Cardiovascular/Heart (ch.18) Pt2

What initiates the heartbeat and coordinates heart contractions?

Intrinsic cardiac conduction system, including pacemaker cells, gap junctions, and autorhythmic cells.

What is the function of the Sinoatrial (SA) node?

Acts as the pacemaker of the heart, generating impulses at a rate of about 75 beats per minute.

How does the Atrioventricular (AV) node affect heart contractions?

Delays impulses by approximately 0.1 seconds to allow for atrial contraction before ventricular contraction.

What happens during the depolarization phase of a cardiac action potential?

Calcium channels open, allowing a massive influx of Ca2+, leading to the rising phase of the action potential.

What is the role of gap junctions in the heart?

They allow electrical impulses to pass quickly between cardiac muscle cells, promoting coordinated contractions.

What is an arrhythmia?

An irregular heart rhythm that results from defects in the intrinsic conduction system.

What is defibrillation used for?

To interrupt chaotic twitching of the heart, allowing it to restart regular, normal depolarizations.

What does an Electrocardiogram (ECG) measure?

It records the electrical activity of the heart and can detect various cardiac abnormalities.

What does a prolonged Q-T interval signify?

It indicates a repolarization abnormality that increases the risk of ventricular arrhythmias.

What are the major components of an ECG and their meanings?

P wave: atrial depolarization; QRS complex: ventricular depolarization; T wave: ventricular repolarization.

What is the significance of the cardiac muscle's longer action potential duration compared to skeletal muscle?

It ensures sustained contraction for efficient blood ejection and prevents tetanic contractions.

What may result from a defective SA node?

An ectopic focus may take over pacing, leading to an abnormal heart rhythm.

What is the purpose of the cardioacceleratory center?

It sends sympathetic signals to increase the heart rate and force of contractions.

What does the atrioventricular bundle (bundle of His) do?

It is the only electrical connection between the atria and ventricles.

What is extrasystole?

A premature contraction triggered by an ectopic focus that causes a delayed next impulse.

What can elevated or depressed S-T segments indicate?

They may indicate cardiac ischemia.

One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a DECREASED efflux of what ion?

Potassium (K+) ions

Repolarization of an autorhythmic cell is due to the opening of which channels?

Voltage-gated potassium channels

What does the QRS complex represent in the ECG wave tracing?

ventricular depolarization

Contraction of the atria results from which wave of depolarization in ECG tracing?

P wave