Action potential Flashcards
How is the membrane potential created?
There is an K+/Na+ ATP pump that pumps 2K+ ions into the cell and three Na+ out of the cell. There are also ion channels specific for potassium. This concludes in a concentration gradient driving the potassium out of the cell and an electrostatic force dragging the K into the cell when the K+ leaves. This will lead to an equilibirum and all the ions in and out of the cell also drawn in and out of the cell due to pumps, ion channels, wanting to follow the concentration gradient and the electrostatic forces makes the mebrane potential at around -70mV
What is the equilibirum potential?
Every ion has it’s own equilibirum potential which through Nernst equation tells us how much of the ions can be found inside and outside of the cell.
What ion channels triggers are there?
Mechanical sensitive ion channels that is triggered by membrane stretch, ligands (that is triggered by hormones and neruotransitters), temperature and voltage sensitive ion channels.
Describe how the ion channels open and close mechanism function and how they differ for different ions
The open and close part of the ion channel is positivly charged so when there is a negative voltage inside the mebrane the ion channel is closed because the positive charged is attracted to the negative. If the inside of the cell becomes positive the ion channel will be repulsed and open by instead pushing outwards of the cell where there is a more negative charge. They can also be inactivated with a so called ball and chain mechanism. Different ion channels are faster and slower, some are almost always open some go from inactivated to active very slowly.
Describe the ion channel structure
They are all tetrameres. Inside there is a ion sensitive filter and surronding it there is 4 voltage sensed domains that sense the memrbane voltage. The voltage sensed domains can be futher divided into 4 subuniths in each domain. Then there are also 2 segments that build up the pore domain.
Describe the ation potential
Hodgkins cycle describe the positive feedback that triggers such a fast depolarization. There is first an increase in Nap, permability for sodium by sodium channels opening whih leads to an influx of Na+. Through the positive feedback system this will lead to membrane depolarization, the membrane becomes more positive opening more sodium channels and the cycle goes on creating a fast curve.
Describe the depolrization system
After some time the sodium channels inactivate and the potassium channels open. Since the concentration gradient is so stable since it’s in mole theres so many ions in and out it doesn’t really change the concentration gradient the ions are driven by electrical forces. The potassium channels therefore open because of the positive charge inside the cell and it will take some time to close again. So sodium stops coming into the cell and potassium starts leaving the cell causing a hyperolarization which leads to an even more negative charge for a while until it stabilizes,.
