Snapshot A 60-year-old man presents to his cardiologist for a follow-up of newly diagnosed diastolic heart failure. He has a history of asthma and chronic obstructive lung disease. He reports that his pulmonologist does not want him to take β-blockers. However, his cardiologist wants to start him on a medication to slow the heart rate. He reassures the patient that this drug acts not on β-receptors but on a Ca2+ channel. (Verapamil) Introduction Ions responsible for the action potential of atria, ventricles, and Purkinje fibers are the same upstroke inward Na+ current plateau slow inward Ca2+ current via L-type voltage-gated Ca2+ channels a sustained period of depolarization allows for ventricular filling Ventricular Action Potential Resting membrane potential -85 mV resting membrane potential is maintained by inward rectifier K+ channels inward rectifier K+ channels open at rest and close with depolarization Phase 0, upstroke rapid depolarization caused by the opening of voltage-gated Na+ channels and inward Na+ current Na+ current depolarizes cell membrane, which closes inward rectifier K+ channels Phase 1, initial repolarization brief repolarization and net outward current inactivation gates on Na+ channels close Na+ current is decreased outward K+ current down an electrochemical gradient Phase 2, plateau stable, long period of depolarized membrane potential inward and outward current are equal, with no net current flow inward Ca2+ current (slow inward current) opened L-type Ca2+ channels blocked by Ca2+ channel blockers entry of Ca2+ also triggers the release of more Ca2+ from sarcoplasmic reticulum in the cell (Ca2+-induced Ca2+ release) outward K+ current driven by electrochemical driving force Phase 3, repolarization net outward current L-type voltage-gated Ca2+ channels close a decrease in inward Ca2+ current delayed rectifier K+ channels open completely and repolarize the membrane increase in outward K+ current inward rectifier K+ channels re-open Phase 4, resting membrane potential inward and outward currents are equal delayed rectifier K+ channels close inward rectifier K+ channels are fully open, resetting resting membrane potential at -85 mV
QUESTIONS 1 of 2 1 2 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.CV.13.119) A 48-year-old female comes into the ER with chest pain. An electrocardiogram (EKG) shows a heart beat of this individual in Image A. The QR segment best correlates with what part of the action potential of the ventricular myocyte shown in Image B? Tested Concept QID: 100635 FIGURES: A B Type & Select Correct Answer 1 Phase 0, which is primarily characterized by sodium influx 63% (22/35) 2 Phase 0, which is primarily characterized by potassium efflux 0% (0/35) 3 Phase 1, which is primarily characterized by potassium and chloride efflux 3% (1/35) 4 Phase 1, which is primarily characterized by calcium efflux 17% (6/35) 5 Phase 3, which is primarily characterized by potassium efflux 11% (4/35) M 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review tested concept
All Videos (1) Login to View Community Videos Login to View Community Videos Atria and Ventricular Contraction Cardiovascular - Myocardial Action Potential D 2/15/2015 111 views 5.0 (4)