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FBS2 > Initiation of the heart beat > Flashcards

Initiation of the heart beat Flashcards

1
Q

How does the cardiac action potential differ to the neuronal action potential?

A

It is very long (200ms)

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2
Q

Which ionic movements underly the cardiac action potential?

A

Na+ enters
Ca2+ enters
K+ leaves

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3
Q

What does the cardiac action potential duration depend on?

A

Heart rate

- faster heart rate = shorter AP

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4
Q

What is the cardiac action potential roughly the same as?

A

The QT interval of the ECG

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5
Q

Why is the cardiac action potential so long?

A
  1. Prevents tetany

2. Protects against re-entrant arrythmias

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6
Q

What is the principal pacemaker of the heart (highest intrinsic rate)?

A

SAN

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7
Q

Which specialised conductive tissues conduct the signal from the AVN to the ventricles?

A

Bundle of His -> Purkinje fibres

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8
Q

Which cells show diastolic depolarisation?

A

SAN
AVN
Cells of cardiac conduction system

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9
Q

What is diastolic depolarisation?

A

No stable resting membrane potential

Cells depolarise between beats - ‘clock’ function

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10
Q

Can atrial and ventricular myocytes contract spontaneously?

A

NO - they have stable resting membrane potentials

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11
Q

Describe the cells of the SAN

A

Poorly differentiated
Empty bags - lots of membrane
No cytoplasm
Membranes have pseudopodia

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12
Q

What are the two theories about the ‘clock’ of the heart?

A
  1. Membrane clock - due to changes in ionic currents

2. Calcium clock - due to changes in calcium concentrations

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13
Q

What is the funny current?

A

Inward current (Na and K) that is activated when the membrane is hyperpolarised

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14
Q

Which hormones modify the funny current?

A

Adrenaline stimulates the funny current

Acetylcholine inhibits the funny current

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15
Q

Which drug blocks the funny current and is the only drug that changes HR directly?

A

Ivabradine

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16
Q

Which is more important in the clock theories of cardiac rhythm initiation/

A

Both are important and both modulate each other

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17
Q

What is the function of the ‘AV pause’?

A
  1. Allows time for ventricular filling

2. Prevents transmission of high rates from atria

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18
Q

What speed is conduction from SAN to AVN?

A

Slow

19
Q

What speed is conduction through the ventricular conduction system?

A

Fast - allows apex to contract before base

20
Q

What is the arrangement of the ventricular myocytes?

A

Synctium - ends are interdigitated where the cells meet their neighbours for mechanical strength and for conduction

21
Q

What are the junctions between myocytes called?

A

Intercalated discs (contain gap junctions)

22
Q

What is anisotropic conduction in the heart?

A

Unequal conduction

- electrical impulse travels easier along the fibre than across it

23
Q

What is the cardiac dipole in the ECG?

A

A wave of positiveness followed by a wave of negativeness

From right shoulder to left hip

24
Q

What does the P wave on an ECG represent?

A

Atrial depolarisation

25
Q

What does the Q wave on an ECG represent?

A

Depolarisation of the septum

26
Q

What does the R wave on an ECG represent?

A

Depolarisation of the ventricles (towards apex)

27
Q

What does the S wave on an ECG represent?

A

Depolarisation of the ventricles (towards atria)

28
Q

What does the T wave on an ECG represent?

A

Repolarisation of the ventricles

29
Q

What does the P-Q interval represent?

A

Atrial conduction

example pathology: AV block

30
Q

What does the QRS duration represent?

A

Ventricular conduction velocity

example pathology: Bundle branch block

31
Q

What does the ST segment represent?

A

Heterogeneity of ventricular polarisation

example pathology: MI

32
Q

What does the Q-T interval represent?

A

Ventricular action potential duration

example pathology: long QT syndrome

33
Q

What is the mechanism of cardiac muscle contraction?

A

Calcium induced calcium release

34
Q

Which type of calcium channel is found in T tubules and opens due to voltage changes in membrane?

A

L-type calcium channels

35
Q

What is the mechanism of skeletal muscle contraction?

A

Voltage induced calcium release

36
Q

What is the mechanism of smooth muscle contraction?

A

IP3 induced calcium release

37
Q

Which mechanisms are responsible for calcium removal during relaxation of cardiac muscle?

A

SERCA

Na/Ca exchanger

38
Q

What does a positive chronotrope do?

A

Increases heart rate

39
Q

What does a positive inotrope do?

A

Increase the force of contraction

40
Q

What does a positive lusitrope do?

A

Increase rate of relaxation

41
Q

How do positive chronotropes (e.g. adrenaline) work?

A

Increase funny current

Faster rate of diastolic depolarisation

42
Q

How do negative chronotropes (e.g. acetylcholine) work?

A

Inhibit funny current
Opens KAch channels
Slower diastolic depolarisation

43
Q

How does B1 stimulation of the heart work?

A

B1 adrenoreceptor associated with G protein - works via AC/cAMP/PKA
PKA has many phosphorylation targets

FBS2 (16 decks)

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