Cardiac Action Potentials Flashcards
Pacemaker Cells
(Slow APs)
Pacemaker Potential
Unstable phase 4, Spontaneous Depolarization; Inward current caused by Na+ influx (IF), Inward Ca2+ current (ICa), Decreasing outward K+ current (IK)
AP upstroke
Caused by L-VGCC Ca2+ influx, This SLOW AP triggers the FAST AP seen in the heart (This interaction what allows coordinated heart beat!)
Repolarization
Increased K+ efflux (IK), Decreased Ca2+ Influx (ICa)
Contractile Cells
(Fast APs); order of phases: 4, 0, 1, 2, 3
Phase 4
Resting/resetting the RMP; Na+/K+ pump; RMP is -90mV
Phase 0
Depolarization; Influx of Na+ through FAST Na+ channels
Phase 1:
Early Rapid Repolarization;
FAST Na+ channels close, K+ efflux
Phase 2
Slow Repolarization (plateau phase); Purpose of plateau is to extend AP in cardiac muscle cell is as long as the time the heart is contracting to prevent tetanus, K+ efflux, influx of Ca2+ & Na+ (SLOW Na+ channels)
Phase 3
Final Rapid Repolarization; K+ efflux, Ca2+ & SLOW Na+ channels close
Normal Pacemakers
SA node; normally suppresses other “ectopic” foci
Electrical Conduction System Step 1
Action potentials originate in the SA node (pacemaker), and travel across the wall of the atrium to the AV node
Electrical Conduction System Step 2
Action potentials pass through the AV node and along the atrioventricular bundle, which extends from the AV node through the fibrous skeleton into the interventricular septum
Electrical Conduction System Step 3
The AV bundle divides into right and left bundle branches and action potentials descend to the apex of each ventricle along the bundle branches
Electrical Conduction System Step 4
Action potentials are carried by the Purkinje fibers from the bundle branches to the ventricular walls
