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Flashcards in Physiology Deck (179)
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1

What is meant by autorhythmicity of the heart?

It is able to generate its own electrical impulses without external stimuli

2

Where does excitation of the heart normally originate?

SA node

3

What are the specialised cells within the SA node that initiate the heart beat called?

Pacemaker cells

4

What is meant by sinus rhythm?

Describes the heart's pace being controlled by the SA node

5

SA node cells have a stable resting membrane potential. True/False?

False
They exhibit spontaneous pacemaker potential

6

What is the function of the spontaneous pacemaker potential?

Takes the membrane potential to threshold (depolarisation) to generate an action potential

7

What gives rise to pacemaker potential?

Decrease in K+ efflux
Slow Na+ influx

8

What causes the rising phase of the action potential (depolarisation) in SA node cells?

Opening of Ca++ channels, resulting in Ca++ influx

9

What causes the falling phase of the action potential (repolarisation) in SA node cells?

Opening of K+ channels, resulting in K+ efflux

10

Summarise the phases of the SA node action potential

Pacemaker potential: decreased K+ efflux, slow Na+ influx
Rising phase: Ca++ influx
Falling phase: K+ efflux

11

Which junctions allow cell-to-cell spread of excitation?

Gap junctions

12

The AV node is the only point of electrical contact between atria and ventricles. True/False?

True

13

AV node cells are large and slow to conduct. True/False?

False
They are small and slow to conduct

14

Why is AV nodal delay present?

To allow time for atrial systole to precede ventricular systole

15

Which fibres enable the excitation to spread to the ventricles?

Bundle of His and Purkinje fibres

16

What gives rise to the rising phase of the action potential in ventricular contractile cells?

Fast Na+ influx

17

Describe Phase 0 of the cardiac action potential

Fast Na+ influx causes reversal of the resting membrane potential from -90mV to +30mV

18

Describe Phase 1 of the cardiac action potential

Closure of Na+ channels + transient K+ efflux causes some repolarisation

19

What gives rise to the plateau phase (phase 2) of the cardiac action potential?

Ca++ influx

20

What gives rise to the falling phase (phase 3) of the cardiac action potential?

K+ efflux

21

Describe Phase 3 of the cardiac action potential

Closure of Ca++ channels and opening of K+ channels allows K+ efflux which causes repolarisation of the membrane potential back to -90mV

22

Sympathetic stimulation causes increased heart rate. True/False?

True

23

What is meant by vagal tone?

Parasympathetic stimulation to the heart dominating in resting conditions

24

The vagus nerve supplies only the SA node. True/False?

False
Supplies both SA and AV nodes

25

What does parasympathetic stimulation do to the AV node?

Increases AV nodal delay

26

Which neurotransmitter acts on which receptor in parasympathetic control of the heart?

ACh on M2 receptors

27

Name a competitive inhibitor of ACh that is used in bradycardia

Atropine

28

Vagal stimulation causes the slope of the pacemaker potential to increase. True/False?

False
Slope decreases (increased AV node delay)

29

What is meant by negative chronotropic effect?

Decreased contraction of the heart due to less frequent action potentials

30

Which areas of the heart does the sympathetic system supply?

SA node
AV node
Myocardium