Cardiac Anatomy and Physiology Flashcards

The PR interval on the ECG reflects conduction through which structures?

Answer: Atria, AV node, and bundle of His

The PR interval encompasses atrial depolarization (P wave) plus the conduction delay through the AV node and bundle of His before ventricular activation begins.

Which cells in the heart have the property of automaticity, meaning they can spontaneously depolarize?

Answer: Pacemaker cells in the SA node, AV node, and His-Purkinje system

Automaticity — the ability to spontaneously depolarize — is possessed by pacemaker cells throughout the conduction system, with the SA node having the highest rate.

In the normal cardiac conduction sequence, what is the correct order of activation?

Answer: SA node → atria → AV node → bundle of His → bundle branches → Purkinje fibers → ventricles

Normal conduction proceeds from the SA node through the atria, pauses at the AV node, then travels via the His-Purkinje system to activate the ventricles.

Depolarization of cardiac muscle cells occurs primarily due to rapid influx of which ion?

Answer: Sodium (Na+)

Phase 0 of the cardiac action potential in non-pacemaker cells is characterized by rapid sodium influx through fast sodium channels, causing the steep upstroke of depolarization.

Which layer of the heart is responsible for the electrical-to-mechanical coupling that produces contraction?

Answer: Myocardium

The myocardium (middle muscular layer) is where electrical depolarization triggers calcium release and actin-myosin cross-bridge formation, producing mechanical contraction.

What does the ST segment on the ECG represent?

Answer: The period between ventricular depolarization and repolarization (plateau phase)

The ST segment corresponds to the plateau phase of the ventricular action potential when all ventricular cells are depolarized and no net electrical current flows.