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NMF: Cardio > Conduction > Flashcards

Conduction Flashcards

1
Q

What is autorhythmicity of the heart?

A

the heart is capable of beating regularly without external factors

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2
Q

What drives the sinus rhythm of the heart?

A

SA node

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3
Q

Do pacemaker cells of the sinoatrial node have a stable membrane potential? what does this allow for?

A

no

generation of an action potential

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4
Q

What changes the membrane potential?

A

movement of ions

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5
Q

What is depolarization?

A

the membrane potential becomes less negative or even positive

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6
Q

What is hyperpolarization?

A

the membrane becomes more negative

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7
Q

What is the resting potential of a pacemaker cell?

A
  • 70 mV
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8
Q

What drives the passive movement of an ion through an ion channel?

A

the electrochemical gradient

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9
Q

What is pacemaker potential?

A

rising depolarisation to the threshold

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10
Q

What causes pacemaker potential?

A

funny currents that allow slow influx of sodium

decreased K+ Efflux
Na+ and K+ influx
transient Ca+ influx

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11
Q

Are voltage-gated Na+ channels hyperpolarising or depolarising?

A

depolarising

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12
Q

Are voltage-gated K+ channels hyperpolarising or depolarising?

A

hyperpolarizing

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13
Q 
Which direction does 
a) sodium
b) calcium
b) potassium
tend to flow?
A

a) in to cell
b) in to cell
c) out of cell

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14
Q

What causes the rising phase of depolarisation in a pacemaker cell?

A

activation of long lasting, L type Ca+ channels causes calcium influx

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15
Q

What causes repolarisation in a pacemaker cell?

A

inactivation of L type Ca+ channels

activation of K+ channels causing K+ efflux

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16
Q

At what membrane potential, do sodium channels become inactive and potassium channels open in a pacemaker cell?

A

+ 40 mV

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17
Q

Which type of transport in a pacemaker cell gets the membrane potential from

a) resting to threshold?
b) threshold to +40?

A

a) mechanic sodium channels

b) voltage-activated sodium channels

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18
Q

Is sodium or potassium conductance earlier on, greater and more short-lived?

A

sodium

19
Q

What are action potentials?

A

brief electrical signals in which the polarity of the nerve cell membrane is momentarily reversed

20
Q

What is the magnitude and velocity of an action potential determined by?

A

it is constant for a given axon

all or none, either there or not

21
Q

What activates voltage-gated channels?

A

depolarization

22
Q

Do voltage-activated calcium channels activate with positive or negative reinforcement?

A

positive: opening of a few channels stimulates others

23
Q

Do voltage-activated potassium channels activate with positive or negative reinforcement?

A

negative: outward movement of potassium repolarizes the cell which turns off the channels

24
Q

What is the refractory period?

A

when a voltage-activated sodium channel enters an inactive state during maintained depolarisation, it requires to be repolarized before another AP can occur

25
Q

What does the refractory period do?

A

it limits the frequency at which any nerve fibre can fire an action potential

26
Q

What is the relationship between diameter of axon and resistance to current flow?

A

the bigger the diameter of axon, the less resistance to current flow

27
Q

How does conduction spread across the atria?

A

cell to cell via gap junctions

28
Q

What happens to conduction in the AV node? what does this allow?

A

delayed

allows atrial systole (contraction) to precede ventricular systole

29
Q

What allows for rapid spread of action potential to the ventricles?

A

The Bundle of His and its branches and the network of Purkinje fibers

30
Q

What is the resting potential for a cardiac myocyte?

A
  • 90 mV
31
Q

What causes phase 0 of a cardiac myocyte action potential?

A

fast Na+ influx causes depolarisation

32
Q

What causes phase 1 of a cardiac myocyte action potential?

A

Closure of Na+ channels and Transient K+ efflux

33
Q

What causes phase 3 of a cardiac myocyte action potential?

A

Closure of Ca++ channels and K+ efflux

34
Q

What is phase 4 of a cardiac myocyte action potential?

A

resting potential

35
Q

What causes the plateau in cardiac myocyte action potential?

A

Influx of Ca++ through L-type Ca++ channels

36
Q

How does the vagus nerve slow the heart rate?

A

Using AcH acting through muscarinic m2 receptors

37
Q

What competes with AcH to inhibit the vagus nerve from slowing HR?

A

atropine

38
Q

What effect does an agent that slows the heart rate have?

A

negative chronotropic effect

39
Q

What does a negative chronotropic effect mean for

a) slope of pacemaker potential
b) frequency of AP?

A

a) decreases

b) decreases

40
Q

What effect does an agent that speeds up the heart rate have?

A

positive chronotropic effect

41
Q

What does a positive chronotropic effect mean for

a) slope of pacemaker potential
b) frequency of AP?

A

a) increases

b) increases

42
Q

What does sympathetic supply have on

a) pacemaker cell K+ efflux?
b) pacemaker cell Na+ and Ca++ influx?

A

a) decrease

b) increase

43
Q

What does parasympathetic supply have on

a) pacemaker cell K+ efflux?
b) pacemaker cell Na+ and Ca++ influx?

A

a) increase

b) decrease

NMF: Cardio (6 decks)

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