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Physiology > Cardio Electrophysiology 1 > Flashcards

Cardio Electrophysiology 1 Flashcards

1
Q

What determines the Magnitude (strength) of a cell’s electrical potential?

A

1) Pump mechanisms
2) Membrane Permeability of ions
3) The Electro-chemical gradient

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2
Q

What is the Ionic concentration of a Cardiac Cell?

A

It has a lot of K+ inside the cell

It has a lot of Na+ and Ca2+ outside the cell

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3
Q

Cardiac Cells are extremely permeable to what ion?

A

K+

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4
Q

What are the 2 opposing forces that move K+ across the resting cell?

A

1) Chemical Force (outward)= concentration gradient

2) Electrostatic Force (inward) = K+ ions are attracted to the highly negative charge inside the cell

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5
Q

List the concentrations and equilibriums of Na+:
Extracellular Concentration
Intercellular Concentration
Equilibrium Potential

A

Extracellular: 145 mV
Intracellular: 10 mV
Equilibrium Potential: 70 mV

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6
Q

List the concentrations and equilibriums of K+:
Extracellular Concentration
Intercellular Concentration
Equilibrium Potential

A

Extracellular Concentration: 4 mV
Intercellular Concentration: 135 mV
Equilibrium Potential: -94 mV

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7
Q

List the concentrations and equilibriums of Ca2+:
Extracellular Concentration
Intercellular Concentration
Equilibrium Potential

A

Extracellular Concentration: 2 mV
Intercellular Concentration: 10^-4 mV
Equilibrium Potential: 132 mV

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8
Q

If a cardiac cell has a high concentration of K+, which has a equilibrium potential of -94 mV, how do you explain the resting membrane potential of the cell being -90 mV?

A

Well, there is a Na+ leak, which increases the resting membrane potential from -94 to -90 mV. If the Na+/K+ pump was partially inhibited (Digitalis), the cell will still be able to depolarize, just at a much slower rate.

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9
Q

The ventricular muscle action potential has how many phases?

A

5

Phase 0
Phase 1 
Phase 2 
Phase 3 
Phase 4
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10
Q

How long does the ventricular muscle action potential las?

A

200-300 msec

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11
Q

The duration of the ventricular muscle action potential depends on what?

A

The Interbeat Interval

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12
Q

If the heart rate is 40 beats/min, how long would the Ventricular Muscle action potential be?

A

500 msec

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13
Q

If the heart rate is 150 beats/min, how long would the ventricular muscle action potential be?

A

Less than 200 msec

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14
Q

Draw the ventricular muscle action potential graph. Label the axis and phases. Describe the events occurring in each phase.

A

Really, like draw the freaking graph. :(

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15
Q

When the Fast Na+ channels open, the cell is how much more permeable to Na+ versus K+?

A

The cell is 500x more permeable to Na+ than K+ at the time the Fast Channels open

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16
Q

What causes the end of Phase 0?

A

The closing of the h gate.

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17
Q

What happens to the conductance of K+ during Phase 0?

A

K+ conductance goes down to help keep the cell depolarized.

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18
Q

What is the range of membrane potentials in most mammalian cells?

A

-10 to -100 mV

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19
Q

What are T Type Ca2+ Channels?

A

They are small Ca2+ currents and found mostly in nodal tissue

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20
Q

What are L Type Ca2+ channels?

A

They are long lasting Ca2+ currents that are found mostly in cardiac muscle.

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21
Q

Where are T type channels found? Where are L type channels found?

A

T types: SA nodes and AV nodes

L types: Cardiac Muscle Cells

22
Q

Give an example of a drug that blocks T and L Type Ca2+ channels?

A

Diltiazem, it blocks Ca2+ channels

23
Q

Describe Phases 0 -4.

A

Phase 0: Influx of Na+ thru fast channels generates upstroke
Phase 1: Efflux of K+ generates early partial repolarization
Phase 2: Plateau, Influx of Ca2+ = to Efflux of K+
Phase 3: Efflux of K+
Phase 4: Efflux of K+ > Influx of K+

24
Q

What are the states of the gated channels During Phase 0?

A

The M and H gates are both open.

25
Q

What are the states of the gates during Phases 1-3?

A

The M gate is open, and the H gate is closed.

26
Q

What is the state of the gated channels during Phase 4?

A

The M gates are closed and the H gates are open.

27
Q

What happens to the M and H channel gates when the cell reaches threshold potential?

A

M gates open and H ages open.

28
Q

What is the voltage threshold of a cardiac muscle cell?

A

-70 mV

29
Q

What is the concentration of ions inside and outside of the cell during Phase 4? (Na+, K+, Ca2+)

A

Na+ out > Na+ in
Ca2+ out > Ca2+ in
K+ out

30
Q

What is SCN5A?

A

It is a Na+ channel in Cardiac Muscle Cells.

31
Q

What are the effects of mutations in the Inactivation Gate Loop in SCN5A?

A

The mutations can make people more susceptible to Arrhythmias.

32
Q

If the cardiac muscle cell never had Ca2+ channels, what would the action potential graph look like and why?

A

The Action potential graph would look like a bell curve like a nerve cell.

Ca2+ channels causes the repolarization to last longer. If there was no influx of Ca2+, the cell would just lose ++++ charge, making the potential shoot down really fast.

33
Q

Procaine -

A

Reduces irritability of the cardiac muscle, used in ventricular Arrhythmias

34
Q

Quinidine -

A

Treats atrial fibrillation , atrial flutter, and paroxysmal ventricular tachycardia

35
Q

Tetrodotoxin -

A

blocks Fast Na+ channels

36
Q

Describe the mechanism of action of Procaine and Quinidine.

A

They slow the opening of Na+ gates, reducing depolarization current and slowing condition from cell to cell.

37
Q

What causes the plateau effect in Phase 2?

A

Na+ and Ca2+ slow influx channels. Na+ and Ca2+ slowly leak into the cell together, while K+ conductance is decreased.

38
Q

Ca2+ channel blockers effect what Phase of the action potential?

A

Phase 2 the Plateau phase.

It shortens the plateau phase

39
Q

List some Ca2+ blockers.

A

Verapamil
Nifedipine
Diltiazem

40
Q

Describe some of the effects of Diltiazem

A

There is a slight reduction of the Plateau Phase, but an almost total inhibition of contraction and excitation.

41
Q

Refractory Period -

A

Reduced Excitability

42
Q

Absolute Refractory Period/ Effective Refractory Period -

A

NO EXCITABILITY

During this time not stimulus, no matter how strong will elicit an action potential.

43
Q

In msec, what is the duration of the Absolute Refractory Period, during a Cardiac Action potential?

A

50-275 msec

44
Q

Twitch Force -

A

Is the response due to a stimulus

45
Q

What mechanisms causes Tetanus?

A

Repetitive stimuli at increasing frequency (over stimulation)

46
Q

Why can’t tetanus occur in the cardiac muscle cell?

A

Because tetanus will usually occur during the refractory period, when no action potential can occur. This safe guards the heart since no blood could be pumped during tetanus

47
Q

Relative Refractory Period -

A

LESS EXCITABILITY.
An action potential can be elicited, but:
1) Requires a much stronger stimulus
2) Have a lower amplitude
3) Reduced rate of rise, due to off balance of [Na+] gradient

48
Q

Supernormal Period (SNP) -

A

ENHANCED EXCITABILITY

You only need a small stimulus to produce an action potential, but they propagate slowly.

49
Q

Full Recovery Time (FRT) -

A

The full time required to have normal depolarization and recovery of normal resting excitability.

50
Q

What is the normal time interval for depolarization and resting of a Myocardial Cell? A muscle cell?

A

Myocardial cell: 300-350 msec

Muscle cell: 2-4 msec

51
Q

What is an M gate?

A

It is an activation gate

52
Q

What is an H gate?

A

It is an inactivation gate

Physiology (9 decks)

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