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Cardiovascular > Electrical Properties of the Heart > Flashcards

Electrical Properties of the Heart Flashcards

1
Q

What makes up the intercalated discs in cardiac muscle?

A

Desmosomes and Gap junctions

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2
Q

What are gap junctions?

A

Electrical connection
Narrow channels

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3
Q

What are desmosomes?

A

Physical connection
Stitch cardiac muscle cells together

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4
Q

What does cardiac muscle form?

A

Functional syncytium - independent cells

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5
Q

Explain cardiac muscle and action potentials

A

Has long action potential and long refractory period so cannot exhibit tetanic contraction

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6
Q

How does Ca2+ regulate contraction?

A

Ca2+ from outside cell
Ca2+ release does not saturate troponin so regulation of Ca2+ release can vary the strength of contraction

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7
Q

How does Ca2+ regulate contraction?

A

Ca2+ from outside cell
Ca2+ release does not saturate troponin so regulation of Ca2+ release can vary the strength of contraction

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8
Q

What is a pacemaker cell?

A

Cells that have an unstable resting membrane potential so are spontaneously contracting

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9
Q

What is the normal resting membrane potential of a non-pacemaker?

A

-90mV

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10
Q

Describe the basic electrophysiology of non-pacemaker cells?

A

High resting PK+
Initial depolarisation happens due to increase in PNa+
Plateau is caused by increase of PCa2+ (L-type) and decrease of PK+
Repolarisation is caused by decrease in PCa2+ and increase in PK+

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11
Q

What does L-type mean?

A

Long and large
Stay open longer and large channels causing large depolarisation

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12
Q

Describe pacemaker action potential

A

Action potential - increase in PCa2+ (L-type)
Pacemaker potential - gradual decrease in PK+, early increase in PNa+ (If) and late increase in PCa2+ (T-type)

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13
Q

What does Ca2+ T-type mean?

A

Tiny and transient
Don’t let a lot of Ca2+ into cell and don’t sty open long

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14
Q

Describe the sinoatrial node

A

Fastest pacemakers are here so depolarise to threshold first - 0.5m/s
Wave of depolarisation in atrium which leads to atria contracting and squeezing blood into ventricle

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15
Q

Describe the annulus fibrosis

A

Ring of non-conducting tissue which prevents depolarisation immediately form atrium to ventricle

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16
Q

Describe the atrioventricular node

A

Conducts slowly - 0.05m/s
Acts as a delay box so atria have time to depolarise and contract before ventricle

17
Q

Describe the bundle of His and Purkinje fibres

A

Rapid conducting system - 5m/s
Ensure coordinated contraction of the heart

18
Q

Describe an AP in a single myocyte

A

It evokes a very small extracellular electrical potential

19
Q

Describe what happens when lots of small extracellular electrical potentials are evoked?

A

Due to many cells depolarising and repolarising at same time
Can summate to create large extracellular electrical waves
This can be recorded in periphery by electrocardiogram

20
Q

What does the P wave represent on ECG?

A

Atrial depolarisation

21
Q

What does the QRS complex represent on ECG?

A

Ventricular depolarisation

22
Q

What does T wave represent on ECG?

A

Ventricular repolarisation

23
Q

What is the U wave on an ECG?

A
24
Q

Why cant atrial repolarisation be seen on ECG?

A

Atrial repolarisation gets lost by QRS complex as happen at same time and QRS complex is bigger

25
Q

What is the RR interval?

A

Between the R intervals
Can measure heart rate manually
Large square is 0.2

26
Q

Describe first degree heart block on an ECG?

A

PR interval is increased
Disruption of conduction of depolarisation to AV node onto ventricles

27
Q

Describe 2nd degree heart block

A

QRS drops as the P interval increases
Some failure of conduction

28
Q

Describe 3rd degree heart block

A

QRS is seen because pacemaker take over and cause contraction
No AV conduction - depolarisation not getting to ventricles

29
Q

Describe atrial flutter

A

Atria conduct faster than they should
Lots of p waves before QRS

30
Q

Describe atrial fibrillation

A

Failure of pacemaker spread of wave of depolarisation to atria
Cell are contracting and depolarising at different times so uncoordinated

31
Q

Describe ventricular fibrillation

A

Uncoordinated contraction of ventricles and means heart not pumping blood effectively
Not getting to brain so can cause unconsciousness

Cardiovascular (33 decks)

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