Lecture 9: Cardiac APs

Question 1

What is the circle of Willis?

Answer 1

Arteries on the brains inferior surface organised into a circle

Question 2

What % of CO is used for kidneys?

Answer 2

20-25%

Kidneys are 0.5% of body weight - 50 fold over perfused vol/weight

Question 3

Where is ACE made?

Answer 3

Kidney

Question 4

Where is renin made?

Answer 4

Kidney

Question 5

What % of adult body mass is skeletal muscle?

Answer 5

40%

Question 6

What is isovolumic contraction?

Answer 6

When the left ventricle is contracting but its pressure is below that of the aorta

Question 7

What is isovolumic relaxation?

Answer 7

When the LV is relaxing and its pressure falls below aortic pressure

Question 8

Which valve opens at the end of IVC?

Answer 8

Aortic

Question 9

Which valve opens at the end of IVR?

Answer 9

Mitral

Question 10

Which valve closes at the beginning of IVC?

Answer 10

Mitral

Question 11

Which valve closes at the beginning of IVR?

Answer 11

Aortic

Question 12

What valve pathology causes decrease in preload and decrease in afterload?

Answer 12

Mitral stenosis

Question 13

What valve pathology causes increase in afterload?

Answer 13

Aortic stenosis

Question 14

What valve pathology causes increase in preload and decrease in afterload?

Answer 14

Mitral regurgitation

Question 15

What valve pathology causes increase in preload?

Answer 15

Aortic regurgitation

Question 16

When do delayed rectifier K+ channels open?

Answer 16

When the membrane depolarises

Question 17

When do inward rectifier K+ channels open?

Answer 17

When the Vm goes below -60mV
(more open when the cells are at rest)

Anchors near Ek

Question 18

What voltage is the threshold for an AP?

Answer 18

-50mV

Question 19

At what voltage do the Na channels close?

Answer 19

+30mV

Question 20

What is the difference between the after-hyperpolarisation and the refractory period?

Answer 20

After-hyperpolarisation = description of the membrane voltage

Hyperpolarisation = description of the cells functional state

Question 21

What happens to permeability during AHP?

Answer 21

Increases K+ permeability and decreases Na+ permeability

Question 22

What is the duration of a ventricular myocyte AP?

Answer 22

up to 500ms

Vary in duration and size - long refractory period so no tetany

Question 23

What is the duration of a neural AP?

Answer 23

1ms

Question 24

What causes the upstroke of the AP in SA node and AV node?

Answer 24

Ca (not Na like in ventricular myocytes)

Question 25

What causes the instability of the resting potential of SA node?

Answer 25

Lack of inward rectifiers

Question 26

What determines the rate of AP firing in the SA node or AV node?

Answer 26

Slope of the pacemaker potential

Question 27

What type of channel is the If channel?

Answer 27

HCN

Question 28

When does If current increase?

Answer 28

During hyperpolarisation

Leads to net inward current

Question 29

What effect does a Na channel block have on the heart?

Answer 29

Reduced conduction velocity

No effect on HR

Question 30

What effect does a Ca channel block have on the heart?

Answer 30

Decreased heart rate and decreased contractile force