HUBS192 Lecture 9: The Excitable Heart

This set of flashcards covers the vocabulary regarding the electrical and contractile properties of the heart, the conduction pathway, and ECG interpretations based on Lecture 9 of HUBS192.

Electrical Cells

Cardiac cells that make up approximately $1\%$ of the heart, characterized by a "pale" striated appearance and low levels of actin and myosin.

Contractile Cells

Heart cells that make up $99\%$ of the heart, known as "working myocardial cells," which have a striated appearance and high levels of actin and myosin.

Intercalated disks

Structures that connect most cells of the heart and contain gap junctions to facilitate electrical signaling.

Gap junctions

Pores within intercalated disks with low resistance to ionic current, allowing current flow between adjacent cells.

Functional syncytium

A term describing how millions of cardiac cells behave as a single unit due to the presence of gap junctions.

Sinoatrial (SA) node

Known as the "pacemaker," this is where depolarization starts in the heart.

Atrioventricular (AV) node

A component of the conduction pathway that delays the electrical impulse to allow atria to complete contraction before the ventricles are excited.

Internodal bundles

The part of the conduction system that carries the electrical signal from the SA node to the AV node.

AV bundle

Also known as the atrioventricular bundle, it transmits the impulse from the AV node to the bundle branches.

Purkinje fibers

Specialized electrical cells that conduct the impulse upward through the ventricular walls to ensure coordinated contraction.

Depolarization

The electrical event that leads to the mechanical event of contraction in cardiac cells.

Repolarization

The electrical event that leads to the mechanical event of relaxation in cardiac cells.

Quiescence

The period in the cardiac cycle when the ventricles are fully repolarized and the heart is relaxed.

Electrocardiogram (ECG)

A recording of the electrical events (depolarization and repolarization) of the heart detected by electrodes.

Lead

A virtual line between two surface electrodes used in an ECG to detect differences in electrical activity.

P wave

The portion of the ECG trace that represents atrial depolarization initiated by the SA node.

QRS complex

The portion of the ECG trace representing the electrical event of ventricular depolarization, during which atrial repolarization also occurs.

T wave

The portion of the ECG trace representing ventricular repolarization, which begins at the apex.

Lubb

The first heart sound occurring during the cardiac cycle.

Dupp

The second heart sound occurring during the cardiac cycle.