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Cardiovascular System > Electrical Activity of the Heart > Flashcards

Electrical Activity of the Heart Flashcards

1
Q

In order for the whole heart to shorten on contraction, what two kinds of connections between the two membranes are needed?

A
  • physical

- electrical

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2
Q

The arrangement of desmosome-gap junction-desmosome is known as

A

intercalated discs

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3
Q

Are action potentials in cardiac muscle longer or shorter than those in skeletal muscle?

A

Longer

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4
Q

The amount of calcium entering the heart from outside can be regulated by cardiac muscle, this allows what to be regulated?

A
  • number of gap junctions

- strength of contraction

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5
Q

During what phase of the action potential does calcium enter the cardiac muscle cell?

A

Plateau phase

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6
Q

Through what channels does calcium enters cardiac muscle cells?

A

L-type voltage-gated calcium channels

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7
Q

Calcium sensitive calcium release channels in the sarcoplasmic reticulum release stored calcium into the cytoplasm though what process?

A

Calcium-induced calcium release

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8
Q

The combination of calcium release and calcium entry across the membrane causes a rapid increase in calcium concentration which

A

initiates contraction

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9
Q

What process is entirely responsible for calcium release from the sarcoplasmic reticulum?

A

Calcium-induced calcium release (CICR)

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10
Q

How are crossbridges formed?

A

Myosin heads protruding from the thick filament bind to sites on actin

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11
Q

At rest, the myosin binding sites on the actin are covered by what regulatory protein?

A

Tropomyosin

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12
Q

When calcium binds to troponin, there is a conformational change involving the dissociation of what?

A

Troponin from actin

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13
Q

What happens regarding tropomyosin when troponin dissociates from actin?

A

Tropomyosin shifts out of actin cleft, uncovering the actin binding sites for myosin

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14
Q

When myosin bridges form, what develops?

A

Tension

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15
Q

Tension is related to the number of

A

active crossbridges

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16
Q

What happens to calcium when ATP-dependent calcium pumps in the tubular part of the sarcoplasmic reticulum are activated?

A

Calcium is sequestered from the cytosol back into the sarcoplasmic reticulum

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17
Q

As the action potential repolarises what happens to the heart muscle?

A

Heart muscle relaxes

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18
Q

Cardiac muscle is electrically connected via

A

gap junctions

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19
Q

Cardiac muscle is physically connected by

A

desmosomes

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20
Q

Why does cardiac muscle not exhibit tetanic contraction?

A

It has a long refractory period

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21
Q

Cells with unstable resting membrane potential act as

A

pace makers

22
Q

In a non-pacemaker action potential, there is a high resting membrane potential for what ion?

A

K+

23
Q

What changes in permeability to ions occur in the plateau phase in a non-pacemaker action potential?

A
  • increase in permeability to Ca2+

- decrease in permeability to K+

24
Q

What changes in permeability to ions occur in the initial depolarisation of non-pacemaker action potentials?

A

Increase in permeability to Na+

25
Q

What changes in permeability to ions occur in the repolarisation phase of non-pacemaker action potentials?

A
  • decrease in permeability to Ca2+

- increase in permeability to K+

26
Q

Pacemaker potential is due to what 3 factors?

A
  • gradual decrease in permeability to K+
  • early increase in permeability to Na+
  • late increase in permeability to Ca2+
27
Q

The action potential in pacemaker action potential is due to what?

A

Increase in permeability to Ca2+

28
Q

Calcium channel blockers mainly block what type of channels?

A

L type

29
Q

What effect do calcium channel blockers have on contraction?

A

Decrease force of contraction

30
Q

Other than calcium channel blockers, give a drug which modulates the electrical activity of the heart

A

Cardiac glycosides

31
Q

What effect do cardiac glycosides have on contraction?

A

Increase force of contraction

32
Q

By how many beats/min/degree celsius does the heart increase with increasing temperature?

A

(around) 10 beats/min/degree celsius

33
Q

What is hyperkalaemia?

A

High plasma K+

34
Q

What is hypokalaemia?

A

Low plasma K+

35
Q

What is hypercalcaemia?

A

High plasma Ca2+

36
Q

What is hypocalcaemia?

A

Low plasma Ca2+

37
Q

What do hyperkalaemia and hypokalaemia cause in the heart?

A

Fibrillation and heart block

38
Q

What does hypercalcaemia cause in the heart?

A

Increased heart rate and force of contraction

39
Q

What does hypocalcaemia cause in the heart?

A

Decreased heart rate and force of contraction

40
Q

What cells can reach action potentials and release signals in hyperkalaemia?

A

Non-pacemaker cells

41
Q

What is the only place in the heart where gap junctions are not connecting cells?

A

Annulus fibrosis

42
Q

What is the only route for action potentials between the atria and ventricles?

A

Through the atrioventricular node

43
Q

Action potentials travel through the atrioventricular node very slowly which allows what?

A

The atria to contract and expel blood before the ventricles work

44
Q

What side of the heart has 2 bundle branches?

A

Left

45
Q

What node is the heart’s natural pacemaker?

A

Sinoatrial node

46
Q

An action potential in a single myocyte evokes

A

a very small extracellular electrical potential

47
Q

Lots of small extracellular potentials evoked by many cells de/repolarising at the same time can summate to create

A

large extracellular electrical waves

48
Q

P waves correspond to

A

atrial depolarisation

49
Q

QRS complex corresponds to

A

ventricular depolarisation

50
Q

T wave corresponds to

A

ventricular repolarisation

Cardiovascular System (14 decks)

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