Cardio8 Flashcards
Ventricular Action Potential Pacemaker Action Potential
Where else does the Ventricular action potential occur?
Bundle of His
Purkinje fibers
Describe Phase 0 of the Ventricular Action potential.
Rapid Upstroke
- V-G Na+ channels Open
Describe Phase 1 of the Ventricular Action potential.
Initial Repolarization
- Inactivation of V-G Na+ channel
- V-G K+ channels begin to Open
Describe Phase 2 of the Ventricular Action potential.
Plateu
- Ca++ INflux through V-G Ca++ channels Balance K+ EFflux
- Ca++ INflux triggers Ca++ release from Sarcoplasmic Reticulum & Myocyte contraction
Describe Phase 3 of the Ventricular Action potential.
Rapid Repolarization
- Massive K+ EFflux d/t opening of V-G slow K+ channels
- Closure of V-G Ca++
Describe Phase 4 of the Ventricular Action potential.
Resting Potential
- High K+ permeability through K+ channels
Cardiac nodal cells spontaneously depolarize during ________ resulting in Automaticity due to ___ channels.
Diastole
I(f) channels - “funny current”
*responsible for a slow, mixed Na+/K+ inward current
How are cardiac myocytes electrically coupled?
Gap Junctions
Where does the Pacemaker Action Potential occur?
SA & AV nodes
What phases are missing in the Pacemaker Action potential when compared to the Ventricular action potential?
Phases 1 & 2 – Plateau is absent
What happens in phase 0 of the pacemaker action potential?
Upstroke
- Opening of VG Ca++ channels
- Fast VG Na+ channels are Permanently INactivated because of the less negative resting voltage of these cells.
*Results in a slow conduction velocity that is used by the AV node to prolong transmission from the atria to ventricles
What does the slop of phase 4 in the pacemaker action potential determine?
Heart Rate
___________ DEcrease the rate of Diastolic depolarization, while __________ INcrease depolarization and heart rate.
ACh/adenosine - DEcrease HR
Catecholimines - INcrease HR
