Cardiac Action Potentials

Question 1

Phase 4 of SA node action potential starts at what resting membrane potential?

Answer 1

-60mv

Question 2

what channels first open in phase 4?

Answer 2

funny Na channels from -60 till -50mv

Question 3

which channels open at -50 during phase 4?

Answer 3

transient Ca channels from -50 till -40mv

Question 4

What channels open during phase 0 at -40? and when do they close

Answer 4

long lasting L-type Ca channels

close at +10

Question 5

when does repolarization occur in SA node action potential?

Answer 5

Phase 3 at +10 when DRK channels open

Question 6

What is the resting membrane potential of ventricle and what is the firing level?

Answer 6

RMP = -90

Firing level = -65 (Fast Na channels open and close at +20)

Question 7

When do K2 channels open?

Answer 7

at +20 efflux of K

Question 8

how does the membrane stay at resting potential?

Answer 8

• IRK channels efflux K (main cause)
• influx of Na and Ca along electromagnetic gradient
• Na - K pump (3Na out 2K in)

Question 9

What type of arrhythmia cause blood pooling and is the main cause of stroke in elderly?

Answer 9

Atrial fibrillation

Question 10

Which arrhythmia has a sawtooth appearance and AV node block?

Answer 10

Atrial flutter

Question 11

What is the most serious arrythmia?

Answer 11

Ventricular fibrillation (can reach 300bpm)

Question 12

What is the most common form of arrhythmia?

Answer 12

ventricular extrasystole

Question 13

Which type of heart block has a prolonged PR but maintained P-QRS ratio?

Answer 13

1st degree

Question 14

Which type of heart block is caused by failure of HIS-purkinjie system?

Answer 14

type II Wenckeback or mobitz block (2nd degree)

Question 15

a dropped QRS is present in which heart block?

Answer 15

type I 2nd degree

Question 16

Escape rhythm is found in which heart block? and what is its hallmark?

Answer 16

3rd degree

lack of relationship between P & QRS waves