CVS-conduction system

Question 1

where is excitation of the heart generated?

Answer 1

SAN

Question 2

where is the SAN located?

Answer 2

right atrium

Question 3

what does excitation generated by the SAN cause?

Answer 3

atria to contract

Question 4

where does the SAN relay the electrical signal to?

Answer 4

AVN

Question 5

where is the AVN located?

Answer 5

within atrioventricular septum

Question 6

what does the AVN do to the impulse and why?

Answer 6

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

Question 7

where does the AVN send the impulse to?

Answer 7

AV bundle (Bundle of His)

Question 8

what is the AV bundle?

Answer 8

continuation of AV node

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

Question 9

where does the AV bundle send impulses to?

Answer 9

purkinje fibres

of right and left ventricles

Question 10

where do purkinje fibres send impulses to?

Answer 10

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

Question 11

what is depolarisation?

Answer 11

inside of cell becomes more positive

Question 12

which channels cause depolarisation?

Answer 12

Na+

Ca2+ (L-type and T-type)

Question 13

what is repolarisation?

Answer 13

when the inside of the cell becomes more negative

Question 14

which channels cause repolarisation?

Answer 14

K+

Question 15

what are gap junctions?

Answer 15

family of proteins between cardiomyocytes that allow the passage of ions

Question 16

what are self propagating action potentials?

Answer 16

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

Question 17

which cells in the heart need to depolarise?

Answer 17

only cells of SAN / AVN

-rest of cardiomyocyte cells follow

Question 18

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

Answer 18

depolarise spontaneously

Question 19

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

Answer 19

• phase 4 (pacemaker potentials)
• phase 0 (depolarisation)
• phase 3 (repolarisation)

Question 20

what is the resting membrane potential of pacemaker cells?

Answer 20

-60mV

Question 21

outline phase 4 of pacemaker cells AP

Answer 21

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

Question 22

which channels are open in phase 4 of pacemaker APs?

Answer 22

• HCN (allow slow Na+ entry)

- T-type Ca2+

Question 23

outline phase 0 of pacemaker cells AP

Answer 23

depolarisation
-L-type Ca channels = influx of Ca

• Faster rate of depolarisation
• HCN channels will deactivate

Question 24

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

Answer 24

• activated=L-type Ca

- deactivated=HCN

Question 25

outline phase 3 of pacemaker cells AP

Answer 25

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

Question 26

which channels open and close for repolarisation of pacemaker cells?

Answer 26

- ca2+ channels close | - K+ channels open

Question 27

is there a plateau phase in pacemaker cells AP?

Answer 27

no

Question 28

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

Answer 28

-90mV

Question 29

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

Answer 29

- phase 4-resting potential - phase 0-rapid depolarisation - phase 1-rapid repolarisation - phase 2-plateau - phase 3-repolarisation

Question 30

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

Answer 30

- maintained by Na/K ATPase pump: 3 Na+ out, 2 K+ in | - membrane more permeable to K+

Question 31

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

Answer 31

open

Question 32

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

Answer 32

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

Question 33

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

Answer 33

inactivated almost immediately

Question 34

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

Answer 34

K+ channels | -cause small depolarisation

Question 35

what causes a plateau phase in non-pacemaker cells?

Answer 35

- 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

Question 36

what occurs in phase 3 of non-pacemaker cells?

Answer 36

repolarisation - Ca2+ channels close - K+ continues to flow out of cell - cycle restarts as membrane becomes more negative

Question 37

what does the P wave of ECG represent?

Answer 37

depolarisation of atria

Question 38

what does the PQ interval of ECG represent?

Answer 38

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

Question 39

what does the QRS wave of ECG represent?

Answer 39

ventricular depolarisation

Question 40

what does the ST segment of ECG represent?

Answer 40

beginning of ventricular repolarisation- should be flat

Question 41

what does the T wave represent?

Answer 41

ventricular repolarisation

Question 42

What phase of cardiomyocyte is early repolarization?

Answer 42

phase 1

Question 43

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

Answer 43

L-Type Channel = faster rate