The Electrical Highway
What structure is the heart’s natural pacemaker?
SA node
Which ion rushes into the cell during depolarization?
Sodium (Na⁺)
What property allows pacemaker cells to generate impulses without stimulation?
Automaticity
What does the PR interval represent?
Time from atrial depolarization to ventricular depolarization
How many seconds does one small box on ECG paper represent?
0.04 seconds
Which node delays the electrical impulse?
AV node
Which ion leaves the cell during repolarization?
Potassium (K⁺)
What property allows cardiac cells to respond to an electrical stimulus?
Excitability
What does the QRS complex represent?
Ventricular depolarization
How many seconds does one large box represent?
0.20 seconds
What structure carries the impulse from the AV node into the ventricles?
Bundle of His
What EKG wave represents atrial depolarization?
P wave
What property allows electrical impulses to travel from cell to cell?
Conductivity
What does the QT interval represent?
Total ventricular activity (depolarization + repolarization)
How many large boxes equal one full second?
Five large boxes
Which node slows the electrical impulse just long enough to allow the ventricles to fill?
AV node
Why is the QRS complex larger than the P wave?
The ventricles have more muscle mass.
What property allows cardiac cells to shorten and create a heartbeat?
Contractility
What does a prolonged PR interval indicate?
Slowed conduction through the AV node
If the PR interval measures 5 small boxes, what is the PR interval duration?
0.20 seconds
What part of the conduction system splits into right and left pathways?
Bundle branches
What happens to the T wave when potassium levels are abnormal?
It changes shape (peaked, flat, or inverted).
Which cardiac cells have the fastest rate of automaticity?
SA node cells
What does a widened QRS complex indicate?
Ventricular depolarization is taking longer than normal
If the QRS complex spans 3 small boxes, is it normal or wide?
3 small boxes = 0.12 seconds → wide