A report on Cardiac muscle

3D rendering showing thick myocardium within the heart wall.

The swirling musculature of the heart ensures effective pumping of blood.

Intercalated discs are part of the cardiac muscle cell sarcolemma and they contain gap junctions and desmosomes.

One of three types of vertebrate muscle tissue, with the other two being skeletal muscle and smooth muscle.

- Cardiac muscle

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Cardiac cycle

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Performance of the human heart from the beginning of one heartbeat to the beginning of the next.

The cycle diagram depicts one heartbeat of the continuously repeating cardiac cycle, namely: ventricular diastole followed by ventricular systole, etc.—while coordinating with atrial systole followed by atrial diastole, etc. The cycle also correlates to key electrocardiogram tracings: the T wave (which indicates ventricular diastole); the P wave (atrial systole); and the QRS 'spikes' complex (ventricular systole)—all shown as color purple-in-black segments.

The Cardiac Cycle: Valve Positions, Blood Flow, and ECG

The parts of a QRS complex and adjacent deflections. Re the cardiac cycle, atrial systole begins at the P wave; ventricular systole begins at the Q deflection of the QRS complex.

$A Wiggers diagram illustrate events and details of the cardiac cycle with electrographic trace lines, which depict (vertical) changes in a parameter's value as time elapses left-to-right. The ventricular "Diastole", or relaxation, begins with "Isovolumic relaxation", then proceeds through three sub-stages of inflow, namely: "Rapid inflow", "Diastasis", and "Atrial systole". (During the "Diastole" period, the "Ventricular volume" increases (see red-line tracing), beginning after the vertical bar at "Aortic valve closes" and ending with the vertical bar at R in the QRS complex). + The ventricular "Systole", or contraction, begins with "Isovolumic contraction", i.e., with the vertical bar at "A -V valve closes"; it ends with completing the "Ejection" stage at the bar at "Aortic valve closes". During "Ejection" stage, the (red-line) tracing of "Ventricular volume" falls to its least amount (see ejection fraction) as the ventricles pump blood to the pulmonary arteries and to the aorta.$

Diastole (at right) normally refers to atria and ventricles at relaxation and expansion together—while refilling with blood returning to the heart. Systole (left) typically refers to ventricular systole, during which the ventricles are pumping (or ejecting) blood out of the heart through the aorta and the pulmonary veins.

CGI animated graphic of the human heart, sectioned, with motions and timing synced with the Wiggers diagram. The section shows: 1) the opened ventricles contracting once per heartbeat—that is, once per each cardiac cycle; 2) the (partly obscured) mitral valve of the left heart; 3) the tricuspid and pulmonary valves of the right heart—note these paired valves open and close oppositely. + (The aortic valve of the left heart is located below the pulmonary valve, and is completely obscured.) The (unsectioned) atria are seen above the ventricles.

Cardiac diastole: Both AV valves (tricuspid in the right heart (light-blue), mitral in the left heart (pink)) are open to enable blood to flow directly into both left and right ventricles, where it is collected for the next contraction.

Cardiac (ventricular) systole: Both AV valves (tricuspid in the right heart (light-blue), mitral in the left heart (pink)) are closed by back-pressure as the ventricles are contracted and their blood volumes are ejected through the newly-opened pulmonary valve (dark-blue arrow) and aortic valve (dark-red arrow) into the pulmonary trunk and aorta respectively.

The movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node.

Fascia adherens

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In anatomy for cardiac muscle, fascia adherens are ribbon-like structures that stabilize non-epithelial tissue.

Desmosome

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Cell structure specialized for cell-to-cell adhesion.

Desmosomes are one of the stronger cell-to-cell adhesion types and are found in tissue that experience intense mechanical stress, such as cardiac muscle tissue, bladder tissue, gastrointestinal mucosa, and epithelia.

Ventricular fibrillation

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Abnormal heart rhythm in which the ventricles of the heart quiver.

Fine ventricular fibrillation as seen on a rhythm strip

Ventricular fibrillation as seen in lead II

Micrograph showing myofibre break-up with squared nuclei, a morphologic correlate of ventricular fibrillation. H&E stain.

Histomorphologically, MFB is characterized by fractures of the cardiac myofibres perpendicular to their long axis, with squaring of the myofibre nuclei.

Gap junction

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Gap junctions are specialized intercellular connections between a multitude of animal cell-types.

Light microscope images do not allow us to see connexons themselves but do let us see the fluorescing dye injected into one cell moving into neighboring cells when gap junctions are known to be present

Annular gap junction cross section in TEM thin section. Gap junctions are usually linear rather than annular in TEM thin sections. It is thought that annular gap junctions result from engulfment by one of the two cells of the membrane plaque to form a vesicle within the cell. This example shows three layers to the junction structure. The membrane from each cell is the dark line with the whiter narrow gap between the two darkly stained membranes. In such electron micrographs there may appear to be up to 7 layers. Two lipid mono-layers in each membrane can stain as 3 layers plus one layer from the gap between them, similar to two stacked bread sandwiches with space between them

Gap junctions are particularly important in cardiac muscle: the signal to contract is passed efficiently through gap junctions, allowing the heart muscle cells to contract in unison.

This Holter monitor strip of a 5-year-old showing atrial tachycardia. This person was eventually diagnosed with tachycardia-induced cardiomyopathy.

Tachycardia-induced cardiomyopathy

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Tachycardia-induced cardiomyopathy (TIC) is a disease where prolonged tachycardia (a fast heart rate) or arrhythmia (an irregular heart rhythm) causes an impairment of the myocardium (heart muscle), which can result in heart failure.

Diad

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Structure in the cardiac myocyte located at the sarcomere Z-line.

This way, the wave of depolarization can be coupled to calcium-mediated cardiac muscle contraction via the sliding filament mechanism.

Calcium-induced calcium release

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Able to activate calcium release from intracellular Ca2+ stores (e.g., endoplasmic reticulum or sarcoplasmic reticulum).

Instead, CICR is thought to be crucial for excitation-contraction coupling in cardiac muscle.

Myocytolysis

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Myocytolysis refers to a state of significant damage to cardiac myocytes, muscle cells of the heart, caused by myocardial strain.

Calcium buffering

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Calcium buffering describes the processes which help stabilise the concentration of free calcium ions within cells, in a similar manner to how pH buffers maintain a stable concentration of hydrogen ions.

The regulation of free calcium is of particular importance in excitable cells like cardiomyocytes and neurons.