Cardiac Action Potential Flashcards
How does the AP spread in the heart?
SA node -> AV node -> bundle of HIS -> R/L bundle branches -> Purkinje fibers
What are all the pacemaker ability structures from most frequent AP to least?
SA node > AV node > Purkinje fibers
What is overdrive suppression?
-The SA node will fire before the AV or Purkinje fibers reach threshold = therefore controlling HR
What increases the velocity of fibers?
Rank velocities fast to slower
larger diameter = faster
Purkinje > atrial and ventricular m. > AV node
What contract first : the right or left atria?
right
What contracts first endocardium or epicardium?
endocardium
What contracts first: epicardium of the LV or epicardium of the RV?
epicardium of the RV
Where do fast cardiac AP occur?
atria and ventricle myocytes
What occurs during phase 0 of the fast AP?
- depolarization of myocytes via voltage gated Na channels
- L-type Ca2+ channels slow to open
- inward rectifier current (Ik) channels close
What occurs during phase 1 of fast AP?
- rapid partial depolarization due to transient K+ channels
- inactivation gate of Na channel is closed by now
What occurs in phase 2 of the fast AP?
- plateau in membrane potential as there is no net current flow
- plateau due to slow l-type Ca channel rain open
What causes the no net current flow during the plateau phase?
The small influx of calcium is opposed by outward K+ (volt gated) flow of same magnitude
What occurs in phase 3 of the fast AP?
l-type Ca channels close and inward rectifier current opens again to depolarize
What occurs during phase 4 of the fast AP?
- leak channels remain open
- Na volt gate inactivation gate open and activation gate closed
What contributes to the outward current during phase 2 of the fast AP?
K+ volt channels
What processes are occurring that cause phase 2 in the fast AP to occur?
- inward Ca2+ current
- outward K+ current
- inward rectifiers (K+)
What causes the atrial fast AP to be shorter than the ventricular?
- L-type Ca2+ close faster in the atria vs the ventricle
Where does the slow cardiac AP occur?
SA & A V nodes
Purkinje fibers
What occurs during phase 4 of the slow AP?
RMP is gradually reaching threshold due to “funny” Na channels
What occurs during phase 0 of the slow AP?
-depolarization occurs vis Ca2+ voltage gated channels and closure of K+ rectifiers
(causes slow AP)
What occurs during phase 3 of the slow AP?
depolarization via closure of the Ca2+ volt channels and opening of the K+ channels (rectifiers and traditional)
What does overdrive suppression prevent?
-prevents bundle branches and Purkinje fibers from firing spontaneously
Are refractory periods short or long in cardiac cells?
Why?
long, to prevent arrhythmia
What is the absolute refractory period?
no AP can be generated b/c Na volt gate channels are inactivated and will not reopen till reach closer to RMP
What is the relative refractory period?
AP can be generated but requires a greater stimulus or have abnormal conduction
What is the supernormal period?
cell is more excitable that normal and easier to generate AP, may have abnormal conduction
(-70 to -85 mV)
What does chronotropic mean?
- effect changes the HR
- slope in depolarization of slow phase 4 at SA node
What is a positive chronotropic effect?
- HR = faster
- increase in slope of phase 4 (slow)
What is a negative chronotropic effect?
- HR = decrease
- decrease in slope of phase 4 (slow)
What does dromotropic mean?
effect speed of conduction (conduction velocity)
-effect slope of phase 0
What does iontropic mean?
effect strength of muscular contraction
What does lusitropic mean?
effect rate of muscular relaxation
What are the parasympathetic and sympathetic n.s that innervate the heart?
para = vagus
symptoms = cardia splanchnic n.
What structures does the vagus nerve effect on the heart?
What is its NT? receptor?
-SA & AV node
- Acetylcholine
- Muscarinic (M2/M3)
What structures does the cardiac splanchnic n. affect?
What is its NT? receptor?
SA & AV node
- norepinephrine
- beta adrenergic (B1)
What kind of effects does the parasympathetic system have on the heart?
hyperpolarize
negative chronotropic (decrease HR) negative dromotropic (decrease conduction velocity)
-no changes on relaxation or force
What kind of effects does the sympathetic system have on the heart?
“hypopolarize”
postive chronotropic (increase HR)
positive dromotropic (increase conduction velocity)
positive iontropic and lusitropic effects
What channel is responsible to mitigating the effects of the parasympathetic and sympathetic nervous system in regards to K+ flow?
K+ - ACh channels
