Electrical Conduction of the Heart

A set of vocabulary flashcards covering the physiology of cardiac muscle, the components of the heart's electrical conduction system, and the mechanics of cardiac action potentials.

Action potential

A rapid sequence of changes in the voltage or electricity across a cell membrane, also described as an electrical impulse.

Resting membrane potential (RMP)

The voltage across a given membrane of a cell during its resting stage, approximately $-70\,mV$ on average, without any electrical impulse stimulating the cell.

Depolarisation

A change within a cell where the electrical charge distribution across the membrane shifts, resulting in a less negative charge inside the cell.

Repolarisation

A change in membrane potential that returns it to its negative value just after the depolarisation phase of an action potential occurs.

Autorhythmicity

A unique property of some heart cells to show rhythmic electrical activity without being driven by external stimulation.

Cardiac conduction system

A specialized network of muscle fibers in the heart that provide a path for cardiac excitation to spread throughout the heart as a wave.

Threshold

The specific voltage level (e.g., $-40\,mV$ in nodal cells) that must be reached for an action potential to be triggered.

Sodium-potassium pump

A protein channel that maintains ion balances by pumping sodium one way and potassium in the opposite direction across the cell membrane.

Nodal cells

The approximately $1\%$ of cardiac cells that are self-excitable (autorhythmic) and set the rhythm of the heart.

Contractile cells

The $99\%$ of cardiac cells responsible for the mechanical work of moving blood through the heart.

Refractory period

The interval of time (about $250\,ms$ in cardiac muscle) during which a second action potential cannot be initiated regardless of the stimulus size.

Intercalated disks

Connections between cardiac muscle fibers that contain gap junctions and desmosomes to allow the heart to contract as a single coordinated unit.

Sinoatrial (SA) node

Located in the superior posterolateral wall of the right atrium, it acts as the natural pacemaker of the heart.

Atrioventricular (AV) node

A collection of nodal cells where the electrical impulse is delayed for about $0.12\,s$ to allow atria to empty blood into the ventricles.

Internodal pathways

Small band fibers that transmit electrical impulses from the SA node to the AV node.

Atrioventricular (AV) bundle

Also known as the bundle of His, it provides the electrical connection between the atria and the ventricles.

Bundle branches

The left and right pathways that travel down the interventricular septum to start ventricular contraction.

Purkinje fibers

Highly branched conductive fibers that transmit action potentials into the ventricular mass to stimulate strong, simultaneous contraction.

Pacemaker potential

The slow depolarisation towards threshold ($0\,mV$ or $-40\,mV$) seen in nodal cells that lack a stable resting membrane potential.

L-type calcium channels

Slow, long-lasting calcium channels that allow calcium influx during the plateau phase of a contractile fiber's action potential.

Plateau phase

A phase of maintained depolarisation in contractile cells caused by the inflow of calcium and a slow efflux of potassium.

T-tubules (transverse tubules)

Structures that penetrate the muscle fiber to allow electrical impulses to travel deep into the cell and trigger calcium release.

Troponin

A regulatory protein that calcium binds to inside the contractile fiber to allow actin and myosin filaments to slide and develop tension.

Tetanus

A state of repeated contraction without relaxation; this cannot occur in cardiac muscle because the refractory period lasts longer than the contraction.