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Medicine yr1 > CVS-conduction system > Flashcards

CVS-conduction system Flashcards

1
Q

where is excitation of the heart generated?

A

SAN

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2
Q

where is the SAN located?

A

right atrium

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3
Q

what does excitation generated by the SAN cause?

A

atria to contract

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4
Q

where does the SAN relay the electrical signal to?

A

AVN

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5
Q

where is the AVN located?

A

within atrioventricular septum

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6
Q

what does the AVN do to the impulse and why?

A

delays it-to make sure the atria fully eject blood to ventricles before they contract

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7
Q

where does the AVN send the impulse to?

A

AV bundle (Bundle of His)

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8
Q

what is the AV bundle?

A

continuation of AV node

  • divides into 2 main bundles:
  • –>right bundle branch
  • –>left bundle branch
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9
Q

where does the AV bundle send impulses to?

A

purkinje fibres

of right and left ventricles

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10
Q

where do purkinje fibres send impulses to?

A

the rest of the cardiac muscle–>causing the ventricles to contract

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11
Q

what is depolarisation?

A

inside of cell becomes more positive

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12
Q

which channels cause depolarisation?

A

Na+

Ca2+ (L-type and T-type)

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13
Q

what is repolarisation?

A

when the inside of the cell becomes more negative

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14
Q

which channels cause repolarisation?

A

K+

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15
Q

what are gap junctions?

A

family of proteins between cardiomyocytes that allow the passage of ions

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16
Q

what are self propagating action potentials?

A

the automatic triggering of neighbouring cells to depolarise (not every cell has to be stimulated for them to depolarise)

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17
Q

which cells in the heart need to depolarise?

A

only cells of SAN / AVN

-rest of cardiomyocyte cells follow

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18
Q

how do SAN/ AVN pacemaker cells make their action potentials?

A

depolarise spontaneously

19
Q

in which order are the phases of in the action potential of pacemaker cells?

A
  • phase 4 (pacemaker potentials)
  • phase 0 (depolarisation)
  • phase 3 (repolarisation)
20
Q

what is the resting membrane potential of pacemaker cells?

A

-60mV

21
Q

outline phase 4 of pacemaker cells AP

A
  • Activation of HCN channels
  • Na+ entry into cell = slow depolarization
  • T-type Ca channels open = calcium influx starts
22
Q

which channels are open in phase 4 of pacemaker APs?

A
  • HCN (allow slow Na+ entry)

- T-type Ca2+

23
Q

outline phase 0 of pacemaker cells AP

A

depolarisation
-L-type Ca channels = influx of Ca

  • Faster rate of depolarisation
  • HCN channels will deactivate
24
Q

which channels are activated and deactivated in phase 0 of pacemaker cells AP?

A
  • activated=L-type Ca

- deactivated=HCN

25
Q

outline phase 3 of pacemaker cells AP

A

repolarisation

  • Peak of action potential = Ca2+ channels inactivate, K+ channels open
  • K+ move out of cell TMP = -60mV
  • Membrane must be negative again for HCN to open again for another AP
26
Q

which channels open and close for repolarisation of pacemaker cells?

A
  • ca2+ channels close

- K+ channels open

27
Q

is there a plateau phase in pacemaker cells AP?

A

no

28
Q

what is the baseline resting potential of non-pacemaker cells?

A

-90mV

29
Q

outline the order of phases of action potentials in non-pacemaker cells

A
  • phase 4-resting potential
  • phase 0-rapid depolarisation
  • phase 1-rapid repolarisation
  • phase 2-plateau
  • phase 3-repolarisation
30
Q

how is the resting potential of non-pacemaker cells maintained?

A
  • maintained by Na/K ATPase pump: 3 Na+ out, 2 K+ in

- membrane more permeable to K+

31
Q

at rest (in non-pacemaker cells) are K+ channels open or closed?

A

open

32
Q

which channels open in phase 0 of non-pacemaker cells?

A

voltage gated Na+ channels open in response to depolarisation
Na+ influx further depolarises cell (positive feedback mechanism)

33
Q

what happens to Na+ channels at the peak of the AP?

A

inactivated almost immediately

34
Q

which channels open in phase 1 of non-pacemaker cells AP?

A

K+ channels

-cause small depolarisation

35
Q

what causes a plateau phase in non-pacemaker cells?

A
  • L-type Ca2+ channels open, they then slowly inactivate as potassium current increases in activity
  • sustained plateau of calcium moving into cell & potassium moving out of cell
  • muscle excitation-contraction coupling
36
Q

what occurs in phase 3 of non-pacemaker cells?

A

repolarisation

  • Ca2+ channels close
  • K+ continues to flow out of cell
  • cycle restarts as membrane becomes more negative
37
Q

what does the P wave of ECG represent?

A

depolarisation of atria

38
Q

what does the PQ interval of ECG represent?

A

time required for AP to travel through SAN, AVN and AV bundle

39
Q

what does the QRS wave of ECG represent?

A

ventricular depolarisation

40
Q

what does the ST segment of ECG represent?

A

beginning of ventricular repolarisation- should be flat

41
Q

what does the T wave represent?

A

ventricular repolarisation

42
Q

What phase of cardiomyocyte is early repolarization?

A

phase 1

43
Q

What channel opens during PHASE 0 of the pacemaker action potential?

A

L-Type Channel = faster rate

Medicine yr1 (55 decks)

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