Ionic currents Flashcards
How can we assess the rate of different parts of the heart?
Make a ligature between 2 sections
What part of the heart initiates the heart beat?
SA Node, in the right atrium
What are the 3 internodal tracts?
They are the paths by which AP propagates in right atrium from SA node to the AV node
- Anterior tract
- Middle tract
- Posterior tract
How does the contraction from SA node propagates to the left atrium?
Anterior tract gives rise to trapezoid shaped bundle of fibres, goes through interatrial sulcus from right to left atrium called Bachmann’s bundle
What is the order of propagation after the AV node?
- Bundle of His
- 2 bundle branches
- Purkinje fibers
What are the different parts of the SA node?
- Leading pacemaker site
- P cells (primary pacemaker cells)
- Crystal terminalis = muscle in myocardium of RA, extends between SVC and IVC
- Transitional cells = transmit electrical impulse from SA node → right atrium
*Conduction slower in the leading pacemake site and accelerates as we get farther
What are the types of connective cells in the SA node, in the atrium and in ventricles?
SA node → Cx40 and Cx45
Atrium and ventricles → Cx43
*higher # = better coupled, more conductive
What is the name of the connective tissue separating the right atrium and right ventricle?
Tendon of Todaro (not conducting)
What is the triangle of Koch?
Tendon of Todar + Tricuspid annulus + coronary sinus (CS)
Region wherethe AV node is
What is the approximated duration of an AP in the heart vs in muscle tissues?
heart ~ 100ms
muscles ~ 1ms
Which tissues have fast vs slow type action potentials?
Fast: Atrium muscle, Purkinje fibers, Ventricular muscle
Slow: SA node, AV node
What are the different phases of the cardiac action potential?
0 - Upstroke (Greater upstroke = greater conduction)
1 - Early repolarization
2 - Plateau
3 - Repolarization
4 - Resting potential
How is phase 4 of the heart action potential called and characterised in the SA node?
diastollic depolarization: potential goes from maxiaml diastollic potential → threhold potential
How long is approximately the Absolute Refreactory Period (ARP) and Aelative Refractory Period (RRP) for an atrial AP?
ARP ~ 200 ms
RRP ~ 70 ms
How are the cardiac muscle (CM) AP different from the skeletal muscle (SM) AP?
- Long APD in CM prevents them from being tetanized
- CM contraction controlled by APD vs SM force regulated by recruitment
- CM Ca influx → Ca release vs SM depolarization → contraction
What are the intracellular and extracellular concentrations of ions in the heart ?
Na+ extra = 140 mM, intra = 14 mM
K+ extra = 4 mM, intra = 140 mM
Ca++ extra = 2.5, intra = 0.0001
What is the Nernst equation?
E = -61.5 log ( [Conc. i]/[Conc o] )
How does extracellular K+ affect fast type ventricular AP?
- Depolarization of resting potential
- Decrease AP upstroke velocity, faster repolarization
What is the relationship between External [K+] and Vm?
At higher external [K+], it get closer to NERNST prediction of K+ equilibrium