Conduction Flashcards
(15 cards)
What is the funny current?
sodium and potassium ionic currents allow for a steady increase in the resting membrane potential of the myocyte. Once the threshold potential is reached, an action potential is generated
What are the two unique features of pacemaker cells which serve to initiate sinus activity?
The funny current and calcium-induced calcium release
What is calcium-induced calcium release?
calcium influx through voltage-gated calcium channels causes and increase in intracellular calcium which trigger calcium release from the sarcoplasmic reticulum
What is the main ion responsible for maintaining the resting state?
Potassium through the inward rectifier current (IK1) - the predominant channel open at rest.
Where are the fast response tissues located?
Atria, Bundle of His, Fascicles and bundles branches, terminal Purkinje fibres, Ventricles and AV bypass tracts
Which ions are responsible for the 4 stages of the cardiac AP?
phase 0: Na+ influx
Phase 1:
Which ions are responsible for the 4 stages of the cardiac AP?
phase 0: cell membrane reaches threshold and voltage- gated Na+ channels open - Na+ influx - rapid depolarisation
Phase 1: slowing of Na+ influx + efflux of K+ - depolarisation “notch”
Phase 2: calcium influx balances K+ efflux causing plateau phase
Phase 3: Ca influx ceases and K+ efflux continues with resolution back to the resting potential
What is the function of gap junctions?
low resistance structures that allow ions to flow from one cell to another causing sequential depolarisation from cell to cell - cardiac impulse propagation
How does the action potential in the SA and AV nodes differ from other myocardial cells?
Phase 0 depolarisation depends on influx of Ca (not Na+) via L-type calcium channels and funny channels. This depolarisation occurs more slowly than other myocardial cells
What is the funny current?
Na+ channels which open when the voltage is more negative, immediately after the end of a previous action potential.
This allows for a steady increase in the resting membrane potential of the myocyte until it reaches . threshold potential which triggers the action potential
How do Class 1 antiarrhythmics work, name some.
modulate or block Na+ channels, inhibiting phase 0 depolarisation thereby slowing conduction
1A: intermediate speed of binding and dissociation from receptor
- Quinidine, Procainamide
1B: rapid
- Lidocaine, Mexiletine
1C: slow
- Flecainide, Propafenone
How do class II antiarrhythmics work
inhibit sympathetic activity through beta blockade
- slow the rate of discharge of the sinus node
How do class III antiarrhythmics work, name some.
Block K+ channels thereby prolonging depolarisation
- Sotalol (also beta blocking effect), Amiodarone (also blocks Na+ and Ca channels)
How do class IV antiarrhythmics work, name some.
Calcium channel blockers
- Verapamil - more effect on the SA and AV nodes than Diltiazem
- Dihydropyridines (felodipine, Amlodipine) have few electrophysiologic effects
How do class IV antiarrhythmics work, name some.
Calcium channel blockers
- Verapamil - more effect on the SA and AV nodes than Diltiazem
- Dihydropyridines (felodipine, Amlodipine) have few electrophysiologic effects
- NOTE DILTIAZEM AND VERAPIL DEPRESS LV FUNCTION
