CVS-conduction system Flashcards
where is excitation of the heart generated?
SAN
where is the SAN located?
right atrium
what does excitation generated by the SAN cause?
atria to contract
where does the SAN relay the electrical signal to?
AVN
where is the AVN located?
within atrioventricular septum
what does the AVN do to the impulse and why?
delays it-to make sure the atria fully eject blood to ventricles before they contract
where does the AVN send the impulse to?
AV bundle (Bundle of His)
what is the AV bundle?
continuation of AV node
- divides into 2 main bundles:
- –>right bundle branch
- –>left bundle branch
where does the AV bundle send impulses to?
purkinje fibres
of right and left ventricles
where do purkinje fibres send impulses to?
the rest of the cardiac muscle–>causing the ventricles to contract
what is depolarisation?
inside of cell becomes more positive
which channels cause depolarisation?
Na+
Ca2+ (L-type and T-type)
what is repolarisation?
when the inside of the cell becomes more negative
which channels cause repolarisation?
K+
what are gap junctions?
family of proteins between cardiomyocytes that allow the passage of ions
what are self propagating action potentials?
the automatic triggering of neighbouring cells to depolarise (not every cell has to be stimulated for them to depolarise)
which cells in the heart need to depolarise?
only cells of SAN / AVN
-rest of cardiomyocyte cells follow
how do SAN/ AVN pacemaker cells make their action potentials?
depolarise spontaneously
in which order are the phases of in the action potential of pacemaker cells?
- phase 4 (pacemaker potentials)
- phase 0 (depolarisation)
- phase 3 (repolarisation)
what is the resting membrane potential of pacemaker cells?
-60mV
outline phase 4 of pacemaker cells AP
- Activation of HCN channels
- Na+ entry into cell = slow depolarization
- T-type Ca channels open = calcium influx starts
which channels are open in phase 4 of pacemaker APs?
- HCN (allow slow Na+ entry)
- T-type Ca2+
outline phase 0 of pacemaker cells AP
depolarisation
-L-type Ca channels = influx of Ca
- Faster rate of depolarisation
- HCN channels will deactivate
which channels are activated and deactivated in phase 0 of pacemaker cells AP?
- activated=L-type Ca
- deactivated=HCN
outline phase 3 of pacemaker cells AP
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
which channels open and close for repolarisation of pacemaker cells?
- ca2+ channels close
- K+ channels open
is there a plateau phase in pacemaker cells AP?
no
what is the baseline resting potential of non-pacemaker cells?
-90mV
outline the order of phases of action potentials in non-pacemaker cells
- phase 4-resting potential
- phase 0-rapid depolarisation
- phase 1-rapid repolarisation
- phase 2-plateau
- phase 3-repolarisation
how is the resting potential of non-pacemaker cells maintained?
- maintained by Na/K ATPase pump: 3 Na+ out, 2 K+ in
- membrane more permeable to K+
at rest (in non-pacemaker cells) are K+ channels open or closed?
open
which channels open in phase 0 of non-pacemaker cells?
voltage gated Na+ channels open in response to depolarisation
Na+ influx further depolarises cell (positive feedback mechanism)
what happens to Na+ channels at the peak of the AP?
inactivated almost immediately
which channels open in phase 1 of non-pacemaker cells AP?
K+ channels
-cause small depolarisation
what causes a plateau phase in non-pacemaker cells?
- 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
what occurs in phase 3 of non-pacemaker cells?
repolarisation
- Ca2+ channels close
- K+ continues to flow out of cell
- cycle restarts as membrane becomes more negative
what does the P wave of ECG represent?
depolarisation of atria
what does the PQ interval of ECG represent?
time required for AP to travel through SAN, AVN and AV bundle
what does the QRS wave of ECG represent?
ventricular depolarisation
what does the ST segment of ECG represent?
beginning of ventricular repolarisation- should be flat
what does the T wave represent?
ventricular repolarisation
What phase of cardiomyocyte is early repolarization?
phase 1
What channel opens during PHASE 0 of the pacemaker action potential?
L-Type Channel = faster rate
