Currents Flashcards
Explain how the pacemaker potential works?
At full hyperpolarisation the funny channel is activated - Decreases K+ Permeability and increases Na+
The Membrane potential slowly rises (aided by opening of some T-type Ca2+ channels) till it hits threshold (~-40mV)
At threshold L-type Ca2+ channels open and the cells rapidly depolarises firing an AP.
At full depolarisation Ca2+ channels close and K+ channels open, an efflux of K+ causes repolarisation.
Explain how the non-pacemaker potential works?
Steady resting membrane potential is maintained by a high resting permeability to K+
Voltage gated Na+ channels open and Na+ floods the cell causes massive depolarisation.
Triggers opening of Ca2+ channels and closing of K+ channels which maintians plateu phase of depolarisation.
Ca2+ channels close and K+ open leading to repolarisation.
How does Temp affect HR?
a rise of 1C = a rise of 10BPM
How does Ivabradine work?
It inhibits the funny channel, slowing the pacemaker potential and so reducing HR
How do CCBs work?
They reduce the amount of Ca2+ allowed into the cell thus reducing force of contraction
How does hyperkalemia affect the heart?
Hyperkalemia
- > Loss of conc. gradient
- > K+ doesnt flow out of cell
- > Cell depolarises on its own
- > Random Contraction
- > Afib and AV block
(Hypokalemia does the same)
How does hypercalcaemia affect the heart?
It increases Contraction strength by increasing calcium available to cell.
Also causes Ca2+ to flood the cell faster leading to a raised HR
