Cardiac Ion Channels & Action Potentials

Question 1

What modulates the Sinoatrial Node? How fast does the SA node fire?

Answer 1

Modulated by ANS

~100/min

Question 2

Parasympathetic tone slows the SA node to _________ /min

Answer 2

60-80

Question 3

Both the AV node and SA node are capable of spontaneous activity. Which one “controls” the heart rate? What is this process called?

Answer 3

SA node action potentials control AV action potentials.

This is called “overdrive suppression.” SA node spontaneously depolarizes faster than AV node.

Question 4

In order for an action potential to propagate from the SA node to the Ventricles, it must first pass through_______

Answer 4

The AV node.

Question 5

How are Fast and Slow Action potentials different?

think of what a graph of each would look like

Answer 5

SLOW:

1. No steady resting potential.
2. Rising phase is slow.
3. No plateau

FAST

1. Longer Plateau phase (caused by Ca++ ions entering cell)
2. Steady diastolic potential.
3. Fast rising phase.

Question 6

Where are slow APs found?

Answer 6

1. SA node (pacemaker cells)

2. AV node

Question 7

Where are fast APs found?

Answer 7

Atrial Muscle,
Perkinje Muscle,
Ventricular Muscle.

Question 8

There are 5 phases in a fast cardiac action potential. Name them and what happens during each phase.

Test questions WILL come from these NC

Answer 8

Phase 0: Depolarization (Rising phase)
Phase 1: Partial Repolarization during plateau
Phase 2: Plateau
Phase 3: Repolarization
Phase 4: Steady Resting Potential

Question 9

What generates the depolarization in Phase 0 of a fast cardiac action potential?
TQ

Answer 9

Sodium influx (I-Na)

I stands for current

Question 10

What causes the plateau in Phase 2 of a fast cardiac action potential?
TQ

Answer 10

Calcium Influx (I- Ca-L)

Question 11

What causes the slight repolarization in Phase 1 of a fast cardiac action potential?
TQ

Answer 11

Potasium efflux via I-Kto channel

transient outward potassium current

Question 12

What causes the repolarization in Phase 3 of a fast cardiac action potential?
TQ

Answer 12

I-K Rapid and Slow channels (IKr and IKs) allow potassium to flow out.

This is known as the Delayed Rectifier Current

Question 13

What causes the stabilization in Phase 4 of a fast cardiac action potential?
TQ

Answer 13

Ik1

This is known as the Inward Rectifier Current

Question 14

What are the phases of a slow cardiac action potential?

TQ

Answer 14

Phase 0: Depolarization
Phase 3: Repolarization
Phase 4: Gradual depolarization (not steady)

Question 15

Phase 0 of the slow cardiac AP is produced by…

TQ

Answer 15

Calcium channels turning on and off again,

Question 16

Phase 3 of the slow cardiac AP is produced by…

TQ

Answer 16

Delayed Rectifier current (IKr and IKs)

Question 17

Phase 4 of the slow cardiac AP is produced by…TQ

Answer 17

Funny Current (If). Produced by hyperpolarization and causes the upward creep of the slow cardiac AP.

This is involved in pacemaking.