Block 3 - Conduction and Rhythm Flashcards
What is intrinsic control?
Heart depolarizes and contracts w/o NS stimulation
What is extrinsic control
Rhythm can be altered by ANS
What factors coordinate heart beat?
- Gap junctions
- Intrinsic cardiac conduction system
What are the components of intrinsic cardiac conduction system?
- Network of non contractile (auto rhythmic cells)
- Initiate and distribute impulses → coordinated depolarization and contraction of heart
Describe the activity of pacemaker cells (action potential)?
- Pacemaker potential: Repolarization closes K+ channels and opens slow Na+ channels → ion imbalance →
- Depolarization:
Ca2+ channels open → huge influx → rising phase of action potential - Repolarization
K+ channels open → efflux of K+
Unstable resting membrane potential is caused by?
Opening of slow Na+ channels
At threshold, ___ channels open?
Ca2+
Explosive Ca2+ influx produces ___
Rising phase of action potential
Describe the action potential initiation by contractile cardiomyocytes?
Describe the sequence of excitation?
SA node → Av node → V bundles → right and left bundle branches → Purkinje fibers (subendocardial conducting network)
What is the purpose of the SA node?
- Pacemaker of heart in right atrial wall
- Depolarizes faster than the rest of the heart
SA node impulse? Inherent rate?
75x/min (sinus rhythm)
100X/min
How does AV node differ from SA?
- Delays impulse 0.1 sec
- Smaller fibers → fewer gap junctions
- Atrial contraction
Inherent rate of AV nodes?
50x/min without SA node input
What is the function of AV bundles?
Only electrical connection between atria and ventricles
(not connected by gap junctions)
What is the function of the right and left bundle branches?
Carry impulses toward apex of heart
What is the function of subendocardial conducting network?
- Complete pathway through inter ventricular septum into apex and ventricular wall
- More elaborate on left side of heart
Intrinsic rate of Punjenke fibers?
Depolarizes 30X/min in absence of AV node input
What happens after Pujenke fibers?
Ventricular contraction from apex toward atria
Describe the overal intrinsic cardiac conduction system during action potential?
Identify the action potential shapes?
What occurs during extrinsic innervation of the heart?
ANS via cardiac centers in medulla oblongata
1. Sympathetic → Increased rate and force
2. Parasympathetic → Decrease rate
3. Cardioacceleratory center → stimulate SA, AV, muscles, and coronary arteries
4. Cardioinhibitory center → inhibits SA and AV via vague nerves
What are the components of ECG?
- P wave – depolarization SA node → atria
- QRS complex - ventricular depolarization and atrial repolarization
- T wave - ventricular repolarization
What occurs during the PR interval?
Beginning of atrial excitation to beginning of ventricular excitation
What occurs during the ST segment?
Entire ventricular myocardium depolarized
What occurs during the QT segment?
Beginning of ventricular depolarization through ventricular repolarization