cardiac AP

Question 1

Phase 0

Answer 1

rapid upstroke/depolarization
voltage gated Na ch open
Na in

Question 2

baseline set my

Answer 2

K out

Question 3

phase 1

Answer 3

initial repolarization
inactivation of Na ch
voltage gated K begin to open
first dip after phase 0

Question 4

phase 2

Answer 4

plateau
Ca influx balances K efflux
Ca influx triggers Ca release from SR
myocyte contraction

Question 5

phase 3

Answer 5

rapid repolarization
massive K efflux d/t opening slow K ch
closer of Ca ch

Question 6

phase 4

Answer 6

resting potential
high K permeability through K ch
occurs in bundle of his and purkinje fibers

Question 7

cardiac myocytes are electronically coupled to each other by

Answer 7

gap junction

Question 8

myocyte contraction happens during

Answer 8

phase 2

Question 9

Pacemaker phase 0

Answer 9

upstroke
open Ca ch
fast Na ch permanently inactivated
slow conduction velocity used by AV node to prolong transmission from atria to ventricles

Question 10

pacemaker phase 3

Answer 10

repolarization
inactivation of Ca ch
increase activation of K ch
increase K efflux

Question 11

pacemaker phase 4

Answer 11

starting of curve

• slow spontaneous diastolic depolarization d/t funny current
• I(f) flow mixed Na/K inward current
• accounts for automaticity of SA snd AV node
• slope of phase 4 in SA determines HR

Question 12

Things that increase slope of phase 4 in SA node

Answer 12

catecholamines
-increase depolarization and HR
SNS stimulation
-increase chance that I(f) ch open and increase HR

Question 13

things that decrease slope of phase 4 in SA node

Answer 13

ACh/adenosine

• decrease rate of diastolic depolarization
• decrease HR