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Cardiology > Origin and conduction of cardia impulse > Flashcards

Origin and conduction of cardia impulse Flashcards

1
Q

How is the heart controlled?

A

The heart is electrically controlled by signals generated within the heart

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2
Q

What is the term to describe the heart and its ability to pump in the absence of external stimuli?

A

Autorhythmicity

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3
Q

Where in the heart does the excitation normally originate?

A

The Sino-Atrial (SA) node (the pacemakers)

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4
Q

Where is the SA node located?

A

In the upper right atrium close to where the SVC enters the right atrium

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5
Q

What is the function of the SA node (in a general sense)? and what term is given to this?

A

Sets the pace for the entire heart.

Termed sinus rhythm

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6
Q

What do cells in the SA node not have?

A

A RMP

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7
Q

What kind of potential does the SA exhibit?

A

Spontaneous pacemaker potential (slow depolarisation of MP to a threshold)

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8
Q

What does the pacemaker potential do?

A

Takes the MP to a threshold to generate an AP in the SA nodal cells

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9
Q

Describe the basic ionic flux for the spontaneous pacemaker potential

A

Decrease in K+ efflux
Na+ and K+ influx (Funny current)
Transient Ca++ influx (via T-type Ca++ Ch’s)

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10
Q

What happens when the threshold has been reached for a pacemaker action potential?

A

The rising phase - activation of L-type Calcium channels resulting in an influx of calcium.

The falling phase - is cause by the inactivation of L-type calcium channels and activation of potassium channels (efflux of potassium)

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11
Q

What type of calcium channels are involved in spontaneous pacemaker potential?

A

T-Type channels - transient calcium influx

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12
Q

What type of calcium channels are involved in the pacemaker action potential?

A

L-Type Calcium channels

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13
Q

Summarise the SA node cell action potential

A
  1. Decrease in K+ efflux
  2. Funny current influx (Na+ and K+ influx)
  3. Transient Ca2+ influx (T-Type Calcium channels)

All of the above is spontaneous until the pacemaker action potential threshold has been reached. Then:
L-type calcium channels open allowing an influx of calcium (depolarisation) and re-polarisation and is K+ efflux

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14
Q

Anatomically, describe the pathway of excitation within the heart.

A

Begins at the SA node (cell-cell conduction) - AV node - Bundle of the His - purkinje fibres - ventricle mass cells

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15
Q

What cell feature allow for the excitation to be spread from the SA node to the ventricles?

A

From the SA node - AV node through both atria to the ventricles via gap junctions which all for a cell to cell current flow.

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16
Q

Where is the AV node located?

A

At the base of the right atrium, above the junction of the atria and the ventricles

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17
Q

Do the AV node cells have a fast or slow conductivity?

A

SLOW conduction velocity

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18
Q

How does excitation pass from the SA to AV node?

A

Cell-cell junctions via gap junctions

Some inter-nodal pathways

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19
Q

Why is the conduction delayed within the AV node?

A

To allow for atrial systole (contraction) which precedes ventricular systole

20
Q

From the AV node how is the excitation conducted to the ventricles?

A

Via the Bundle of His and Purkinje fibres (Right and left branches)

21
Q

Is the conduction from AV node to the ventricles slow or rapid?

22
Q

What is TMP (transmembrane potential) of a pacemaker action potential

23
Q

What is the RMP in atrial and ventricular myocytes (contractile cardiac cells)?

A

-90mV (different from the pacemaker cells) and it remains here until the cell is excited

24
Q

What ion influx causes the depolarisation rising phase of the contractile cardiac muscle cells?

A

Na+ (fast influx)

25
What MP does the rising phase in cardiac contractile AP reach?
+20mV
26
What is phase 0?
Phase 0 is the rising phase of contractile cardiac muscle cells to +20mV due to a rapid influx of Na+ ions.
27
How many phases are there in Ventricular muscle action potential and describe which ion (and associated flux direction) at each phase
5 - Phase 0, 1, 2 ,3 and 4. Phase 0 - is the influx of Na+ ions Phase 1 - is the opening of K+ channels and the transient efflux of K+ ions Phase 2 - Ca2+ influx Phase 3 - Closure of the Ca2+ channels and K+ efflux Phase 4 - RMP
28
Describe the plateau phase (around phase 2 of the AP) of the ventricular action potential
Where the AP is maintained after the peak of the AP - unique to cardiac muscle cells
29
What ion causes the plateau phase of the Ventricular contractile cardiac AP?
The influx of Ca2+ ions through L-type Ca2+ ion channels
30
What happens during the falling phase of a ventricular muscle action potential?
K+ channels open | Ca2+ are inactivated
31
What changes the heart rate?
Done so by the autonomic nervous system Sympathetic stimulation increases the heart rate Parasympathetic stimulation decreases the heart rate
32
Which nerve gives the parasympathetic supply the heart? (Under normal resting conditions)
The Vagus - cranial nerve X - slows the intrinsic HR from ~ 100bpm to a normal resting HR of ~ 70 bpm
33
What is a normal resting HR (in BPM)
60-100
34
Bradycardia
less than 60 BPM
35
Tachycardia
More than 100 BPM
36
Parasympathetic supply to the heart is to the ______ and ________ (2)
SA and AV node
37
Parasympathetic - What does vagal stimulation do?
Slows the heart rate and increases the AV node delay
38
What is the parasympathetic NT? And to which receptors do they act upon?
ACh | Muscarinic M2 receptors
39
Parasympathetic: Name a competitive inhibitor of ACh & when it's used
Atropine - severe cases of bradycardia to speed up the heart
40
What are the effects of vagal stimulation on pacemaker potentials?
Cell hyperpolarises - takes longer to reach threshold The slope of the pacemaker potential decreases frequency of the AP increases NEGATIVE CHRONOTROPIC EFFECT (decreases the heart rate)
41
Sympathetic supply to the heart is to the ______, ______ and ________ (3)
SA node, AV node and myocardium
42
What does cardiac sympathetic stimulation do to the heart rate and AV node?
Increases HR Decreases AV nodal delay increases the force of contraction
43
Sympathetic: What is the NT and which receptors does it act upon?
NA - B1 adrenoreceptors
44
NA on pacemaker cells:
Slope of pacemaker potential increases pacemaker potential reaches threshold quicker frequency of AP's increase (+ chronotropic effect)
45
What is positive chronotropic effect?
Increase in heart rate
46
What does an ECG record?
The depolarisation and re-polarisation cycle of cardiac muscle. This is obtained from the skin surface.
47
How many standard limb leads are there?
3: Lead I: Right Arm to Left Arm Lead II: Right Arm to Left Leg Lead III: Left Arm to Left leg

Cardiology (2 decks)

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