Action Potential Types

Fast- and Slow Response Action Potentials

Slow response: Ionic currents Why slow response?

Fast response: Atria Slow response: Ventricles, Purkinje Fibers Fast response: Atria Slow response: Ventricles, Purkinje Fibers. SAN, AVN High dv/dt: >200 V/s High conduction velocity: 1-4 m/s Specific drug sensitivity: sodium channel blockers – (lidocaine) and tetrodotoxin Low dv/dt: < 20 V/s Low conduction velocity: 0.02-0.05 m/s Specific drug sensitivity: calcium channel blockers – nifedipine, verapamil Spontaneous phase 4 depolarization

Automaticity Pacemakers hierarchy: SAN,AVN, Purkinje fibers

Why are fibers of the conducting system automatic? Membrane potential of SA nodal cells

Pacemaker Frequency - Mechanisms