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Cardiovascular Science > Generating the cardiac rhythm > Flashcards

Generating the cardiac rhythm Flashcards

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Biology 101 flashcards
1
Q

What is heart muscle able to do without the input of nerves?

A

Depolarise and contract rhythmically

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2
Q

What are the three types of cardiac action potential?

A

SA and AV nodes
Atrial muscle
Purkinje fibres and ventricular muscle

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3
Q

In what three ways do cardiac action potentials differ from each other and also from action potentials in muscles or nerves?

A

Duration
Shape
Ionic basis of depolarisation

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4
Q

Where is the sino atrial node located?

A

Wall of right atrium where superior vena cava enters

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5
Q

Does the sino atrial action potential have a resting membrane potential?

A

No

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6
Q

How many action potentials does the SA node have per minute?

A

100

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7
Q

Is this rate of 100 AP/min changing?

A

It constantly changes as the SA node is a pacemaker

100 beats per minute is the intrinsic rate

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8
Q

Describe what is happening in the rising limb of the SA node action potential

A

Inward movement of Na+
Decreased conductance of K+
Inward movement of Ca+

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9
Q

What is the cardiac equivalent of a resting membrane potential?

A

Pacemaker potential

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10
Q

Describe what is happening when the action potential fires

A

Inward movement of Ca+ depolarises the cell
Decrease of conductance of K+ continues
Cell repolarised by outward movement of K+

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11
Q

If the intrinsic rate of the SA node is 100 beats per minute, why is resting heart rate closer to 70 beats per minutes?

A

Vagal tone

Parasympathetic vagal nerve innervates the atria

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12
Q

Where do sympathetic nerves that innervate the heart exit the spinal cord?

A

T1-L2

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13
Q

How is heart rate controlled?

A

Autonomic nervous system

By altering pacemaker potential

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14
Q

How does increased parasympathetic vagal activity lower the heart rate?

A

Hyperpolarising cells
Opens K+ channels
Reduces gradient of pacemaker potential
Takes longer to reach threshold

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15
Q

What does negative chronotropic mean?

A

Slows heart rate

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16
Q

How is heart rate neuronally increased at SA node?

A

Sympathetic nervous system
Noradrenaline
Beta1 receptors
Increased Na+ and Ca+ conductance

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17
Q

How is heart rate hormonally increased at the SA node?

A

Adrenaline acting on beta1 receptors

Increased Na+ and Ca+ conductance

18
Q

What does functional synctium mean?

A

All cells are structurally and electrically coupled together and so their behaviour reflects that of one muscle cell

19
Q

What allows current to flow between adjacent cardiac cells?

A

Gap junctions

20
Q

Why is the SA node the pacemaker as opposed to the AV node?

A

It is faster and so dictates pace

21
Q

How quickly does conduction move through the atria?

A

0.5m/s

22
Q

How long does it take an impulse to travel from the SA node to the AV node?

A

0.09s

23
Q

What is the pacemaker rate of the AV node?

A

40 beats per minute

24
Q

What is the conduction rate at the AV node?

A

0.05m/s

25
Q

What does AV delay ensure?

A

Atrial depolarisation, contraction and ejection before the ventricles depolarise

26
Q

Where does the current flow after the AV node?

A

Through the bundle of His and the the Purkinje fibres

27
Q

At what speed does current flow through the bundle of His?

A

2m/s

28
Q

At what speed does current flow through the Purkinje fibres?

A

4m/s

29
Q

Is AV delay constant?

A

No it changes in response to heart rate, e.g. with exercise

30
Q

What is an ectopic beat?

A

Random ventricular contraction with no stimulation

31
Q

In what order does the ventricle depolarise?

A

From the endocardium to the epicardium,

32
Q

What is the resting potential of a ventricular myocyte?

A

-80 to -90

33
Q

What are the phases of ventricular myocyte action potentials?

A 
0 rapid deoplarisation
1 partial repolarisation
2 plateau
3 repolarisation
4 resting potential
34
Q

What is responsible for 0?

A

Inward movement of Na+

Through fast voltage gated channels

35
Q

What is responsible for 1?

A

Inactivation of Na+ channels

36
Q

What is responsible for 2?

A

Inward Ca+ movement and outward movement of K+

Momentarily in equilibrium

37
Q

What is responsible for 3?

A

Outward movement of K+

38
Q

How long is the absolute refractory period of a ventricular myocyte?

A

200ms

39
Q

What is different between skeletal muscle and ventricular muscle twitch and the delay after an action potential?

A

Ventricular muscle contracts while the action potential is firing
Skeletal muscle contracts after the action potential has occurred

40
Q

Is tetanic contraction possible in cardiac muscle?

A

No

Cardiovascular Science (12 decks)

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