16 Cardiac electrophysiology

Question 0

In which part of the heart do perkinji fibers lie?

Answer 0

In the endocardium

Question 1

What does phospholamban do?

Answer 1

-Phosphorylating phospholamban (PLB) relieves its inhibition on the SR Ca++ pump in cardiac muscle, thus resulting in weaker contraction due to less Ca++ in the cytoplasm

Question 2

Which part of the heart is the last area to depolarize during systole?

Answer 2

The epicardium at the base. (this would be in the ventricle)

Question 3

The route of electrical impulse through the heart?

Answer 3

SA node, through atria, AV node (delay), bundle of His, left and right bundle branches, perkinji fibers

Question 4

which area of the heart is the pacemaker?

Answer 4

the SA node

Question 5

What is the internodal pathway?

Answer 5

They use it to explain the route through the atria form SA to AV node.

Question 6

What is the only electrical conduction pathway between the atria and the ventricles?

Answer 6

The AV node.

Question 7

Which heart cells have the fastest conduction rate?

Answer 7

Purkinji fibers at 4 M/S

Question 8

What makes the perkinji fibers the fastest conducting cells in the heart?

Answer 8

Large diameter

Large number of Na+ channels

Question 9

T/F the electrical impulse of the heart spreads from epicardium to endocardium?

Answer 9

False, Because the perkinji fibers are in the endocardium, it spreads from inside out; or endocardium to epicardium.

Question 10

What does digitalis do? What is another name for digitalis?

Answer 10

Inhibits the Na/K+ pump, and its also known as digoxin.

Question 11

Which ion in the cell sets the resting membrane potential? How does it do it?

Answer 11

K+

It is because it is the leakiest.

Question 12

The outward directed K+ leak current is primarily due to what?

Answer 12

The inward rectifier Ik (Ikir) chanel

Question 13

About how much K+ needs to leak out of the cell to establish the resting membrane potential?

Answer 13

Very little. (0.004% of intracellular K+)

Question 14

What is the concentration of sodium on the inside of a cell? on the ouside?

Answer 14

inside= 10 mm (mm is milimolar)

outside=145 mm

Question 15

what is the concentration of K+ on the inside of a cell? on the outside?

Answer 15

inside= 120 mm
outside= 4.5 mm

Question 16

Review the Na+ channel.

Answer 16

Impulse, quick activation gate (initially closed) but also slow inactivation gate started at threshold, open then becomes closed, absolute refractory period, relative refractory period.

Question 17

What is the isoelectric/gradient point in a cell for Na+?

Answer 17

+60 This means that if it gets to +60, sodium would no longer want to have a net influx.

Question 18

In cardiomyocytes, what causes phase 0?

Answer 18

Influx of Na+ and Ca+ which causes depolarization.

recall that cardiomyocytes have fast action potentials

Question 19

What causes phase 1 in cardiomyocytes?

Answer 19

The closure of fast Na+ channels. This causes a slight repolarization drop.

Question 20

what causes phase 2 in the cardiomyocyte?

Answer 20

2 Parts;

a) T- type Ca+ channels inactivate rapidly lowering the peak.
b) L- Type Ca+ channels inactivate slowly causing the plateau of phase 2

Question 21

What causes phase 3 in the cardiomyocyte?

Answer 21

influx of K+. (The K+ channels are slow but is causes repolarization through the delayed rectifier K+ channels)

Question 22

What causes phase 4 in the cardiomyocyte? what does phase 4 look like?

Answer 22

Phase 4 is maintained by the K+ leak channels at a constant resting membrane potential of about -80mv.
The line on the graph is the horizontal line.

Question 23

So, what causes the plateau in the cardiomyocyte action potential?

Answer 23

the slow closing L-type Ca+ channels

Question 24

The SA node and AV node have fast of slow action potentials?

Answer 24

Slow.

Question 25

What causes phase 0 in the SA node?

Answer 25

Ca+ influx only! These cells do not have Na+ channels.

Question 26

what causes phase 1 and 2 in SA nodal cells?

Answer 26

Trick question because these phases do not exist in slow type action potentials.

Question 27

what causes phase 3 in the SA node?

Answer 27

opening of the K+ channels and closing of the Ca+ channels

Question 28

what causes phase 4 in the SA node?

Answer 28

If (funny channels) ICa+ (calcium flows into cells more) IK+ (slowly becomes less leaky)

Question 29

What effect does Cl- have on the action potential of the SA node?

Answer 29

Very little for our purposes so just ignore it. (it would move into the cell slowly though)

Question 30

What does phase 4 of a SA node look like on the graph?

Answer 30

A positive slope. This is because funny channels allow cations to move in, Ca+ becomes more permeable, and the K+ leak channels become less leaky.

Question 31

what do funny channels do?

Answer 31

they have a slow inward cation current that starts once the cell reaches hyperpolarization. Causes the cell to become a little bit more + and closer to threshold.

Question 32

what is the threshold potential for slow action potentials? fast action potentials?

Answer 32

slow=-35mv | fast=-65 mv

Question 33

what is the conduction velocity of slow action potentials? fast action potentials?

Answer 33

slow velocity= .1 m/s | fast velocity= 3 m/s

Question 34

what phase of slow action potential do you see the opening of the Na+ channels?

Answer 34

None! these do not have Na+ channels. Just a reminder.

Question 35

what will be the result of decreasing the slope of phase 4 in the slow action potential?

Answer 35

a slower heart rate.

Question 36

what would be the result of increasing (more +) the threshold of a slow action potential in the SA node?

Answer 36

slow heart rate. this is because it would take a little bit longer to reach the value.

Question 37

what would be the effect of hyperpolarizing the slow action potential in the SA node?

Answer 37

slower heart rate. This is because it takes more time to reach the regular -35 mv if your more negative.

Question 38

Normal rate of depolarization for SA node? AV node? cardiomyocytes?

Answer 38

1) 60-100 bpm 2) 40-50 bpm 3) 40 bpm

Question 39

What does an EKG pick up?

Answer 39

current that is moving on the outside of the cell. This will be opposite of the inside movement.

Question 40

How do you calculate conduction velocity? (the equation)

Answer 40

(conduction velocity)=change in voltage/resistance (also said as V=IR)

Question 41

what 2 things cause a change in voltage in the V=IR equation?

Answer 41

amplitude (resting to action potential height) | slope (of the action potential such as in phase 4)

Question 42

what effect would increasing K+ concentrations outside to cell do?

Answer 42

slow action potentials. If too much was outside, an action potential would not fire.

Question 43

T/F If you have enough gap junctions, you have nearly zero resistance?

Answer 43

true

Question 44

T/F larger muscle fibers have less resistance?

Answer 44

true

Question 45

What does the action potential look like during phase 0 of a cardiomyocyte if it contracts during the relative refractory period?

Answer 45

The normal straight up line now has a slight slope. This is because there are many Na+ channels that are still closed.

Question 46

which cells have the largest diameter in the heart?

Answer 46

1) purkinji cells and HIS bundle cells (50 micro m.) 2) atrial and ventricular myocytes (12 micro m.) 3) SA and AV nodal cells (7 micoro m.)

Question 47

which heart cells conduct the fastest?

Answer 47

Purkinji and His bundle cells followed by cardiomyocytes, followed by SA and AV nodal cells.

Question 48

what are the shapes of nodal cells? ventricular myocytes? purkinji cells?

Answer 48

nodal cells= round, ovoid myocytes= cylindrical purkinji cells= cylindrical

Question 49

which cells in the heart conduct the fastest? slowest?

Answer 49

``` fastest= purkinji cells slowest= nodal cells. ```

Question 50

What activates the funny channels during phase 4?

Answer 50

Hyper polarization

Question 51

what is the concentration of Ca+ on the side of a cell? on the outside?

Answer 51

inside=.0001 mm | outside= 1.0 mm