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Cardiac muscle, also known as myocardium, is one of three major categories of muscles found within the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle cells are located in the walls of the heart and are responsible for the heart's contractility and rhythmicity of contraction. The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium.
| Characteristics | Values |
|---|---|
| Location | Walls of the heart |
| Appearance | Striated or striped |
| Control | Involuntary |
| Composition | Fibroblasts, smooth muscle cells, and cardiomyocytes |
| Function | Keep the heart pumping and blood circulating throughout the body |
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What You'll Learn
Cardiac muscle cells
Cardiac muscle, also known as myocardium, is one of three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle cells, or cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are located in the walls of the heart and are responsible for the heart's pumping action.
The contractile units in cardiac muscle cells are called sarcomeres, which are composed 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 is known as excitation-contraction coupling. Cardiac muscle cells also contain mitochondria, which convert oxygen and glucose into energy in the form of adenosine triphosphate (ATP), which powers the contraction.
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Intercalated discs
Cardiac muscle, also known as myocardium, is one of three major categories of muscles in the human body. It is composed of cardiac muscle cells, or cardiomyocytes, that are responsible for the highly coordinated actions that keep the heart pumping and blood circulating throughout the body.
Fascia adherens junctions are anchoring structures that connect the actin cytoskeleton of adjacent cells. Desmosomes are major cell adhesion junctions that anchor the cell membrane to the intermediate filament network. Gap junctions, on the other hand, provide a pathway for the passage of ions between cells, allowing action potentials to spread between cardiac cells and producing depolarization of the heart muscle.
Together, these three types of junctions work as a single unit, known as the area composita, to facilitate mechanical coupling and electrical communication between cardiac muscle cells. This coordination ensures that the heart contracts in a synchronised manner, efficiently pumping blood from the heart.
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Pacemaker cells
Cardiac muscle, also called the myocardium, is one of three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. The myocardium 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.
The heart has two main classifications of cells: cardiomyocytes and pacemaker cells. Pacemaker cells are a specialised type of cardiomyocyte that sets the rhythm of the heart contractions. They are only weakly contractile and are connected to neighbouring contractile cells via gap junctions.
The pacemaker cells in the SA node and AV node are smaller and conduct at a relatively slow rate between the cells. If the SA node is damaged or if the electrical conduction system of the heart has problems, a secondary pacemaker sets the pace. In some cases, an artificial pacemaker may be used to produce these impulses synthetically.
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Cardiomyopathies
Cardiac muscle, also known as myocardium, is one of three major categories of muscles in the human body. It is composed of cardiac muscle cells or cardiomyocytes, which are responsible for the heart's contractions. These cells work in a highly coordinated manner to pump blood and circulate it throughout the body.
There are several types of cardiomyopathies, including dilated cardiomyopathy, hypertrophic cardiomyopathy, restrictive cardiomyopathy, and arrhythmogenic cardiomyopathy. Dilated cardiomyopathy causes the lower chambers of the heart to become larger and weaker, affecting the heart's pumping ability. Hypertrophic cardiomyopathy leads to an enlarged and thicker heart muscle, which can interrupt blood flow out of the ventricles. Restrictive cardiomyopathy results in stiffened ventricle walls, preventing adequate filling of blood and reducing the heart's pumping capacity. Arrhythmogenic cardiomyopathy occurs when fatty or scarred tissue replaces normal muscle tissue in the right ventricle, causing irregular heartbeats.
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Cardiac muscle tissue
The heart wall has three layers: the inner endocardium, the outer epicardium or visceral pericardium, and a thick layer of myocardium between them. The myocardium is made up of sheets of cardiac muscle cells that wrap around the heart chambers, with the sheets closest to the endocardium oriented perpendicularly to those closest to the epicardium. This arrangement enables the ventricles to squeeze in multiple directions simultaneously, maximising the amount of blood pumped out with each heartbeat.
Cardiac muscle cells have a unique structure, appearing striated or striped under a microscope due to the alternating filaments of myosin and actin proteins. The thick filaments, composed of myosin, appear as dark stripes, while the thin, lighter filaments contain actin. During muscle contraction, the myosin and actin filaments slide past each other in a process called excitation-contraction coupling, resulting in the cell shrinking. This process is regulated by calcium ions released from the sarcoplasmic reticulum, the cell's internal calcium store.
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Frequently asked questions
Cardiac muscles are located in the heart.
Cardiac muscles are made up of sarcomeres, which are contractile units that allow for contractility.
Cardiac muscles appear striped or striated under a microscope.
Cardiac muscles work through involuntary movements, which are controlled by specialised cells called pacemaker cells.
