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Vocabulary flashcards for myocardial muscle tissue physiology, covering cardiac myocyte structure, function, electrical properties, and the cardiac cycle.

Cardiac Myocytes

Relatively short muscle cells with branches that connect to one another, unlike skeletal muscle cells.

Intercalated Discs

The junctions where one cardiac muscle cell connects to a neighboring cell, characterized by desmosomes and gap junctions.

Desmosomes

Protein junction molecules within intercalated discs that resist physical stress and prevent cells from tearing apart.

Gap Junctions

Protein junction molecules within intercalated discs that allow cells to share nutrients, wastes, and electric current (action potentials).

Striations

Stripes resulting from the spatial arrangement of myofilaments (muscle proteins arranged into myofibrils) in both cardiac and skeletal muscle tissue.

Myofilaments

Muscle proteins (actin and myosin) arranged into bundles called myofibrils.

Mitochondria

Organelles that are more abundant in cardiac cells compared to skeletal cells due to the continuous activity and high energy demand of cardiac muscle.

Myocardium

Two subtypes of cardiac muscle cells: contractile cells and conductive cells.

Contractile Cells

The majority of cells in the myocardium (over 99%) whose function is to generate muscular force during the cardiac cycle to push blood around.

Conductive Cells

Less than 1% of the cells in the myocardium whose function is to rapidly conduct electric current from one point to another within the heart.

Sinoatrial Node (SA Node)

A cluster of connecting conductive cells in the wall of the right atrium that normally generates current first and fires action potentials first.

Atrioventricular Node (AV Node)

A node at the junction between the atria and the ventricles that is stimulated to fire action potentials when current flows through the atria.

Fibrous Skeleton of the Heart

A layer of thick fibrous connective tissue that blocks electric signals between the atria and ventricles.

AV Bundle and Bundle Branches

Connecting branches of conductive cells that pass electric current down the middle of the interventricular septum.

Purkinje Fibers

Additional conductive cell branches near the apex of the heart that shoot up the lateral edges of the ventricular walls.

AV Nodal Delay

A brief pause that occurs before the AV node passes on electric current to ensure the timing of the mechanical events of the cardiac cycle is correct.

Autorhythmic and Pacemaker Cells

Alternate names for conductive cells, indicating their ability to generate current on their own without external stimulation.

Biological Pacemaker

The part of the heart that fires an action potential first, setting the pace for heart contraction; normally the SA node.

Pacemaker Potential

The slow depolarization that occurs in conductive cells, allowing them to self-depolarize and set the pace for the heart's contraction.

Excitation-Contraction Coupling

The process by which firing an action potential stimulates contraction in contractile cells, involving calcium release and binding to troponin.

Troponin

A regulatory protein on the thin filament that is activated by calcium binding, causing a change in shape and movement of tropomyosin.

Tropomyosin

A regulatory protein of the thin filament that is moved away from binding sites on actin for myosin by activated troponin.

Plateau Phase

A phase in the contractile myocyte action potential characterized by a more horizontal part of the curve, resulting from the balance of calcium and potassium ion movement, which prolongs the action potential and prevents muscle twitch summation.