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Cardiovascular System (Milly's) > Electrical Mechanisms > Flashcards

Electrical Mechanisms Flashcards

1
Q

What ion concentration sets up the RMP in cardiac cells?

A

K+

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2
Q

What are the intra and extracellular concentrations of K+ roughly in the body?

A

Intra-140mM

Extra-4mM

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3
Q

When are cardiac myocytes most permeable to K+?

A

At rest

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4
Q

What is Ek roughly?

A

-95mV

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5
Q

Why does the RMP not equal Ek exactly?

A

Because there is some very small permeability to other ion species at rest

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6
Q

During action potentials what happens to the cystolic Ca2+ conc?

A

It is increased

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7
Q

Why is calcium needed in cells during contraction?

A

Allows actin and myosin interactions

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8
Q

Roughly how long is the wave in a cardiac myocyte action potential?

A

300-400 ms

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9
Q

What is the ratio of systole to diastole in a ventricular cardiac cell action potential?

A

1:2

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10
Q

What ion channel is responsible for the upstroke in the ventricular cardiac action potential?

A

Voltage gated Na+ channels

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11
Q

What is the initial re-polarisation of the ventricular cardiac action potential caused by?

A

A transient outward K+ current

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12
Q

What ion channels are responsible for the plateau phase of the ventricular cardiac action potential

A

V-gated Ca2+ channels (L-type)

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13
Q

Why does the plateau phase of the ventricular cardiac action potential still continue to decrease slightly?

A

Because there are some K+ channels open also

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14
Q

When the membrane potential becomes increasingly positive, what happens to the Na+ channels?

A

The are inactivated

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15
Q

What is the large down stroke of the ventricular cardiac action potential graph caused by?

A

The inactivation of Ca2+ channels (L-type) and opening of voltage gates K+ channels

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16
Q

What is different about the cardiac myocytes that create the SA node? (2)

A
  • They do not have much contractile ability

- no proper RMP

17
Q

What is the minimum potential a cardiac myocyte in the SA node ever reaches as a membrane potential?

A

-60mV

18
Q

When looking at a graph of a SA node action potential, what is the initial slope to threshold called?

A

The funny current

19
Q

What channel causes the funny current of the SAN action potential?

A

HCN (hyperpolarisation-activated, cyclic nucleotide-gates channels )

20
Q

What ion causes the funny current in a SAN action potential?

A

Na+ (influx into the cell- depolarises the cell)

21
Q

At what potential is a HCN channel activated?

A

-50mV (more negative the potential the more likely it is that the HCN channels will open)

22
Q

What causes the upstroke of the SAN action potential?

A

Opening of voltage gated Ca2+ channels (L-type)

23
Q

What causes the re-polarisation of the membrane during a SA node action potential?

A

The opening of Voltage gated K+ channels

24
Q

What is different about the RMP in normal cardiac cells and then the RMP of the cells in the SAN and AVN?

A

Those in the SAN and AVN have no proper/unstable resting potential

25
Q

Why is SA node the thing to set the rhythm of the heart?

A

It is the fastest to depolarise

(There are other parts of the heart- AVN and purkinje fibre that have automaticity but they depolarise slower so are not the pacemakers)

26
Q

What happens if the action potentials in the heart fire too slowly?

A

Bradycardia

27
Q

What happens if the action potentials in the heart fail to fire?

A

Asystole

28
Q

What happens if the action potentials in the heart fire to quickly?

A

Tachycardia

29
Q

What happens if the electrical activity of the heart becomes random?

A

Fibrillation

30
Q

What can fibrillation cause a loss of?

A

Cardiac output

31
Q

What is the normal plasma K+ conc?

A

3.5-5.5mmol/L-1

32
Q

What will happen to the interval between APs created by the pacemaker cells if the membrane depolarised more rapidly during diastole? How will this effect the heart rate?

A

The interval will decrease meaning there is a faster heart rate- tachycardia

33
Q

What will happen to the heart rate if the pacemaker potential depolarises less rapidly?

A

Bradycardia- slower heart rate because the interval between action potentials increases

Cardiovascular System (Milly's) (28 decks)

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