Electrical Excitability Flashcards
What is an action potential?
This is a change in potential across a membrane and is dependent on membrane permeability and ionic gradients.
What type of response can an action potential be described as?
All or nothing. If it reaches threshold then an action potential will be fired.
What can be said about action potentials in different locations?
They all differ slightly in shape as well as in amplitude.
In an axon, what ion channels are responsible for an action potential?
Firstly, Na channels open and this leads to influx of sodium which depolarises the membrane. These become inactivated and then K+ channels open and the membrane repolarises.
What is the effect of decreasing Extracellular Na on the amplitude of an action potential?
It will cause a great reduction because there is a much lower concentration gradient. It will also be a much smoother curve as there will not be a sudden influx of sodium.
How can we increases conductance of a particular ion for the membrane? What effect does this have on membrane potential?
Have more of the ion channels open. This leads to the membrane potential moving closer to the equilibrium potential for that ion.
What is the use of voltage clamping?
This is where a current is passed between two electrodes thus controlling membrane potential and allowing us to investigate different channels within the membrane.
What change can occur to the membrane potential that increases the rate of influx of sodium?
If the cell is more depolarised the sodium influx is faster.
What determines of an action potential is fired in an axon?
Action potentials are initiated at the axon hillock. If the depolarisation is sufficient to take the cell to threshold then an action potential will be fired.
In the upstroke of an AP, what type of feedback occurs?
Positive feedback. The Na channels open which causes the membrane to depolarise which causes more sodium channels to open.
Describe what is happening in the downstroke of the action potential.
Sodium channels become inactivated, and potassium channels open leading to potassium efflux and Repolarisation of the membrane.
What is the absolute refractory period?
This is the time during and after an action potential in which the majority of sodium channels are inactivated and so it is not possible for another action potential to be fired.
What is the relative refractory period?
This is when sodium channels are recovering and excitability is returning to normal as the number of inactivated sodium channels decreases.
What is needed for sodium channels to move from the inactivated state to the closed state?
Hyperpolarisation
What is accommodation?
This is where if there are many successive action potentials, the threshold needed to fire an action potential increases and becomes more positive due to the inactivation of sodium channels. It is possible in this circumstance for threshold to be exceeded without the firing of an action potential.
