ionic basis of the action potential (week 8 lecture 2) Flashcards
which ions are cell membranes most permeable to AT REST due to membrane proteins?
potassium ions (only a small number of potassium ions move out of the cell by diffusion, down the chemical gradient)
what membrane potential does the movement of potassium ions out of the cell result in?
a negative membrane potential (negative inside the cell)
why does only a small number of potassium ions diffuse out of the cell?
the diffusion of potassium out of the cell generates a negative membrane potential which prevents any more positive potassium ions diffusing out of the cell. (the electrical potential balances the chemical gradient of potassium)
what membrane potential does the movement of a small amount of sodium ions into the cell cause?
a positive one. (this is a less significant movement because AT REST the cell membrane is 50 times less permeable to sodium ions)
how can the membrane potential be measure?
by conducting an experiment by injecting current into a cell and using an oscilloscope. (the equation V=IR is used to calculate voltage)
what is the resting membrane potential of an excitable cell?
between -60 and -80mV
what is depolarisation?
when the membrane potential suddenly becomes positive
what is repolarisation?
when the membrane potential returns to the resting membrane potential after depolarisation.
what is hyper polarisation?
when the membrane potential becomes more negative (e.g. when chloride ions move into the cell)
what is the difference between the way an excitable cell reacts to injected current and the way an unexcitable cell reacts?
in excitable cells, the membrane potential increases until reaches a threshold potential at which point it increases rapidly then decreases rapidly.
when does the membrane potential peak in an action potential?
around +30mV
what happens after an action potential has reached the peak?
it repolarises until it returns to the resting level (it actually overshoots to be closer to the resting membrane potential of potassium).
what happens to the sodium channels when the membrane potential reaches the threshold?
there is a rapid opening of of sodium channels (at the activation gate) which results in a massive and rapid influx of sodium ions resulting in a great increase in the membrane potential (+30mV). There is then a slow coming of the inactivation gate and no more sodium ions enter the cell.
what happens to the potassium ion channels during the action potential?
there is a delayed opening of the potassium ion channels at the threshold at the peak membrane potential. This results in a large amount of potassium ions leaving the cell which results in a rapid decrease of the membrane potential to hyper polarisation (about -80mV)
what is the ratio of sodium permeability to potassium permeability of the membrane at rest?
1/50
