Cardiac Phys --> Ventricular and Pacemaker APs Flashcards
phase 0 in Vent AP; what happens, what channels are responsible
rapid upstroke–> due to opening of voltage gated Na channels
Phase 1 in Vent AP–> what happens, what channel/ ion resp
intitial repolarization–> opening of voltage-gated K channels (K flows out, decreasing the ptential)
*Na chann also inactivated
Phase 2 in vent. AP
Plateau phase–> Ca2+ channels open (Ca influx) and this balances K efflux
Phase 3 in vent AP
rapid depolarization–> due to massive K efflux; Ca channel closure, so depolarization is unopposed
Phase 4 in vent. AP
Resting potential–> is due to K+ permeability; potential is around -85 mV, reflection membrane permeability to primarily K
what electrically couples myocytes
gap junctions
Phase 4 of pacemaker AP; what is happening, what is responsible
Slow diastolic depolarization–> due to Na influx through If (funny) channels = once cell depolarizes, these open and allow a slowish leak of Na into cell
Phase 0 of pacemaker AP
Upstroke–> due to opening of voltage gated Ca channels and Ca influx
*upstroke in pacemaker is due to Ca, not Na influx like in most other cells of body, including myocytes
Phase 3 of pacemaker AP
repolarization–> inactivation of Ca channels and Activation of K channels = K efflux from cell causes repolarization to below threshold; once at a certain level, If channels open again and cycle starts over
3 key differences b/n ventricular Ap and pacemaker AP
- pacemaker spontaneously depolarize due to If channels
- Ca, not Na causes the uptroke
- Pacemakers have no plateau phase
What phase controls HR in pacemaker AP
Slope of the phase 4 (slow diastolic depolarization)
2 things that ↓ the slope of phase 4 in pacemaker
- Ach
- adenosine
- ↓ HR!
how does sympathetic stim (catecholamines) ↑ HR?
increase the chance that If channels are open, thus ↑ slope of phase 4 and ↑ HR
where do vent. APs occur (2)
ventricles, as well as bundle of His and Purkinje fibers
2 places pacemaker AP occurs
- SA node
2. AV node
