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Cardiac Muscle Tissue

Introduction to the Cardiac Muscle Tissue:

image descriptionCardiac muscle cells (cardiocytes or cardiac myocytes) make up the myocardium portion of the heart wall.

Unlabelled image of the cardiac muscle cells
Labelled image of the cardiac muscle cell of fiber
The cardiac muscle cell or fiber.
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They are relatively short, image descriptionbranched fibers that measure approximately 10 to 10 micrometers in diameter and 50 to 100 micrometers in length.

Unlabelled image of the cardiac muscle cells
Labelled image of branched fiber of a cardiac muscle cell
The cardiac muscle tissue consists of short branched fibers.
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Typically each cardiac myocyte contains a single image descriptionnucleus, which is centrally positioned.

Unlabelled image of the cardiac muscle cells
Labelled image of the nucleus of a cardiac myocyte
The nucleus of a cardiac myocyte.
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Thick and thin myofilaments are present and organized into myofibrils.

Their overlapping arrangements creates alternating dark (A) and light (I) bands or image descriptionstriations, similar to those seen in skeletal muscle tissue.

Unlabelled image of the cardiac muscle cells
Labelled image of the striations on a cardiac muscle fiber
The striations of the myofibrils.
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Sarcoplasmic reticulum tubules surround the myofibrils. However, they are not well organised and do not have terminal cisternae. T-tubules are also present but run along the Z-discs (instead of the myofilament overlap zones).

The mitochondria in the cardiac myocytes are large and numerous. They supply the ATP for repeated contractions of the heart.

Unlike other types of muscle tissue, cardiac myocytes are joined end to end by image descriptionintercalated discs.

Unlabelled image of the cardiac muscle cells
Labelled image of an intercalated disc
Myocytes joined end to end by intercalated discs.
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These complex, highly convoluted image descriptioncouplings contain both anchoring junctions and electrical junctions.

Magnified view of an intercalated disc animation slide 1
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Magnified view of an intercalated disc animation slide 12
Magnified view of an intercalated disc.

Forming the anchoring juntions are fascia adherens and desmosomes, which attach the adjacent myocytes.

The electrical junctions are composed of connexion protein channels, which usually occur in clusters referred to as image descriptiongap junctions.

Magnified view of an intercalated disc animation slide 12
Labelled image of the gap junction of the intercalated disc
The gap junction of an intercalated disc.
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image descriptionConnexion proteins span the distance between adjacent plasma membranes and ions can travel through the channel pores.

Exchange of ions at a gap junction animation slide 1
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Exchange of ions at a gap junction animation slide 3
Exchange of ions at a gap junction animation slide 4
Exchange of ions at a gap junction animation slide 5
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Exchange of ions at a gap junction animation slide 7
Exchange of ions at a gap junction animation slide 8
Exchange of ions at a gap junction animation slide 9
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Exchange of ions at a gap junction animation slide 11
Exchange of ions at a gap junction animation slide 12
Exchange of ions at a gap junction animation slide 13
Ions travelling through the channel pores of connexion proteins.

The ion movement allows action potentials to pass directly from cell to cell. This property makes the entire myocardium act like a single cell (orĀ funtional syncytium).

image descriptionMicrograph of the cardiac muscle tissue.

Micrograph of cardiac muscle cells animation slide 1
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Micrograph of cardiac muscle cells animation slide 8
Micrograph of cardiac muscle cells animation slide 9
Micrograph of the cardiac muscle tissue.

Test yourself:

The cardiac muscle tissue: [image descriptionShow/image descriptionHide answers]

Test yourself image for the cardiac muscle tissue with answers hidden
Test yourself image for the cardiac muscle tissue with answers shown; cardiac muscle fiber, nucleus, intercalated disc, mitochondrion, myofibril, intercalated disc, fiber branch, striations, gap junction
Review the cardiac muscle tissue and test yourself.
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Test yourself:

Connexion proteins: [image descriptionShow/image descriptionHide answers]

Test yourself image for the gap junction with answers hidden
Test yourself image for the gap junction with answers shown; myocyte, connexion protein, plasma membrane
Review the connexion proteins and test yourself.
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Test yourself:

Micrograph of cardiac muscle tissue [image descriptionShow/image descriptionHide answers]

Test yourself image for the micrograph of cardiac muscle tissue with answers hidden
Test yourself image for the micrograph of cardiac muscle tissue with answers shown; central nucleus, branched fiber, red blood cells, intecalated disc, striated myocyte
Review the micrograph of the cardiac muscle tissue and test yourself.
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