Heart Physiology, Cardiac Conduction, and Regulation Flashcards

Comprehensive vocabulary flashcards covering heart conduction, electrocardiograms, arrhythmias, the cardiac cycle, cardiac output, and autonomic regulation of heart rate.

Automaticity

The unique trait of specialized pacemaker cells in the heart that enables them to generate action potentials and stimulate contraction independently.

Rhythmicity

The characteristic property of the heart to beat at regular, rhythmic intervals.

Sinoatrial (SA) node

The primary pacemaker of the heart, located in the wall of the right atrium just below the opening of the superior vena cava; fires at an intrinsic rate of $60$ to $80$\,\text{beats per minute}.

Atrioventricular (AV) node

A node located near the right AV valve at the lower end of the interatrial septum that slows the cardiac impulse to allow the atria to contract and ventricles to fill; fires at $40$ to $60$\,\text{beats per minute}.

Purkinje fibers

Conducting fibers that distribute electrical impulses throughout the myocardium of both ventricles to cause almost simultaneous contraction; fire at an intrinsic rate of $20$ to $40$\,\text{beats per minute}.

Ectopic pacemaker

Any pacemaker in the heart other than the SA node, such as the AV node or Purkinje fibers, that initiates impulses if the SA node fails.

Bundle of His

Also called the atrioventricular (AV) bundle; the conducting structure where the impulse picks up speed after exiting the AV node, before dividing into right and left bundle branches.

Electrocardiogram (ECG)

A composite recording of all action potentials produced by nodal and myocardial cells during a heartbeat, detected by electrodes placed on the body surface.

Normal sinus rhythm

An ECG tracing that appears normal, indicating that the cardiac electrical impulse originates in the SA node.

Arrhythmia

An irregular heartbeat resulting from damage to the conduction pathway or from an ectopic focus in the myocardium.

P wave

The ECG wave representing atrial depolarization, occurring immediately before the atria contract.

PR interval

The time required on an ECG for the cardiac impulse to travel from the atria to the ventricles.

QRS complex

The ECG complex representing ventricular depolarization as electrical impulses spread through the ventricles.

ST segment

The ECG segment representing the end of ventricular depolarization and the start of ventricular repolarization.

T wave

The ECG wave representing ventricular repolarization.

Atrial flutter

An arrhythmia caused by a rapidly firing ectopic focus in the atria, causing atrial contractions of $200$ to $400$\,\text{times per minute}.

Atrial fibrillation

An arrhythmia where the atria quiver rather than contract properly, causing blood to pool in the atria and raising the risk of blood clots.

Premature ventricular contractions (PVCs)

Extra heartbeats resulting from the firing of an ectopic focus in the ventricles; may occur singly or in bursts.

Ventricular fibrillation

A life-threatening medical emergency where disorganized electrical signals cause the ventricles to quiver without pumping blood, leading to plummeting cardiac output.

Electrical cardioversion

A procedure in which a timed electrical jolt timed to the R wave is delivered to the heart to depolarize excitable tissue and reset normal sinus rhythm.

Defibrillation

Emergency administration of a strong electrical jolt across the heart via large electrodes to depolarize the entire myocardium and allow the SA node to resume normal sinus rhythm.

Cardiac cycle

The complete sequence of events during a single heartbeat, consisting of systole (contraction) and diastole (relaxation).

Atrial kick

The active contraction of the atria late in the ventricular filling stage that supplies the ventricles with the final $30\%$ of their blood volume.

First heart sound (S1)

The louder and longer heart sound ("lub") caused by the sudden closure of the AV valves as ventricular pressure rises at the start of ventricular contraction.

Second heart sound (S2)

The softer and sharper heart sound ("dub") caused by blood rebounding against the closed semilunar valves during ventricular relaxation.

Isovolumetric contraction

A brief period at the start of ventricular systole when all heart valves are closed and ventricular pressure rises steeply while blood volume stays constant.

Residual volume

The amount of blood that remains inside the ventricles at the end of the ejection period.

Isovolumetric ventricular relaxation

The phase at the end of ventricular ejection following semilunar valve closure but before AV valve opening, where ventricular pressure drops sharply without a volume change.

Cardiac output (CO)

The total volume of blood pumped by the heart in $1$\,\text{minute}, calculated as $\text{CO} = \text{HR} \times \text{SV}$.

Stroke volume (SV)

The volume of blood ejected by a ventricle with each individual heartbeat, averaging about $70$\,\text{mL} at rest.

Bradycardia

A persistent resting heart rate slower than $60$\,\text{beats per minute}.

Tachycardia

A persistent resting heart rate greater than $100$\,\text{beats per minute}.

Cardiac center

A sensory integration center located within the medulla of the brain containing acceleratory and inhibitory centers to adjust heart rate via the autonomic nervous system.

Acceleratory center

A center within the cardiac medulla stimulated by stress or exercise that sends impulses along the sympathetic nervous system to increase heart rate and force of contraction.

Inhibitory center

A center in the cardiac medulla stimulated by factors like rising blood pressure that sends signals over the parasympathetic nervous system to slow heart rate.

Cardiac nerves

Nerves of the sympathetic nervous system that release norepinephrine to the SA node, AV node, and myocardium to increase heart rate and force.

Vagus nerve

The parasympathetic nerve that releases acetylcholine to the SA and AV nodes to slow heart rate.

Factors Affecting Heart Rate Flowchart

Diagram showing how the medulla's cardiac center regulates heart rate through acceleratory (sympathetic/norepinephrine) and inhibitory (parasympathetic/vagus nerve/acetylcholine) pathways.