Cardiovascular Physiology 9

Question 1

What are the two types of action potential in the heart?

Answer 1

• Fast response action potential

* Slow response action potential

Question 2

Where are fast response action potential found?

Answer 2

• Contractile myocytes in the atrial and ventricular myocardium
• Myocytes part of the heart’s conduction system (bundle of His, left and right bundle branches, purkinje fibers)

Question 3

Where are slow response action potentials found?

Answer 3

Sinoatrial node and the atrioventricular node

Question 4

What do the terms fast and slow refer to in the two types of action potential of the heart?

Answer 4

How quickly the membrane potential changes during the depolarization phase of the action potential

Question 5

What is the rate of depolarization in a fast action potential?

Answer 5

Fast

Question 6

What is the rate of depolarization in a slow action potential?

Answer 6

Slower rate of depolarization where the membrane potential takes more time to reach the new potential

Question 7

Why do the two types of heart action potentials have different rates of depolarization?

Answer 7

The different combinations of ions and ion channels in the depolarization phase

Question 8

What are the important ions in the cardiac cells?

Answer 8

Sodium, Potassium and Calcium

Question 9

What is the concentration of potassium inside and outside the cardiac cell?

Answer 9

There is a high concentration of potassium inside and a low concentration of potassium outside

Question 10

What is the concentration of sodium and calcium inside and outside of myocytes?

Answer 10

Sodium and calcium have high concentrations outside the cell and low concentrations inside the cell

Question 11

What are the phases of the Slow Action Potential?

Answer 11

• Pacemaker potential
• Depolarization
• Repolarization

Question 12

What is the resting potential like in a slow action potential?

Answer 12

Slow action potentials do not have a steady but instead undergo a slow depolarization to threshold

Question 13

What is the Pacemaker potential of a slow action potential?

Answer 13

The gradual increase of membrane potential

Question 14

What allows the muscles in the heart to generate action potentials without any external influences?

Answer 14

The slow depolarization of membrane potential

Question 15

What are the different phases of the slow action potential brought about by?

Answer 15

The changes in the permeability of the membrane to various ions

Question 16

How does potassium contribute to the pacemaker potential in slow action potentials?

Answer 16

During the pacemaker potential there is a progressive reduction in potassium permeability

Question 17

What is the reduction in potassium permeability in the slow action potential caused by?

Answer 17

The closing of the potassium channels due to the return of the membrane to the negative potential

Question 18

When do F-type channels in slow action potentials open?

Answer 18

At negative potentials

Question 19

What do the F-type channels conduct in the slow action potentials?

Answer 19

Mainly inward sodium current, but they are non specific

Question 20

What do T-type channels do in the pacemaker potential of slow action potential?

Answer 20

Allow calcium into the cell bringing the channel to threshold

Question 21

What are the three channels involved in the pacemaker potential?

Answer 21

• K+ channels
• F-type channels
• T-type channels

Question 22

What is depolarization in a Slow action potential brought about by?

Answer 22

L-type channels that allow an influx of calcium

Question 23

What do L-type channels do in a slow action potential?

Answer 23

Allow an influx of calcium during depolarization

Question 24

What causes the repolarization of the slow action potentials?

Answer 24

The closing of L-type channels and the opening of potassium channels allowing potassium to leave the cell

Question 25

What channels are involved in depolarization of slow action potentials and what do the channels do?

Answer 25

L-type channels that allow calcium into the cell slowly

Question 26

What channels are involved in Repolarization in slow action potentials and what do those channels do?

Answer 26

Potassium channels that allow potassium to leave the cell

Question 27

What are responsible for the depolarization phase of the slow action potential?

Answer 27

Calcium currents

Question 28

How does calcium affect the rate of slow action potentials?

Answer 28

Calcium move through the channel more slowing resulting in a slow increase in membrane potential

Question 29

What occurs with the channels during the pacemaker phase of slow action potentials?

Answer 29

* Potassium channels close when the cell is at a negative membrane potential stopping potassium flow leaving the cell * F-type channels open allows sodium to enter the cell * T-type channels open allowing calcium to enter the cell depolarizing the membrane

Question 30

What occurs during the depolarization phase of a slow action potential?

Answer 30

•L-type channels open allowing calcium to slowly enter the cell moving down its concentration gradient

Question 31

What occurs during the repolarization phase of a slow action potential?

Answer 31

* Potassium channels open allowing potassium to leave the cell * L-type calcium channels close inhibiting calcium to enter the cell

Question 32

What is the difference in pacemaker potential of the AV and SA node?

Answer 32

The pacemaker potential in the AV node rises more slowly to threshold than the SA node