B4.008 - Prework 1 - Cardiac Currents and ECG

Question 1

where is the lowest conduction velocity in the heart

Answer 1

AV node

Question 2

where is the hightest conduction velocity in the heart

Answer 2

purkinje fibers

Question 3

what cell types have calcium dependent action potential

Answer 3

SA and AV nodes

Question 4

what cells have sodium dependent action potential

Answer 4

Atrial myocytes bundle of His Purkinje Fibers Ventricular myocytes

Question 5

what does phase 4 represent

Answer 5

Pacemaker potential where the funny sodium current is > Ik

Question 6

What does Phase 0 represent

Answer 6

upstroke of action potential due to IcaL

Question 7

what does phase 3 represent and what is MDP

Answer 7

Repolarization phase where Ik > depolarizing currents

due to delyed rectifier potassium current

Maximun diastolic potential, most negative in SA usually around -50mV

Question 8

what does the slope of phase 4 represent

Answer 8

The slope of phase 4 and the value for the maximum diastolic potential will depend on the balance between the funny sodium current (depolarizing current) and the potassium current (repolarizing current).

Question 9

What do phases 0-4 represent

Answer 9

4 - stable resting potential (inward rectifier potassium channels)

0- Upstroke due to voltage gated sodium current

1 - transient repolarization due to potassium current

2 - plateu phase due to balance between calcium current and potassium current

3 - repolarization due ot potassium current

Question 10

what determines the conduction velocity of the action potential in the AV node

Answer 10

Magnitude of calcium current

Question 11

intrinsic firing rate of SA node

Answer 11

70/min highest

Question 12

Rank the intrinsic firing rates from highest to lowest

AV

bundle of His

Purkinje

SA

Answer 12

SA>AV>bundle of His>Purkinje

Question 13

What determines threshold potential, amplitude of AP, rate of rise of AP and conduction velocity

Answer 13

Magnitude of the L type calcium current in the SA and AV nodes

Question 14

What effect does the sympathetic NS have on ionic currents in SA and AV nodes

Answer 14

Increased If

Increased IcaL

Increased Ik

Question 15

what effect does parasympathetic ACh release have on ionic currents of SA and AV nodes

Answer 15

Decreased If

Decresased IcaL

Decreased Ik (low to moderage vagal activity)

Increased IkACh (at high vagal activity)

Question 16

how does NE increase HR?

Answer 16

makes maximum diastolic potential more positive and phase 4 more steep

Question 17

what determines the rate rise of phase 0 in ventricular myocytes

Answer 17

sodium current

Question 18

what determines the width of the QRS complex and the P wave on ECG

Answer 18

sodium current

Question 19

what mainly determines the duration of ventricular action potential

Answer 19

phase 2 and 3, potassium current

Question 20

NE increases calcium and potassium so….

Answer 20

fater rate of phase 3 repolarization and ecrease induration of ventricular action potential which decreases QT interval

Question 21

effect of NE release from sympathetic nerves in SA node

Answer 21

increased funny sodium current - increased HR

Increased L type calcium - makes threshold more negative

Question 22

effect of NE release from sympathetic nerves in AV node

Answer 22

increased funny sodium current

increased L type calcium current (increased conduction volicity through AV node)

Question 23

effect of NE release from sympathetic nerves in atrial and ventricular myocytes

Answer 23

increased L type calcium current

Increased delayed rectifier potassium current ( deceased AP duration)

Question 24

Answer 24

Question 25

Answer 25

Question 26

Answer 26