Ventricular Ap Flashcards
Which 2 major ions are in highest concentration outside
Na and ca (ca inside but in sr)
What is phase 4 (start and end of ap)
Rmp at -80mv
Cell is polarised
What is the major channel in phase 4 rmp
Na/k ATPase
What is phase 0
Depolarisation via fast acting Na channels eg scn5a
What happens to allow Na in through fast acting Na channels
Electrical impulse from neighbour myocytes causes conformational change
What happens at around +40mv
Fast acting Na channels rapidly close via conformational change (h gate active)
What is phase 1
Early repolarisation
Transient outward current flow
via fast opening k channels (ones that encode ikr)
Is transient outward current flow in early repolarisation down conc gradient
Yes
Why does repolarisation stops fast after phase 1
Plateau phase phase 2 starts when ca enter cell
What type of ca channel allows entrance into cell in phase 2 plateau
L type (long type)
What does ca enterance allow
Excitation contraction coupling
Ca induced ca release via Ryanodine receptors on sr
Which phase is unique to ventricular heart muscle and why
Phase 2, ca not needed for others bc eg san cells don’t contract
Which channels causes uptake of ca back into sr
Ca ATPase
Serca channel
Other than serca, what else removes ca for heart relaxation (diastole)
Ncx
3 Na move in , 1 ca moves out via energy from Na gradient
What is phase 3
Rapid repolarisation
L type channel closes
Slow acting k channels open eg kcnq1
K leaves cell
(Shortly after restored by Na/k pump)!
How is san cell ap different
No phase 1 or 2 (just phase 0 dep and 3 rep)
Uses ca for depolarisation mainly
Has an unstable rmp
What is diff about the rmp in san compared to ventricular myocytes
Not stable, it gradually diminishes to reach threshold
Usually less negative eg -70
What is the name of the unstable rmp
Pacemaker potential
What is the unstable pacemaker potential reason called
Funny current - opening of Na or k channels to get it closer to threshold
What allows pacemaker to reach threshold
SNS release of nadr which makes it less negative
PNS allows k permeability so it becomes more repolarised= bradycardia
Which 2 arrhythmias are normal to have eg through exercise or rest
Sinus tachycardia and bradycardia
Heart rate slows through san but conduction is normal through heart
What is sinus tachycardia and bradycardia influenced by in san
The Ans
What are the 3 causes of arrhythmia
Abnormal impulse formation (eg early or late repolarisation or depolarisation)
Enhanced automaticity - increased SNS activity causes extra heart beats
Re entry mechanisms - current through abnormal pathways
