Cardiovascular Physiology 10

Question 1

What is the difference between the resting potential of the fast type action potential (ventricular muscle cell action potential) and the SA node action potential?

Answer 1

The ventricular action potential has a flat resting potential

Question 2

What do the contractile cells of the heart need to bring them to threshold?

Answer 2

A stimulus

Question 3

What is the resting membrane of the muscle cell of the heart permeable to?

Answer 3

Potassium

Question 4

What is the resting potential near?

Answer 4

The resting potential of the potassium potential

Question 5

What causes the ventricular muscle cells to not be at resting potential?

Answer 5

Excitation by electrical activity propagated from adjacent cells through gap junctions

Question 6

What is the depolarizing phase of a ventricular muscle cell action potential due to?

Answer 6

The opening of fast voltage gated sodium channels

Question 7

What does the opening of voltage gated channels in the depolarization of a ventricular muscle cell do?

Answer 7

Allow sodium to rush into the cell down their electrochemical gradient

Question 8

What depolarizes the cell in a ventricular muscle cell action potential?

Answer 8

The opening of voltage gated sodium channels that allow sodium to enter the cell

Question 9

How is the permeability of potassium to the membrane affected during depolarization of a ventricular muscle cell action potential?

Answer 9

The permeability of the membrane to potassium decreases

Question 10

What happens once the ventricular muscle cell reaches +30mV?

Answer 10

The voltage gated sodium channels close and the notch occurs

Question 11

What is the Notch?

Answer 11

Following rapid depolarization, brief repolarization occurs in the ventricular muscle cells

Question 12

What is the notch caused by?

Answer 12

A special class of transient potassium channels that allows potassium to leave the cell

Question 13

What occurs after the notch?

Answer 13

The plateau

Question 14

What is the plateau?

Answer 14

The phase occurring after the notch in the ventricular muscle cell action potential where the membrane remains at a potential of 0mv

Question 15

What is the plateau due to?

Answer 15

•Voltage gated L-type calcium channels that allows calcium into the cell
•The slow opening of potassium channels that allow potassium to exit the cell
These both balance each other out

Question 16

What happens at the end of the Plateau?

Answer 16

• The L-type calcium channels close, stopping calcium from entering the cell
• The potassium channels continue to open allowing more potassium to exit the cell allowing for repolarization

Question 17

What is the depolarization phase of a ventricular muscle contraction due to?

Answer 17

The opening of fast voltage gated sodium channels

Question 18

What are the different potassium channels involved in the ventricular muscle cell action potential?

Answer 18

• Inward rectifying (iK1)
• Transient outward (ito)
• Delayed rectifiers (ikr and iks)

Question 19

Which channel is responsible for the notch phase?

Answer 19

The transient outward channel (ito)

Question 20

What occurs when the ito channel opens?

Answer 20

There is a small increase in the membrane permeability allowing potassium to leave the cell causing the notch

Question 21

Which channel is transient in the ventricular muscle cell action potential?

Answer 21

The ito transient outward channel

Question 22

What channels mediate the plateau phase of the ventricular muscle cell action potential?

Answer 22

• L-type calcium channels that allow calcium into the cell

* Delayed rectifiers (ikr and iks)

Question 23

What do the Delayed rectifying channels (ikr and iks) contribute to?

Answer 23

The plateau and the repolarization phases

Question 24

What does the inward rectifying channel (ik1) contribute to?

Answer 24

It sets the resting potential of the ventricular muscle cell