5 – Action Potentials

Question 1

Sodium channel types:

Answer 1

-slow Na+
-fast Na+

Question 2

Slow Na+ channel:

Answer 2

-funny pacemaker current
-early phase 4 in cardiac nodal cell AP

Question 3

Fast Na+ channel:

Answer 3

-rapid depolarization
-phase 0 in cardiomyocyte AP

Question 4

Calcium channel types:

Answer 4

-T-type
-L-type

Question 5

T-type calcium channel:

Answer 5

-transient current
-late phase 4 in nodal cell AP

Question 6

L-type calcium channel:

Answer 6

-sustained current
-late phase 4 and 0 in nodal cell AP
-plateau and phase 2 in cardiomyocyte AP

Question 7

Autorhythmic cells and APs:

Answer 7

-spontaneously fire Aps
-depolarization then spreads to adjacent contractile cells through gap junctions

Question 8

Autorhythmic cell:

Answer 8

-no resting potential
-pacemaker potential: depolarization
-slow depolarization phase

Question 9

Phases of a cardiac nodal cell AP:

Answer 9

-phase 4
-phase 0
-phase 3

Question 10

Phase 4 of cardiac nodal cell AP:

Answer 10

-pacemaker Na+ influx
-Ca2+ channels recover from inactivation
-pumps restore ion gradients

Question 11

Phase 0 of cardiac nodal cell AP:

Answer 11

-Ca2+ influx
>depolarization

Question 12

Phase 3 of cardiac nodal cell AP:

Answer 12

-Ca2+ channels inactivate
-delayed K+ efflux
>repolarization

Question 13

Autorhythmic cell potential change during an autorhythmic cell AP:

Answer 13

-pacemaker potential
-rapid depolarization phase of AP
-repolarization phase of AP

Question 14

Pacemaker potential steps:

Answer 14

1. Initial period of spontaneous depolarization to subthreshold
2. Latter period of spontaneous depolarization threshold

Question 15

Initial period of spontaneous depolarization to subthreshold:

Answer 15

-funny channels open (slow Na+)
>sodium moves in
>potassium moves out

Question 16

Latter period of spontaneous depolarization threshold:

Answer 16

-T-type calcium channels open
>calcium moves in

Question 17

Rapid depolarization phase of AP:

Answer 17

-L-type calcium channels open
>calcium moves in

Question 18

Repolarization phase of AP:

Answer 18

-potassium channels open
>potassium moves out

Question 19

What does SNS do to the phase 4 slope (depolarization)?

Answer 19

-increases slope

Question 20

What does PNS (vagal) do to the phase 4 slope?

Answer 20

-decreases slop

Question 21

Effects of autonomic NS on SA nodal cells: PNS

Answer 21

-acts directly on K+ and T-Ca+ channels
>increase K+ efflux
>decrease Ca2+ influx
-decrease cAMP
*greater state of hyperpolarization

Question 22

Effects of autonomic NS on SA nodal cells: SNS

Answer 22

-acts via PKA on Funny and T-Ca2+ channels
>not coupled directly to channels=needs a messenger=slower
-increase Na+ and Ca2+ entry
*greater state of depolarization

Question 23

Bradycardia (PNS):

Answer 23

-slow HR

Question 24

Tachycardia (SNS):

Answer 24

-fast HR

Question 25

Cardiomyocyte:

Answer 25

-negative resting potential
-rapid depolarization
-plateau phase

Question 26

Phases of cardiomyocyte AP:

Answer 26

-0: rapid depolarization
-1: small repolarization
-2: plateau
-3: repolarization
-4: resting polarization

Question 27

Phase 0: rapid depolarization

Answer 27

-sodium channels open
>sodium moves in

Question 28

Phase 1: small repolarization

Answer 28

-sodium channels become inactivated
>sodium movement in decreases
-fast K+ efflux

Question 29

Phase 2: plateau

Answer 29

-K inward channels close
>K movement out decreases
-Ca2+ L-type channels open
>Ca2+ moves in

Question 30

Phase 3: repolarization

Answer 30

-K delayed channels open
>K moves out
-Ca2+ L-type channels close
>Ca2+ movement in decreases

Question 31

Phase 4: resting potential

Answer 31

-K channels (both types) open
>K moves out
-Na and calcium channels remain closed (recover from inactivation)
>little sodium or calcium moves in
*pumps restore ion gradients

Question 32

Cadiomyocytes AP:

Answer 32

-no summation
>inactive during refractory period (absolute and refractory)
-delay between electrical activity and mechanical action
*relaxation of ventricles necessary for filling

Question 33

What channels are involved in initiating or maintaining nodal cell and cardiomyocyte depolarization?

Answer 33

-sodium and calcium channels

Question 34

Muscarinic receptors act predominantly on this/these channels:

Answer 34

-calcium and potassium channels
>GCP: is directly linked to both channels