1. Action Potential Types

2. Fast- and Slow Response Action Potentials

3. Slow response: Ionic currents
Why slow response?

4. 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: m/s
Specific drug sensitivity: calcium channel blockers –
nifedipine, verapamil
Spontaneous phase 4 depolarization

5. Automaticity
Pacemakers hierarchy:
SAN,AVN, Purkinje fibers

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

7. Pacemaker Frequency - Mechanisms