Cardiac Action Potentials and Conduction Flashcards
what is the order an action potential spreads in the heart
1) SA node
2) AV node
3) Bundle of His
4) Right/left bundle branch
5) Purkinje fibers
what is the overdrive suppression
it helps maintain order in the contraction of a action potential
this is because SA node, AV node, and Purkinje fibers all can generate their own action potentials
however since SA node is the most frequent it holds the true pacemaker rthym
what fibers/cells have the highest velocity
Velocity is the cells/fibers with the largest diameter conduct the fastest
Purkinje > atrial and ventricular muscle > AV node
what is the order of chambers of contraction as well as epicardium vs endocardium
Right atrium prior to left atrium
Endocardium prior to epicardium
Right ventricle epicardium before left ventricle epicardium
out of the Ventricle, atrium and Sinoatrial node which one has the longest action potential
Ventricle over the atrium
the sinoatrial node has the shortest but its phase 4 will slowly increase to threshold due to its pacemaker capability
Phase, Action and Activated when: INA
Phase: 0,1
Action: open gate
when: THreshold is reached
voltage gated sodium channel
-sodium into cell
Phase, Action and Activated when: Ito
Phase: 1
Action: open
when: cell depolarizes
Very rapid partial repolarization
K+ channel
-K+ out of cell
Phase, Action and Activated when: ICa
Phase: 2 and 3
Action: opens
when: cell depolarizes
Slow to open and remains open for a determined amount of time then closes causing phase 3
L-type Ca channel
-Ca+ into cell
-causes the plateau on AP
Phase, Action and Activated when: IK1
Phase: 2 and 3
Action closes
when: cell depolarizes
inward rectifies, slow to close and remains closed for a determined amount of time then opens helping the phase
Voltage sensing K+ channel
-closed during phase 2 and 3 but opens during phase 0
-prevents too much K+ from leaving
-when open K+ flows out
Phase, Action and Activated when: IKr, IKs
Phase: 3
Action: opens
when: Peak
Contributes to phase 3 repolarization
- Voltage gated K+ channels
- Helps transition 2 to 3
- Allows K+ out of the cell
Phase, Action and Activated when: IK
phase: 4
action: open
when: remain open
K+ leak channels
Open all the time but during phase 2 they have an increased current outward
Phase, Action and Activated when: INaf
phase: 4
action: close
activated: threshold
these contribute to the rise in membrane potential in SA and AV node
Close at threshold but open during repolarization to being the slow depolarization from Resting membrane potential
-creates pacemaker affect
what contributes to the plateauing phase 2 in the ventricle and atrium
Combination of Ca+ current, outward K+ , and inward rectifiers holding back K+
is there a slight delay between action potential and contraction
Yes!!
what is the difference between Phase 0 for SA and AV nodes vs atrium and ventricles
rather than using Na+ voltage gated channels and closure of voltage gated K+ channels to have the quick depolarization
the SA and AV nodes have voltage gated Ca+ channels
what is the difference between Phase 3 for SA and AV nodes vs atrium and ventricles
rather than the opening of voltage gated K+ channels (both rectifiers and traditional)
there is just closure of the voltage gated Ca+ channels
what are the two types of refractory periods
Absolute refractory period (ARP)
-No AP can be generated
Relative Refractory Period (RRP)
-AP can be generated but requires greater stimulus and/or have abnormal conduction
what is the difference in refractory periods for Cardiac Cells
they are much longer, this way it helps prevent arrhythmias
what is the supranormal period
supranormal period (SNP) -is a period where the cell is more excitable than normal and easier to generate AP, may have abnormal conduction
what happens if a cardiac cell is stimulated during RRP or SNP
conduction of that AP will be weaker
Chronotropic
an effect changes in the heart rate, slope of depolarization in phase 4 at SA node
Positive chronotropic effect= faster
Negative chronotropic effect= slower
Dromotropic
effect speed of conduction (conduction velocity) slope of phase 0
usually paired with chronotropic
Inotropic
effect strength of musculature contraction
Lusitropic
effect rate of muscular relaxation
usually paired with Lusitropic
Parasympathetic stimulus on the heart
what are the two effects
receptor
neurotransmitter
to SA and AV node via acetylcholine on a muscarinic receptor (M2/M3)
Negative chronotropic effect:
- slower opening of sodium channels during phase 4
- hyperpolarization of SA node by increasing K+ current via special K+ channels (K+ ACh channel)
Negative dromotropic effects:
- reduce inward Ca+ current
- increase outward K+ churrent via special K+ channels (K+ ACh channel)
Sympathetic stimulus
what are 4 effects
receptor
neurotransmitter
to SA node, AV node and ventricular myocytes via norepinephrine and receptor B1-adrenergic
Positive Chronotropic effects:
-more rapid opening of funny Na+ channels during phase 4
Positive dromotropic effect:
-increased inward Ca+ current
Positive inotropic or lusitropic influence
