1. Action potentials

2. Generation of action potentials

4. Na+ and K+ conductance at resting potentials

5. Refractory periods

6. Refractory periods and Na+ Channels

7. Refractory periods

8. Involvement of other Ions in Action potential

10. Cardiac Conduction
Generation of Action potential every 0.8 seconds, or 75 action potentials per minute at the SA node (Pacemaker of the heart) 10

11. 1 2 3 4

12. Cardiac Muscle Action Potential
Depolarization
Repolarization
Refractory period
Contraction
Membrane
potential (mV)
Repolarization due to closure
of Ca2+ channels and K+ outflow
when additional voltage-gated
K+ channels open
Rapid depolarization due to
Na+ inflow when voltage-gated
fast Na+ channels open
Plateau (maintained depolarization) due to Ca2+ inflow
when voltage-gated slow Ca2+ channels open and
K+ outflow when some K+ channels open
0.3 sec
+ 20
–20
–40
– 60
– 80
–100 2 1 3
Depolarization
Repolarization
Refractory period
Contraction
Membrane
potential (mV)
Rapid depolarization due to
Na+ inflow when voltage-gated
fast Na+ channels open
Plateau (maintained depolarization) due to Ca2+ inflow
when voltage-gated slow Ca2+ channels open and
K+ outflow when some K+ channels open
0.3 sec
+ 20
–20
–40
– 60
– 80
–100 2 1
Depolarization
Repolarization
Refractory period
Contraction
Membrane
potential (mV)
Rapid depolarization due to
Na+ inflow when voltage-gated
fast Na+ channels open
0.3 sec
+ 20
–20
–40
– 60
– 80
–100 1

15. Continuous Conduction in Unmyelinated axons