13. Cardiac Action Potentials

Question 1

What three structures in the heart have pacemaker capability?

Answer 1

SA node

AV node

Pukinje fibers

Question 2

What is the resting membrane potential for a “normal” cardiac myocyte?

Answer 2

-95

Question 3

What is the resting membrane potential of an SA nodal myocyte?

Answer 3

-65

Question 4

Do ventricular myocytes or atrial myocytes have a shorter action potential?

Answer 4

Atrial myocytes

Question 5

What do K+(d) channels do?

Answer 5

They are the voltage gated potassium channels which open in phase 3

Question 6

How does acetylcholine slow the heart rate?

Answer 6

They affect the Kb channels and keep them open, slowing phase 0 in the SA node.

ALSO it slows down the funny Na channels elongating phase 4

Question 7

What channels close / open in phase 3 of the SA node?

Answer 7

Calcium channels close and Kb channels open.

Question 8

In what phase do K(a) channels open?

Answer 8

Phase 1

Question 9

Which phase is typically related to conductance velocity?

Answer 9

Phase 0

Question 10

What would a negative lusitropic effect cause?

Answer 10

Longer duration of the relaxation of cardiac muscles.

Question 11

What is the effect of a positive dromotropic effect?

Answer 11

Increased speed of contuction

Question 12

What nerve supplies parasympathetic innervation to the heart?

Answer 12

The Vagus nerve