Intercalated discs or lines of Eberth are microscopic identifying features of

cardiac muscle 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. It is an involuntary, striated muscle that constitutes the main tissue of the wall o ...

. Cardiac muscle consists of individual heart muscle cells (

cardiomyocytes 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. It is an involuntary, striated muscle that constitutes the main tissue of the wall of ...

) connected by intercalated discs to work as a single functional

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

. By contrast, skeletal muscle consists of

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

d muscle fibers and exhibits no intercalated discs. Intercalated discs support synchronized contraction of cardiac tissue in a wave-like pattern so that the heart can work like a pump. 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 striated muscle, Skeletal muscles are composed of tubular ...

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 or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the Heart#Wa ...

s. The three types of

cell junction Cell junctions or junctional complexes are a class of cellular structures consisting of multiprotein complexes that provide contact or adhesion between neighboring Cell (biology), cells or between a cell and the extracellular matrix in animals. Th ...

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 ad ...

s, fascia adherens junctions, and

gap junction Gap junctions are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such small molecules, substrates, and metabolites. Gap junctions were first described as ''close appositions'' alongside tight ...

s. *

Fascia adherens In the anatomy of the cardiac muscle, a fascia adherens also known as an adhesive strip is one of the ribbon-like structures that stabilize non-epithelial tissue. They are similar in function and structure to the zonula adherens or adherens junctio ...

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 ...

, 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 ad ...

s prevent separation during contraction by binding

intermediate filament Intermediate filaments (IFs) are cytoskeleton, cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate ''Branchiostoma' ...

s, anchoring the cell membrane to the intermediate filament network, joining the cells together. *

Gap junctions Gap junctions are Membrane channel, membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such small molecules, substrates, and metabolites. Gap junctions were first described as ''close appositions' ...

connect the cytoplasms of neighboring cells electrically allowing

cardiac action potential Unlike the action potential in skeletal muscle cells, the cardiac action potential is not initiated by nervous activity. Instead, it arises from a group of specialized cells known as pacemaker cells, that have automatic action potential generati ...

s 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 (biology), cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolar ...

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 primary diseases of 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. An ...

that can lead to

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to Cardiac cycle, fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF ...

Histopathology of ruptured intercalated discs

Ruptured intercalated discs, when seen on

histopathology Histopathology (compound of three Greek words: 'tissue', 'suffering', and '' -logia'' 'study of') is the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopatholog ...

, have two main causes: *

Microtome A microtome (from the Greek ''mikros'', meaning "small", and ''temnein'', meaning "to cut") is a cutting tool used to produce extremely thin slices of material known as ''sections'', with the process being termed microsectioning. Important in sc ...

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 v ...

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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 Ventricle (heart), ventricles of the heart Fibrillation, quiver. It is due to disorganized electrical conduction system of the heart, electrical activity. Ventricula ...

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in: or

electrical injury An electrical injury (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs on direct contact with an electric current. The injury depends on the density of the current, tissue resistance an ...

. 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