Cardiac Phys --> Ventricular and Pacemaker APs Flashcards Preview

Step 1 > Cardiac Phys --> Ventricular and Pacemaker APs > Flashcards

Flashcards in Cardiac Phys --> Ventricular and Pacemaker APs Deck (15):

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

1. pacemaker spontaneously depolarize due to If channels
2. Ca, not Na causes the uptroke
3. 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

1. Ach
2. 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

1. SA node
2. AV node

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