Electrical Activity of the Heart Flashcards
What are the key events in excitation-contraction coupling in cardiac muscle?
Action potential triggers depolarization.
Voltage-gated Ca²⁺ channels open, allowing Ca²⁺ influx.
Ca²⁺-induced Ca²⁺ release from the sarcoplasmic reticulum.
Ca²⁺ binds to troponin, enabling actin-myosin cross-bridge formation.
Contraction occurs (systole).
Ca²⁺ is pumped back into the sarcoplasmic reticulum and out of the cell.
Relaxation occurs (diastole).
How does the action potential in pacemaker tissue differ from non-pacemaker tissue?
Pacemaker cells (SA node): Have an unstable resting membrane potential due to funny (If) Na⁺ channels, leading to spontaneous depolarization. No true resting potential.
Non-pacemaker cells (ventricular muscle): Have a stable resting membrane potential and a plateau phase due to slow Ca²⁺ influx, allowing sustained contraction.
What is the sequence of electrical activity in the heart?
SA node generates an impulse (pacemaker).
Atrial depolarization spreads via internodal pathways.
AV node delays impulse, allowing ventricular filling.
Bundle of His conducts the impulse toward ventricles.
Right and left bundle branches transmit signals down the septum.
Purkinje fibers spread excitation, triggering ventricular contraction.
What does the P wave represent in an ECG?
Atrial depolarization (SA node activation and atrial contraction).
What does the PR interval represent in an ECG?
The delay at the AV node, allowing ventricular filling before contraction.
What does the QRS complex represent in an ECG?
Ventricular depolarization (ventricular contraction).
What does the T wave represent in an ECG?
Ventricular repolarization (relaxation phase).
What does the QT interval represent in an ECG?
The total time for ventricular depolarization and repolarization.
