Cardiac Action Potential And Conduction Flashcards
What is the order of action potential spread in the heart?
SA node —> AV node —> bundle of His —> R/L bundle branches —> purkinje fibers
What will conduct its action potential first,
RA or LA?
RA
What will conduct its action potential first,
Endocardium or Epicardium?
Endocardium
What will conduct its action potential first,
RV epicardium or LV epicardium?
RV epicardium
Is the conduction velocity of the SA node or AV node faster?
SA node ( 1 m/s)
Vs AV = 0.01-0.05 m/s
What generates an action potential most frequently in the heart?
SA node
What is overdrive suppression?
The order in which things will “become” the pacemaker
-SA node then AV node then Purkinje
What determines how fast a cell fiber will be?
How would you order purkinje, atrial & ventricle muscle, and AV node fibers?
Cells w/ fibers of larger diameter = faster
Purkinje > Atrial & ventricular muscle > AV node
What are the cardiac cells that have pacemaker potential?
Sa nodal cells
What will voltage gated sodium channels open?
Abbreviation?
Open during phase 0 and 1
Ina
What will potassium current open?
Abbreviation?
Open during phase 1
Ito
What will L-type Ca channel oepn?
Open during phase 2 and 3
When will the K Chanel open and close?
Clsoed = 2 and 3
Open = helps w/ phase 3
When are the Rpaid and SLow K channels open?
During phase 3
What is the K+ leak channels open ?
Open always
-during phase 2 they would have an increased current outward
What is the Na channel open and closed?
Closed = 4
Open = 3 (during repolarization to help slow depolarization from RMP)
What occurs during Fast Phase 0 ?
In ventricular and atrial myocytes
- voltage gated Na channels open
- transient outward (Ito) potassium current is going out of cell
What occurs during Fast Phase 1?
Initial repolarization in ventricular and atrial myocytes
- Voltage gated Na channels = closed
- voltage gated K channels = open and leaving
What occurs during fast phase 2?
Plateau phase in Ventricular and Atrial Myocytes
- L-type Ca channels = oepn and Ca enters
- voltage gated K = oepn and K leaving
Ca entering/K leaving counters charges and stabilizes membrane potential
What occurs during fast phase 3?
Repolarization in ventricular and atrial myocytes
Ca channels = closed
Voltage gated K = open
Rapid and slow K = open
What occurs during Fast PHase 4?
RMP in ventricular and atrial myocytes
Voltage gated Na, K, Ca = closed
Cell is at normal resting potential = -70–90 mV
What is the inward rectifier current (Ik1)?
Closed during phase 0 (Depolarization)
Helps to stop some of the outward K current to help maintain phase 2 (plateau phase)
Open during phase 3 (to help w/ repolarization)
What occurs in Slow Phase 4?
RMP in SA and AV nodes
Funny Na channel = open
What determines how fast HR will be?
How fast the funny sodium channels open
What occurs in slow Phase 0?
Depolarization in sa and Av noes
-Ca channels = oepn
Ca coming in and is larger than sodium
—> influx is slower and depolarization takes a longer time
What occurs in Slow phase 3?
Repolarization in Sa and AV nodes
- voltage gated K = open
- Ca channels = closed
Why is the SA node the pacemaker?
Bc it has intrinsic, spontaneous depolarization ability via Funny, voltage gated Na channels that open upon complete repolarization of membrane
Why is there a “fast” and “slow” phase?
Bc the slow phase uses Ca in depolarization which is bigger than sodium
—> influx is slower
—> slower to depolarize
(Fast uses Na)
What are refractory periods?
Periods when AP cannot be generated or are generally more difficult to generate
Why are refractory periods longer in cardiac cells?
Help to prevent arrhythmias
What is an Absolute Refractory Period (ARP)?
When no AP can be generated bc voltage gated K channels are closed and unable to open
What is a Relative REfractory Period (RRP)?
AP can be generated but requires greater stimulus and/or have abnormal conduction
What is a Supranormal period (SNP)?
cell is more excitable than normal and easier to general AP
May have abnormal conduction
(Has not fully repolarized yet)
What will happen if the cardiac cells are stimulated during RRP or SNP?
Conduction of AP wil be weaker
What does a Chronotropic effect do?
Changes HR
Slope of depolarization in Phase 4- RMP - at SA node, the funny sodium channels!
What does a Dromotropic effect do?
Effects speed of conduction
Slope of phase 0 - depolarization
What does an Inotropic effect do?
Affects strength of muscular contraction
CHANGES STROKE VOLUME
What does a Lusitropic effect do?
Affects rate of muscular relaxation
What effect will Parasympathetic stimulus have on the the AP?
negative chonotropic effect (lower HR)
Negative dromotropic effect (lower conduction velocity)
What is the N., NTR and R. Of Parasympathetic stimulus to the heart?
CN 10 —> SA and AV nodes
NTR: ACTH
R: Muscarinic (M2/M3)
How does parasympathetic stimulus affect Chronotropy? (2 ways)
- Slower opening of funny Na channels during phase 4
—> takes longer for SA node to reach threshold
—> slower HR - =hypo-polarization of SA node by incr. outward K current via special K channels
How does parasympathetic stimulus affect Dromotropy? (2 ways)
- Reduced inward Ca current
- Increased K+ outward current via special K+ channels
= slower speed of conduction
What does sympathetic stimulus affect chrontropy and dromotropy?
Positive chronotropic effects = increased HR
Positive Dromotropic effects = increases Conduction velocity
Where does Sympathetic stimulus go in the heart?
What is the NTR and r.?
To SA and AV nodes and ventricular myocytes
NTR: NE
R: Beta-1 Adrenergic
How does sympathetic stimulus cause a positive chronotropic effect?
Increases HR by…
- More rapid opening of funny Na channels during phase 4
How does sympathetic stimulus cause positive dromotropic effects?
Will increase speed of conduction by…
- Increased inward Ca++ current
What are the actions of sympathetic and parasympathetic stimulation on HR?
Sympathetic
- Hypo-polarize
- Increased inward Na
Parasympathetic
- Hyper-polarize
- Decreased inward Na
