Electrophysiology Lecture 1 -- Ion Channels and Action Potential Flashcards Preview

Block C - Circulation > Electrophysiology Lecture 1 -- Ion Channels and Action Potential > Flashcards

Flashcards in Electrophysiology Lecture 1 -- Ion Channels and Action Potential Deck (26):
1

Define current

Movement of positive ions per unit time

2

Reason for slow channel AP in AV node

To ensure proper timing (allows good LV filling)

3

Fast channel tissue in the heart

Working atrial muscle His-Purkinje system Working ventricular muscle

4

Slow channel tissue in the heart

Sinoatrial node Atrioventricular node

5

Dominant current in phase 4

IK1

6

Dominant current in phase 0

INa

7

Dominant current in phase 2

Balance between ICa and IK1

8

Dominant current in phase 3

IKr

9

Describe the events of phase 1

A brief increase in K+ current rapidly but only partially repolarizes the cell to lead in to the plateau phase

10

Describe the events of phase 3

Final rapid repolarization caused by opening of a specific type of K+ channels

11

Name of K+ channels involved in phase 3

Delayed-rectifier channels

12

Time constants for opening of the relevant ionic channels

Na+ = 1 ms

Ca+ = a few ms

K+ = 100s of ms

13

Reason for long time constant of K+ channel opeing

14

Define APD

Action Potential Duration = the interval between depolarization and complete repolarization

15

Define refractory period

The interval between depolarization and repolarization until -60 mV before a new action potential can be fired

16

Equilibrium potentials of relevant ions

K+ = -90 mV

Na+ = +60 mV

Ca++ = +60 mV

17

Where is If expressed?

His-Purkinje system and SAN/AVN

18

Membrane potential from end of phase 3 until the next action potential in working atrial and ventricular muscle

Constant (-80 or -90 mV)

19

Phase 4 potential in His-Purkinje tissue

Gradually depolarizes due to inward Na+ movement through a pacemaker channel carrying If

20

Resting potential of slow-channel tissues

-60 mV

21

Significance of slow channel tissue resting potential

Sodium channels are deactivated when membrane potential is -60 mV or more, so the membrane relies on Ca++ influx for depolarization (innately slower reaction)

22

Compare fast channel vs. slow channel tissues

Fast = Na+, fast activation, large max current, small sensitivity to ANS

Slow = Ca++, slow activation, small max current, high sensitivity to ANS

23

Define the relative refractory period/post-repolarization refractoriness

Period after complete repolarization where the membrane is hyperpolarized past its resting potential

24

What does automaticity depend on?

Spontaneous phase 4 depolarization

25

3 major determinants of spontaneous automatic rate

  • Maximum diastolic potential (most negative potential from which phase 4 depolarization takes place)
  • Slope of phase 4 (rate of spontaneous phase 4 depolarization)
  • Threshold potential

26

Purpose of If

Open when cell repolarizes to allow spontaneous firing