Cardiac Action Potentials

Question 1

What is the pacemaker of the cell?

Answer 1

SA node

Question 2

What other cells of the heart have pacemaker potential?

Answer 2

AV Node, Purkinje Fibers

Question 3

What is the path of electrical flow through the heart that creates our heart rate?

Answer 3

SA node, AV node, Bundle of His, Right and Left Bundle Branches, Purkinje Fibers

Question 4

What is unique about the AV node compared to the SA node?

Answer 4

It has a slower conduction velocity (SLOWER PHASE 4). This is to make sure that the atria have completed their job of filling the ventricles before the ventricles contract.

Question 5

What is occurring during phase 0 of an atrial/ventricular AP?

Answer 5

Depolarization Opening of (m) Na+ channels -note that these channels rapidly close after opening

Question 6

What is occurring during phase 1 of an atrial/ventricular AP?

Answer 6

Partial repolarization Closing of Na+ (m) channels Opening of K+ (a) channels

Question 7

What is happening during phase 2 of an atrial/ventricular AP?

Answer 7

Plateau L type Ca2+ channels open slowly and remain open thru phase 2 K+ (b) channels close slowly and remain closed thru phase 2

Question 8

What happens during phase 3 of an atrial/ventricular AP?

Answer 8

Repolarization Closing of Ca2+ gates Opening of K+ (b) gates Basically the opposite of phase 2

Question 9

What’s going on in phase 4? What ion is most permeable in this state and which channel contributes to this?

Answer 9

RMP K+ K+ (c) channels

Question 10

What is occurring in phase 4 during a SA/AV nodal AP?

Answer 10

Opening of f type Na+ channels Very slowly bringing RMP to threshold **Remember that phase 4 is slower (has smaller slope) in AV node compared to SA node***

Question 11

What’s going on during phase 0 of the SA/AV nodal AP?

Answer 11

Opening of slow T Ca2+ channels Closing of special K+ (b) channels

Question 12

What are K+ (b) channels sensitive to? What type of autonomic effect does this produce?

Answer 12

Acetylcholine, parasympathetic

Question 13

What’s happening during phase 3 of an AP in a SA/AV node?

Answer 13

Closing of T type Ca2+ channels Opening of special K+ (b) channels Basically the opposite of what is happening during phase 0

Question 14

What phases are NOT present in SA/AV nodal cells? Why?

Answer 14

Phases 1 and 2 Due to scarcity of traditional Na+ channels (remember we have the funny type Na+ channels during phase 4)

Question 15

What is the significance of having a phase 2 present in atrial and ventricular cell APs?

Answer 15

It elongates the time of atrial and ventricular contraction

Question 16

Why is electrical signaling in the heart not transmitted directly from the atria to the ventricles?

Answer 16

The heart itself is insulated via the fibroskeleton

Question 17

Define key characteristics of the absolute refractory period

Answer 17

No AP can be stimulated no matter how large the stimulus THE CELL IS SAYING ABSOLUTELY NOT Most of the Na+ (m) channels are closed

Question 18

Define key characteristics of an effective refractory period

Answer 18

CONDUCTED AP cannot be generated There is not enough inward current to conduct the next site.

Question 19

Define the key characteristics of a relative refractory period

Answer 19

Greater than normal stimulus required AP (if generated) has abnormal configuration and shortened plateau phase

Question 20

Supranormal period-what state are Na+ channels in?

Answer 20

Cell is MORE EXCITABLE Na+ inactivation gates are open again and Na+ channels are recovered

Question 21

Chonotropic

Answer 21

Changes heart rate

Question 22

What effect does a positive chonotropic effect have?

Answer 22

Increases HR (via increasing phase 4 -depolarization rate of the SA node)

Question 23

What effect does a negative chonotropic effect have?

Answer 23

Decreases HR (via decreasing phase 4-depolarization rate of the SA node)

Question 24

What type of effect does the sympathetic nervous system have on the heart? Using terminology covered in this leture

Answer 24

Positive chonotropic effect Via NE activating B1 receptors

Question 25

What type of effect does the parasympathetic nervous system have on the heart? Using the terminology covered in this lecture

Answer 25

Negative chonotropic effect Decreased activation of funny (f) Na+ channels Increases conductance of K+-Ach (Hyperpolarizes RMP)