11. Cardiac Electrophysiology

Question 1

What are the 4 ion channels in the heart?

Answer 1

Inward: Funny Na/K, Fast Na, Slow L-type Ca
Outward: K+

Question 2

What is the resting potential of the SAN?

Answer 2

-55mV

Question 3

Describe what happens in the SAN

Answer 3

Na+/K+  leak in, cell depolarises to -40
-40 causes opening of slow l-type ca channels
Ca/Na exchanger: 1 Ca out for 3 Na in
Ca channels close after 200msec
K+ opens, K leaves the cell
Repolarises back to -55

Question 4

What is the resting potential in ventricular muscle cells?

Answer 4

-90mV

Question 5

What is the refractory period?

Answer 5

Time when the cell is not able to respond again