Intercalated discs or lines of Eberth are microscopic identifying features of

cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle th ...

. Cardiac muscle consists of individual heart muscle cells (

cardiomyocytes Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

) connected by intercalated discs to work as a single functional

syncytium A syncytium (; plural syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleu ...

. By contrast, skeletal muscle consists of

multinucleate Multinucleate cells (also known as multinucleated or polynuclear cells) are eukaryotic cells that have more than one nucleus per cell, i.e., multiple nuclei share one common cytoplasm. Mitosis in multinucleate cells can occur either in a coordina ...

d muscle fibers and exhibits no intercalated discs. Intercalated discs support synchronized contraction of cardiac tissue. They occur at the Z line of the

sarcomere A sarcomere (Greek σάρξ ''sarx'' "flesh", μέρος ''meros'' "part") is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called mus ...

and can be visualized easily when observing a longitudinal section of the tissue.

Structure

Intercalated discs are complex structures that connect adjacent

cardiac muscle cell Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

s. The three types of cell junction recognised as making up an intercalated disc are

desmosome A desmosome (; "binding body"), also known as a macula adherens (plural: maculae adherentes) (Latin for ''adhering spot''), is a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adh ...

s, fascia adherens junctions, and gap junctions. *

Fascia adherens In anatomy for cardiac muscle, fascia adherens are ribbon-like structures that stabilize non-epithelial tissue. They are similar in function and structure to the zonula adherens or adherens junction of epithelial cells. It is a broad intercellular ...

are anchoring sites for

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ov ...

, and connect to the closest sarcomere. *

Desmosome A desmosome (; "binding body"), also known as a macula adherens (plural: maculae adherentes) (Latin for ''adhering spot''), is a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adh ...

s prevent separation during contraction by binding intermediate filaments, anchoring the cell membrane to the intermediate filament network, joining the cells together. *

Gap junctions Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regula ...

connect the cytoplasms of neighboring cells electrically allowing cardiac action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...

of the heart muscle. All of these junctions work together as a single unit called the area composita.

Clinical significance

Mutations in the intercalated disc gene are responsible for various

cardiomyopathies Cardiomyopathy is a group of diseases that affect the heart muscle. Early on there may be few or no symptoms. As the disease worsens, shortness of breath, feeling tired, and swelling of the legs may occur, due to the onset of heart failure. A ...

that can lead to heart failure. Histopathology of ruptured intercalated discs

Ruptured intercalated discs, when seen on histopathology, have two main causes: * Microtome sectioning, thereby being a

visual artifact Visual artifacts (also artefacts) are anomalies apparent during visual representation as in digital graphics and other forms of imagery, especially photography and microscopy. In digital graphics * Image quality factors, different types of vi ...

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in: *Forceful myocardial contraction, in turn mainly caused by

ventricular fibrillation Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the ventricles of the heart quiver. It is due to disorganized electrical activity. Ventricular fibrillation results in cardiac arrest with loss of consciousness and n ...

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in: or

electrical injury Electrical injury is a physiological reaction caused by electric current passing through the body. The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or produce a ...

. Additional signs indicating forceful myocardial contraction are: *Alternating bundles of hypercontracted myocytes with hyperdistended ones. *Square-shaped myocardiocyte nuclei. *Hyperdistended myocardiocytes with detached sarcomeres, and in proximity of hypercontracted myocardiocytes. File:Cardiac myofiberbreak-up -- very high mag.jpg, Square-shaped nuclei, indicating forceful myocardial contraction.

References

External links

* — "Ultrastructure of the Cell: cardiac muscle, intercalated disk " {{Authority control Cardiac anatomy