Cardiac Action Potential

Question 1

What determines the resting membrane potential

Answer 1

conductance to K+

approaches K+ equilibrium potential

Question 2

Inward current ____ the membrane potential

Answer 2

depolarizes;

brings in + charge

Question 3

OUtward current ____ the membrane potential

Answer 3

hyperpolarizes

pumps out + charge

Question 4

Resting membrane potential of ventricles, atria and purkinje system

Answer 4

• 90 mV (approaches K+ equilibrium potential)

Question 5

ventricles, atria and purkinje system

Phase 0

Answer 5

upstroke of action potential

Question 6

ventricles, atria and purkinje system

Phase 0 is caused by ____

Answer 6

transient increase in Na+ conductance

inward Na+ current until approaches Na+ equilibrium potential at peak of AP

Question 7

ventricles, atria and purkinje system

Phase 1 is the ____

Answer 7

brief period of initial repol

Question 8

ventricles, atria and purkinje system
Phase 1 (Initial repol) is caused by

Answer 8

outward current (by K+ out and decr Na+ in)

Question 9

ventricles, atria and purkinje system

Phase 2 is the ___

Answer 9

plateau of the action potential

Question 10

ventricles, atria and purkinje system
Phase 2 (plateau) is caused by \_\_\_

Answer 10

transient incr in Ca2+ conductance (inward CA2+) and incr K+ out

outward = inward current

Question 11

ventricles, atria and purkinje system

Phase 3 is the ____

Answer 11

repolarization

Question 12

ventricles, atria and purkinje system

Phase 3 is caused by ___

Answer 12

decr Ca2+ inward, incr K+ outward
outward > inward
hyperpolarizes back toward K+ equilibrium potential

Question 13

ventricles, atria and purkinje system

Phase 4 is the ___

Answer 13

resting membrane potential

Question 14

ventricles, atria and purkinje system

Phase 4 is caused by ___

Answer 14

inward and outward currents equal

Vm approaches the K+ equilibrium potential

Question 15

What is the SA node?

Answer 15

pacemaker of the heart

Question 16

____ has an unstable resting potential and exhibits phase 4 depolarization

Answer 16

SA node

Question 17

Latent pacemakers are ___

Answer 17

AV node and His-Purkinje systems

Question 18

What are latent pacemakers

Answer 18

exhibit automaticity and override SA node if it is suppressed

Question 19

Order of rate of phase 4 depolarization

Answer 19

SA node > AV node > His-Purkinje

Question 20

SA node

Phase 0 is the ___

Answer 20

upstroke of the action potential

Question 21

SA node

What causes phase 0

Answer 21

incr in Ca2+ conductance (inward Ca2+ current) towards Ca2+ equilibrium potential

Question 22

SA node

Phase 1 and 2

Answer 22

NO PHASE 1 AND 2 IN SA NODE AP

Question 23

SA node

Phase 3 is the ___

Answer 23

repolarization

Question 24

SA node

What causes phase 3

Answer 24

incr in K+ conductance (outward K+) —> repolarization of membrane potnetial

Question 25

SA node | phase 4 is the ____

Answer 25

slow depolarization

Question 26

SA node | What causes phase 4

Answer 26

pacemaker activity of SA node incr Na+ conductance (inward Na+) turned on by repolarization

Question 27

AV node | Upstroke of AP is due to

Answer 27

inward Ca2+ current (like SA node)

Question 28

What is conduction velocity

Answer 28

time for excitation to spread throughout cardiac tissue

Question 29

what does conduction velocity depend on

Answer 29

size of inward current during upstroke of AP (larger inward current, higher conduction velocity)

Question 30

conduction velocity is fastest in ___ and slowest in ___

Answer 30

fastest in Purkinje | slowest in AV node for ventricular filling before ventricular contraction

Question 31

what is excitability

Answer 31

ability of cardiac cells to initiate AP in response to inward, depolarizing current

Question 32

What is absolute refractory period

Answer 32

from upstroke of AP and ends after plateau NO AP CAN BE INITIATED EVER

Question 33

what is effective refractory period

Answer 33

conducted action potential cannot be elicited slightly longer than the absolute refractory

Question 34

what is the relative refractory period

Answer 34

after absolute refractory period when repol almost complete when an AP can be elicited but more than usual inward current required