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Cardiovascular > Physiology 1- Origin and Conduction of a Cardiac Impulse > Flashcards

Physiology 1- Origin and Conduction of a Cardiac Impulse Flashcards

1
Q

The electrical signals which control the heart are generated where?

A

Within the pacemaker cells of the sinoatrial node

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2
Q

What is autorhythmicity?

A

No external signals are needed for the heart to beat

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3
Q

Where is the SA node?

A

Right atrium, close to where the SVC enters

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4
Q

A heart beat controlled by the SA node is said to be what?

A

In sinus rhythm

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5
Q

What type of potential do SA node pacemaker cells NOT have, and what type of potential DO they have?

A

Don’t have a resting membrane potential

Do have a spontaneous pacemaker potential

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6
Q

What does the spontaneous membrane potential of pacemaker cells do?

A

Take the membrane potential to a threshold which is required to form an AP

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7
Q

What causes depolarisation in the pacemaker cells?

A

Activation of L-type Ca++ channels and Ca++ influx

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8
Q

What causes hyperpolarisation in pacemaker cells?

A

Inactivation of Ca++ channels and activation of K+ channels causing K+ efflux

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9
Q

What is the pacemaker potential slope (just before depolarisation) in pacemaker cells caused by?

A

K+ efflux
Ca++ influx
Na+/K+ influx (funny current)

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10
Q

How can cardiac excitation spread from the SA node to the AV node?

A

Gap junctions or intermodal pathways

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11
Q

How can cardiac excitation spread from the SA node, through both atria and within ventricles?

A

Cell to cell conduction via gap junctions

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12
Q

What happens at the AV node and why?

A

Impulses get delayed in order to prevent the atria and ventricles contracting at the same time

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13
Q

Where is the AV node located?

A

The base of the right atrium, just above the atrio-ventricular junction

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14
Q

Where do impulses go after passing through the AV node?

A

Through the bundle of His and its left and right branches, then through the Purkinje fibres to spread throughout the ventricles

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15
Q

What is the resting membrane potential in cardiac myocytes before they are excited?

A

-90mV

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16
Q

What causes depolarisation in myocytes?

A

Fast Na+ influx

17
Q

What causes phase 1 of the AP in myocytes?

A

Closure of Na+ channels and K+ efflux

18
Q

What causes phase 2 (plateau phase) of the AP in myocytes?

A

Ca++ influx

19
Q

What cause phase 3 (hyperpolarisation) of the AP in myocytes?

A

Closure of Ca++ channels and K+ efflux

20
Q

What is phase 4 of the AP in myocytes?

A

Resting membrane potential

21
Q

The heart rate is primarily influenced by what?

A

Autonomic nervous system- parasympathetic decreases and sympathetic increases

22
Q

What is the main parasympathetic control to the heart?

A

Vagus nerve

23
Q

What does the vagus nerve do?

A

Continuously influences the SA node- dominates the heart under resting condition

24
Q

What is bradycardia?

A

< 60 bpm

25
Q

What is tachycardia?

A

> 100 bpm

26
Q

How does vagal stimulation slow the heart rate?

A

Through increasing AV node conduction delay

27
Q

What is the neurotransmitter for the parasympathetics to the heart and what receptors does this act on?

A

Acetylcholine acting on M2 muscarinic receptors

28
Q

What is a competitive inhibitor of acetylcholine and when is it used?

A

Atropine- used to speed up the heart rate in severe bradycardia

29
Q

What is a chronotropic effect?

A

Something that affects the heart rate- can be positive or negative

30
Q

What does vagal stimulation on pacemaker cells do to the pacemaker potential?

A

Decreases the slope

31
Q

How do sympathetic nerves increase the heart rate?

A

Decrease the AV nodal delay and increase the force of contraction

32
Q

What is the neurotransmitter for the sympathetics to the heart and what receptors does this act on?

A

Noradrenaline acting on beta1 adrenoceptors

33
Q

What does sympathetic control increasing the heart rate do to the pacemaker potential?

A

Increases the slope

34
Q

What do parasympathetic and sympathetic systems do to the ions involved in action potentials?

A

Sympathetic stimulation decreases K+ efflux and increases Na+/Ca++ influx, parasympathetic does the opposite

Cardiovascular (23 decks)

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