MP and AP Flashcards


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1

What is the primary role of cardiac myocytes?

Conraction

2

How is contraction initiated?

Action potential

3

What is action potential (AP)?

Transient change in polarization of resting membrane potential

4

Cardiac myocytes have an ___________________ b/w the intracellular and extracellular regions.

Electrical potential difference

5

The intracellular region of cardiac myocytes is _____________ charged relative to the extracellular region

Negatively

6

A resting ventricular myocyte has a resting membrane potential of ________ relative to the extracellular env.

-90 mV

7

What is the charge of the extracellular environment of a resting ventricular myocyte?

0 mV

8

T/F: The cardiac myocyte in a resting state is said to be depolarized, meaning there is charge separation b/w interior and exterior environments of the cell.

False

9

The Em is determined by _________________

[ion] differences

10

Which four ions are primarily involved in determining the membrane potential during the cardiac cycle?

  • Na+
  • K+
  • Ca++
  • Cl-
11

The current of cell membranes is carried by ______

ions

12

Which ion is most important for establishing the resting membrane potential?

K+

13

T/F: Ohm's Law states that the voltage difference b/w two points in a material are indirectly proportional to the current (I) and the resistance (R)

False

14

T/F: The inverse of current (I) is known as conductance (g).

False

15

V =

I*R

16

I = ΔV(1/R) =

ΔV*g

17

What factors are involved in the membrane potential?

  1. Type of cell
  2. [Ionic] differences
    1. Chemical gradient
    2. Electrochemical forces
  3. Permeability of cell membrane
  4. Electrogenic pumps
18

[K+] is _______ (high/low) on the inside of the cell.

High

19

Where will K+ want to move?

From inside to outside

20

Where will Na+ want to move?

From outside to inside

21

Where will Ca++ want to move?

From outside to inside

22

What equation can be used to calculate ion equilibrium?

Nernst

23

T/F: EK is not the same as Em because EK is less negative than Em

False

24

Why is there a small net electromotive driving force resulting in steady and slow leakage of K+ in resting nonpacemaker cardiomyocytes?

Negative voltage required to stop outward flow of K+ is not strong enough

25

What is responsible for the flow of K+ ions in the resting state?

Inward rectifier potassium channel (KI1)

26

The higher the permeability, the higher the ______________, meaning the greater the solute transport across the cell membrane

conductance

27

Where is the Na/K pump located?

Sarcolemma

28

If the ATPase Na/K pump is inhibited, what happens to intracellular Na?

Increases

29

Na/Ca exchanger rate (Na:Ca)

3:1

30

Na/K exchanger rate (Na:K)

3:2

31

A flux of positive charge into the resting cell results in a(n) __________ (inward/outward) current and ___(de-/hyper-)polarization of the cell.

Inward; depolarization

32

A flux of positive charge out of the resting cell results in a(n) __________ (inward/outward) current and ___(de-/hyper-)polarization of the cell.

Outward; hyperpolarization

33

T/F: Ion channels are glycosylated ptns w/ repeating domains

True

34

Each domain of ion channels consists of _____ transmembrane segments

6

35

Which ion channel has 4 domains that are not bonded together by peptide bonds?

K+

36

Which loop on the Na channel is believed to be the inactivation gate?

B/w domain III and IV

37

On the Na channel, where is the M gate located?

Outer side

38

On the Na channel, where is the H gate located?

Inner side

39

When a membrane is depolarized, which Na gate (H or M) rapidly opens allowing Na into the cell?

M

40

When does the H gate begin to close?

When the M gate starts to open, completely closes when cell starts to undergo repolarization

41

Sudden depolarization of membrane potential in cardiomyocytes via ion current results in __________

Action potential

42

List the 2 general types of cardiac APs

  • Nonpacemaker ("fast response")
  • Pacemaker ("slow response")
43

These cells are triggered by APs in adjacent cells w/ depolarizing currents

Nonpacemaker

44

These cells can spontaneously generate their own APs

Pacemaker

45

The nonpacemaker and pacemaker APs of the heart are different in their ______ and ______ than the APs found in nerve cells and skeletal muscle cells.

Shape; duration

46

Which cells have a true resting potential?

Nonpacemaker

47

Nonpacemaker AP is divided into how many phases?

5

48

Which phase of nonpacemaker cell:

Equilibrium maintained by high gK+ through inward rectifying K channel compared to low gNa+ and gCa++. This is true resting potential.

Phase 4

49

Which phase of nonpacemaker cell:

Rapid depolarization due to increase in Na conductance of voltage-gated fast ion Na channels. Rush of Na into cell.

Phase 0

50

Which phase of nonpacemaker cell:

Repolarization due to opening of transient outward K channel incombo w/ inactivation of Na channel. gCa++ increased and slow movement of Ca into cell via L-type Ca channel.

Phase 1

51

What channel is known as the slow inward, long-lasting current?

L-type Ca channel

52

Which phase of nonpacemaker cell:

Inward movement of Ca through lon-lasting (L-type) voltage gated Ca ion channel = major pathway of entry for Ca

Phase 2

53

Which phase of nonpacemaker cell:

Repolarization phase. gK conductance increases and initiates an outward K current through K delayed rectifier and gCa conductance decreases

Phase 3

54

Ventricular cells are unexcitable (refractory) during which phases (absolute refractory period)?

0, 1, 2

55

What does the effective refractory period include?

Absolute refractory period and some of phase 3

56

Which refractory period:

Weaker than normal APs may be generated and conducted.

Relative Refractory Period

57

Which refractory period:

Weaker than normal APs may be generated

Supranormal period

58

Which refractory period:

Only localized APs can be generated, but not propagated.

Effective Refractory Period

59

Which refractory period:

No new propagating APs are generated

Absolute refractory period

60

If the fast response Na channels are blocked/inactivated, the AP upstroke is reduced and can lead to ___________

Arrhythmias

61

During phase 3 or phase 4, nonpacemaker cells may start generating spontaneous depolarizations called _________________.

Afterpolarizations

62

T/F: The depolarizing current in an afterpolarization is from the fast response Na channel, given that the slow Ca channels are closed.

False

63

If a drug interacts w/ __________________ it can lead to dangerous arrhythmias

K delayed rectifier

64

T/F: Pacemaker cells have no true resting potential

True

65

What phases are the pacemaker AP divided up into?

0, 3, 4

66

Pacemaker cells are ______ and referred to as _________ AP compared to the "fast response" nonpacemaker cells.

Slow; slow response

67

What ion is responsible for being the major depolarizing current in pacemaker cells?

Ca (via long-lasting (L-type) voltage gated Ca channel)

68

Which phase of a pacemaker cell:

  1. gK decreases
  2. gCa is increasing (in second half of this phase) due to transient (T-type) Ca channels
  3. Pacemaker current (funny Na ion current)
  4. L-type Ca channels start to open

Phase 4

69

Which phase of a pacemaker cell:

  1. Inward movement of Ca via L-type Ca channels = depolarizes
  2. Simultaneous decrease in K channels currents
  3. Slope is "softer" than same phase of nonpacemaker cells

Phase 0

70

Which phase of a pacemaker cell:

Repolarization begins due to decrease in gCa and increase in gK

Phase 3

71

What is the primary pacemaker site?

SA node

72

What order of nodes would take over if the SA node failed?

SA node > AV node > Bundle of His > Purkinje fibers

73

The higher intrinsic "firing" rate of the SA node controls the other nodes. This is termed _____________

Overdrive suppression

74

If the SA node is no longer controlling, secondary pacemaker sites will develop. When this happens, the new site outside of the SA node is referred to as an ______________

Ectopic focus

75

What mechanisms can modify the SA node AP?

  • Change slope of phase 4
  • Alter the threshold voltage
  • Change the hyperpolarization
76

What are the effects of sympathetic stimulation on the SA node?

Curve will shift to the left, meaning the AP will kick in faster

77

What are the effects of vagal (parasympathetic) stimulation on the SA node?

Curve will shift to the right, meaning the AP will take longer to kick in

78

List factors that would increase the SA node firing rate

  1. Sympathetic stimulation
  2. M antagonists
  3. Beta agonists
  4. Circulating catecholamines
  5. Hypokalemia
  6. Hyperthyroidism
  7. Hyperthermia
79

List factors that would decrease the SA node firing rate

  1. Parasympathetic stimulation
  2. M agonists
  3. Beta blockers
  4. Ischemia/hypoxia
  5. Hyperkalemia
  6. Na and Ca blockers
  7. Hypothermia