle contracts and relaxes.
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. This process is called excitation-contraction coupling. The rise in calcium causes the cell's myofilaments to slide past each other. The sliding of actin and myosin past each other produces the formation of “cross-bridges”, which causes contraction of the heart and generation of force.
Cardiac muscle fibres have their own autorhythmicity, which means they have their own pacemaker cells like the sinoatrial (SA) node that spontaneously depolarizes. These depolarizations occur at a consistent pace, but the pacemaker cells can also receive input from the autonomic nervous system to decrease or increase the heart rate depending on the body's requirements. In contrast, smooth and skeletal muscles require neural input for contraction.
Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
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Frequently asked questions
The heart is made of cardiac muscle tissue, also called myocardium.
Myocardium is a type of muscle tissue that forms the heart. It is one of three types of muscle tissues in the body, the others being skeletal and smooth muscle. It makes up the thick middle layer of the heart, between the outer layer of the heart wall (the pericardium or epicardium) and the inner layer (the endocardium).
The heart pumps blood through the circulatory system by contracting and releasing involuntarily. The heart's contractions are controlled by specialized cells called pacemaker cells. These cells generate electrical impulses, or action potentials, that tell cardiac muscle cells to contract and relax.
