Cardiac action potenitals Flashcards
(22 cards)
What is electrophysiology?
The study of electrical properties of biological cells and tissues
What is the resting membrane potential?
The voltage difference across the plasma membrane
What is the average resting membrane potential of a cardiomyocyte?
-90 - -80mV
What determines resting membrane potential?
Combination of electrochemical gradients
Is the inside of the membrane positive or negative compared to the outside?
Negative
Does K+ move into or out of the cell?
Out
Do Na+ move into or out of cell?
In
How is the resting membrane potential maintained?
All channels closed except some K+ channels allowing some K+ to leak out of the cell
How does depolarisation occur?
Na+ channels open and Na+ move into the cell. more voltage gated Na+ ion channels open and depolarisation occurs
What occurs during early repolarisation?
Na+ channels close.
K+ leaks out of the cell causing small repolarisation
What occurs during the plateau phase?
Voltage gated L-type Ca2+ channels open and Ca2+ floods into the cell - this is balanced by the K+ leaving the cell so it plateaus
What occurs in the muscle during plateau phase?
Ca2+ moves into the cell and causes sarcoplasmic reticulum to release more Ca2+ and contraction occurs
How does repolarisation occur?
Ca2+ channels close and voltage gated K+ channels open. K+ leaves the cell and causes repolarisation
How is the resting membrane re-established after the action potential?
2K+ in exchanged for 3Na+ out.
When re-established all channels close except leaky K+ channels
When does the depolarisation stage occur in relation to the increase in pressure in the ventricle?
Just before the increase in the pressure
What are the differences between contractile myocardium AP and pacemaking cell AP?
Pacemaking cell does not have a constant resting membrane potential
Depolarisation caused by Ca2+ not Na+
No plateau
Higher permeability of Ca2+
Why is the resting membrane potential of pacemaking cell not constant?
Hyperpolarisation and cyclic nucleotide gated channels are not specific so allow Na+ and Ca2+ into the cell.
Causes resting potential to increase
How does depolarisation occur in pacemaking cells?
T-type Ca2+ channels cause slow depolarisation before threshold (along with some leaking Na+)
T-type Ca2+ channels stimulate L-type Ca2+ channels.
L-type Ca2+ channels cause most depolarisation
How does repolarisation occur in pacemaking cells?
K+ moving out of the cell
What ion mainly contributes to depolarisation in myocytes?
Na+
What ions contribute to plateau phase in myocytes?
Ca2+ and K+
What channels contribute to pacemaking cells in cardiomyocytes?
Hyperpolarsiation and cyclic nucleotide gated channels
T-type and L-type Ca2+
