Week 1- Part 5- Postsynaptic potentials (EPSPs and IPSPs). Flashcards
What do we technically call what excites a neuron?
What does whether or not a neuron fires depend on?
A postsynaptic potential.
Depends on if it gets sufficiently stimulated- can be stimulated by multiple inputs.
What matters?
What can one neuron do to another one?
Whether the threshold of excitation is reached in the region of the axon hillock.
Stimulate it- depolarizing the membrane slightly in the other- but it might not do it enough to make the neuron fire- it might only fire if stimulated by two neurons at once.
But what excites a neuron (triggers an action potential):
What does excitation =?
What causes this depolarisation?
To understand why, what do you need to look at?
Excitation = depolarization of membrane in region of axon hillock, so that the threshold is reached.
The action of neurotransmitters.
Need to look at a different type of ion channel.
What can other channels do?
What is a ligand?
How is it normally?
What can ligands be?
What can this do?
Open or close depending on if something binds to them- called a ligand gated ion channel.
The name for a molecule which binds to a receptor.
Closed- but when an appropriate ligand binds to the channel structure, it changes shape slightly and causes it to open.
Neurotransmitters but can also be drugs.
This can excite a neuron and get depolarisation started.
Activation of receptors by neurotransmitters (NT):
Explain how it works.
What are receptors specific to?
Have a presynaptic neuron- this just fired- as a result- an action potential has reached the terminal buttons- causes neurotransmitter molecules to be released- diffuse across the synapse- bind to receptors on the postsynaptic membrane- these neurotransmitters are what we call ligands of these receptors.
To a particular neurotransmitters- e.g. there might be a dopamine receptor which dopamine binds too.
What do released neurotransmitters do?
What are receptors specific for?
Essentially, what happens?
What is this responsible for?
Produce signals in postsynaptic neurons by binding to receptors.
Receptors are specific for a given NT.
They diffuse across- bind to receptors- cause channels to open or close.
Most things that happen in your brain- it is being triggered by ligand gated sodium channels.
What is the process?
What happens if this is in the region of the axon hillock?
A NT goes across the synapse- bind to ligand gated sodium channel- cause positively charged sodium ions to rush into a cell- making it a bit depolarised- this spreads.
Makes it sufficiently depolarised- that it hits the threshold of excitation- you will have an action potential.
What exists?
What can NTs be?
NTs- which do the opposite- they can go across and bind to chloride channels- letting negatively charged chloride ions in- which makes the cell more polarised- so less likely to fire.
Some are excitatory and some are inhibitory.
Post-synaptic potentials (PSPs):
What leads to a postsynaptic potential?
What does NTs opening sodium channels and letting positively charged sodium ions cause?
Neurotransmitter (ligand) binding to a receptor leads to a postsynaptic potential i.e. a change in the postsynaptic membrane potential.
Depolarisation (making the membrane potential less negative) = excitatory postsynaptic potential (EPSP)- makes it more likely to fire.
What happens if channels, which let negatively charged chloride ions in, are open?
Unlike action potentials which are all or nothing, how are these?
Hyperpolarized (making the membrane potential more negative)- inhibitory postsynaptic potential (IPSP)- less likely to fire.
They vary in size- a lot of NT cause big excitatory neurotransmitter making it more likely to the neuron will fire- a little bit of neurotransmitter will cause little excitatory postsynaptic potential and not a big effect.
What does whether or not a neuron fires depend on? How would you know?
Add together all the excitatory potentials- then take away the inhibitory ones- when you balance that all out, does it reach the threshold or not?
EPSPs and IPSPs:
What are PSPs?
What happens when they travel passively from the site they origin in?
What else happens as they travel?
Graded potentials- their size varies.
Become weaker- as they get away from the point they started at.
Decremental- they get smaller as they travel.
Continuation from EPSPs and IPSPs:
What is not enough for a neuron to fire?
What is needed to get to -65mV to trigger an action potential?
What is spatial summation?
What is temporal summation?
What happens if either of these is enough?
Look at the pictures in the doc.
One EPSP alone- usually need a couple- can either be from different neurons or multiple potentials from the same neurons happening in a very short period of time.
Temporal and/or spatial summation.
Add together excitation from several neurons.
Add together multiple stimuli from the same neuron in a very short period of time.
Will trigger an action potential.
If one neurons stimulates another and the other does the same thing and you add them together, what will happen?
What happens if you add two inhibitory ones together?
What happens if you add two positive excitatory inputs and inhibitory input?
How would you know whether the threshold of excitation is reached (a neuron fires)?
Essentially, what happens?
Is three added together enough to hit the threshold and get an action potential?
You will get more stimulation.
Will get a big negative one.
You get nothing.
When you add these altogether.
Add them together- burst of excitatory action potentials- it hits the threshold- have an action potential.
Yes.
Give some information about excitatory.
What is releasing inhibitory neurotransmitters?
What do they kind of do?
What does it depend on?
What can certain drugs do?
Excitatory- inputs to neuron releasing neurotransmitters- open ion channels- let sodium through.
Other neurons connected to it- open chloride channels do the opposite.
Fight each other.
Axon hillock- it is the decision maker- it asks things like is there enough simulation? And should I fire or not?
Enhance the effects of inhibitory neurotransmitters- make it less likely the neurons will fire- having a sedatory effect.
