electrical cycle of heart Flashcards
where is the bundle of his
left & right Branches run down ventricular septum to apex
where are purkinje fibres
Located throughout ventricular myocardium from apex to base
what controls the rate of prodution of action potentials by the SA node
how fast Na+ leaks through funny channels (HCN channels)
If more HCN channels are open, Na+ leaks in faster, reaching the threshold for activating voltagedependent Ca2+ channels more quickly and shortening the distance between action potentials
what a HCN channel
Hyperpolarizationactivated cyclic nucleotide–gated (HCN) channels)
what are the steps of electrical conduction in the heart
- SA node depolarizes
- electricl activity goes rapidly to AV node via internodal pathways
- depolarization speads slowly across atria. Conduction slows through AV node
- depolarization moves rapidly through ventricular conducting system to apex of heart
- depolarization wave spreads upward from the apex
describe phase 0 of ventricular action potential (rapid depolarization)
stimulus depolarizes cell membrane to -70mV
At -70mV, Na+ channels are activated and allow inward current, current peaks the membrane potential at +47mV
describe phase 1 of the ventricular action potential (early repolarization)
the increase in potential, results in opening of outward K+ channles and inward Ca+ channels.
repolarization from +47mV to +10mV due to rapid closure of I and activation of outward K+
describe stage 2 of the ventricular action potential (action potential plateau)
membrane potential remains depolarized near 0mV
plateau phase is maintained by two inward Ca+ channels and four outward k+ currents
describe stage 3 of the ventricular action potential (final rapid repolarization)
inward currents inactivate
k+ currents dominate and cause rapid repolarization
describe stage 4 of the ventricular action potential (resting membrane depolarization and diastolic depolarization)
outward K+ channles deactivate
membrane is repolarized to -40mV
inward channles continue to drive membrane potential to -70mV and the voltage dependent Na+ channel which causes phase 0 remians inactive
what is an ECG useful for
Assessment of orientation of the heart
Localisation of areas that do not
conduct electrical activity normally
Assessment of myocardial
hypertrophy or atrophy
where is the SA node
within right atrial wall at junction with superior vena cava
where is the AV node
above cardiac septum at junction of atria & ventricles
Draw a graph showing the action potential in the heart
slides 3 A
