Changes to the membrane potential Flashcards
Two types of channels
Leakage (always open)
Gated (open when triggered)
In what ways are gated channels gated / triggered
Chemically, mechanically, voltage - gated
What is a graded potential and how far does it travel
An incoming signal (eg. from release of neurotransmitters) over short distances in the dendrites usually
What is an action potential
Signal travelling along an axon
What is a graded potential
A short lived, localised change in membrane potential triggered by the opening of a chemically gated channel (most likely by the release of neurotransmitter by a pre synaptic neuron)
What is a depolarisation and how does it affect the chance of producing an action potential
A decrease in membrane potential by making the inside of the cell less negative. increase the chances of PAAP
on signal
*ASK LECTURER HOW DOES THIS ACTUALLY INCREASE CHANCES OF RAAP
Hyperpolarisation and its effect on action potential production
Increase in action potential making the inside of the cell more negative. decreases the chances of producing an action potential
off signal inhibits ability to do work
Q for lecturer : why are the chances decreased when the separation of charge increases, aka positive ions are more attracted to the increased negative ICF
How does an graded potential work
An active site where the stimulus eg chemical release happens triggers a chemically gated Chanel to open eg. sodium channel, letting sodium into the cell which will be attracted to the negative cell membrane and spread out from the active site. This spread is a current and it’s short-lived and localised
What is an action potential triggered by
Stimulated by a change in voltage across the membrane - sodium or potassium channels (voltage-gated)
Three steps of action potential
Depolarisation (all the way to being positive), repolarisation (back to down to RMP), hyper polarisation (more negative than RMP, like an oops it’s gotten too much momentum and gone too far)
Sodium vs Potassium channel openings
Sodium - closed, open or inactivated (can’t be open again for a period of time)
Potassium - closed or opened
Initial step of action potential
At rest no na or k channels open other than leakage channels due to not enough voltage present to open them
First step of action potential
Depolarisation - graded potential has been received if depolarising, causes membrane potential to become less negative. causes Na channels to open letting Na ions into cell. this influx makes ICF more positive triggers more Na channels to open
What is he threshold point
Point where all sodium channels are open causing huge influx into the cell
What happens if threshold is not reached
An action potential is not created - all or none
Second step of AP
Na channels start to close no more inflow of positive ions at same time K chenille opens and positive K ions outflow. This reestbishes the negative ICF
Third step of AP
Hyperpolarisation - K chennels stay open for too long causing too much K ions to leave the cell making it too negative for a period of time
How does an action potential travel along the axon
Only in one direction, an Na flux causes a current to trigger he threshold of other Na channels Na flows in attracts to negative of membrane travels along etc. etc.
What stops active potential to spread backwards
Inactivation of sodium channels + hyper polarisation (third step)
What is a refractory period and what are the two types
A time during which an action potential can’t be triggered in a neuron
Absolute - goes from time Na channels open to when the inactivation stage of them is complete (enforces one way transmission)
relative - sodium channels are starting to go back to resting state, but due to hyper polarisation it takes a stronger stimulus to reach threshold and trigger an action potential. AP can still be created though, just wth a stronger stimulus
