Lecture 8 - Changing Membrane Potential Flashcards
How are changes in membrane potentials used in signalling?
Action potentials in nerves and muscle cells
Neuromuscular junctions
Hormone and neurotransmitter secretion
Postsynaptic actions of fast synaptic transmitters
What is depolarisation?
A cells membrane potential becoming more positive from its normal RMP
Cell interior is less negative
What is Hyperpolarisation?
When cell becomes more negative than its RMP
What is repolarisation?
A cell getting closer to its resting membrane potential
How can repolarisation be happening but the cell could be getting more positive or more negative?
If cell has just depolarised, the membrane potential gets more negative to get closer to RMP
If cell has just hyperpolarised, the membrane potential gets more positive to get closer to RMP
How does increasing membrane permeability to a particular ion affect the membrane potential?
Shifts the membrane potential towards the equilibrium potential for that ion
In an excitable cell describe what happens in terms of depolarisation, repolarisation and hyperpolarisation what happens when an action potential is fired starting with the Resting membrane potential stage RMP:
RMP
Depolarisation
Repolarisation
Hyperpolarisation
Repolarisation
Depolarisation
Repolarisation back to RMP
In an excitable cell, the cell membrane has an increased permeability to what ion in the FIRST DEPOLARISATION and which direction does this ion move?
Na+
Na+ INFLUX
Cell membrane potential made more positive (Towards ENa)
In an excitable cell, after the cell massively reduces its permeability to Na+ the cell membrane has an increased permeability to what ion in the FIRST REPOLARISATION and which direction does this ion move?
K+
K+ EFFLUX
Cell becomes more negative inside
What happens in the hyperpolarisation stage of an action potential?
Too much K+ EFFLUX
The K+ channels close slowly so too much moves out
How does the cell repolarise after the hyperpolarisation and how is later depolarisation caused?
(After the final depolarisation cell will repolarise back to RMP)
Na+/K+ ATPase helps re establish gradient
Overcompensation by Na+/K+ ATPase temporarily leads to further depolarisation
Opening of what ion channels will cause cell hyperpolarisation and why?
K+ channels
Too much K+ EFFLUX
Opening of Na+ or Ca2+ has what affect of a cell?
Depolarises (makes more positive inside)
What causes changes in membrane potential?
Changes to activity of ion channels (selective permeability)
How is the membrane potential of a cell determined when it is not perfectly selectively permeable to a single ion?
Depends on how permeable the membrane is to all the different ions determines their contribution of membrane potential
What equation takes into account different ions contributions to membrane potential?
GHK
What are the 3 ways by which channel activity (membrane permeability to an ion) so opening/closing can be controlled?
Ligand gating
Voltage gating
Mechanical gating
What is ligand gating in controlling membrane permeability to an ion?
A channel opens or closes in response to binding of a chemical ligand
What is voltage gating in controlling membrane permeability to an ion?
Channel opens or closes in response to changes in membrane potential
What is mechanical gating in controlling membrane permeability to an ion?
Channel opens or closes in response to membrane deformation (stretch receptors)
What is the short hand for Nicotinic acetylcholine receptor?
nAChRs
Or
nACh receptor
How many subunits does a Nicotinic Acetylcholine receptor (nAChRs) have?
5
What is the ligand that binds to an nAChRs?
Neurotransmitter - ACh (Acetylcholine)
How many alpha subunits are on a nAChRs?
If this is where ACh binds how many ACh need to bind for the conformational change to happen to open the channel?
2
2 ACh. 1 on each Alpha subunit
Nicotinic Acetylcholine receptors are not extremely selective, what 3 ions are able to pass through it once ACh has bound causing the conformational change?
Na+/Ca2+ allowed into cell
K+ allowed out of cell
Where are nACh receptors located?
On muscle membrane at neuromuscular junction
What happens to the muscle membrane potential once ACh has bound to the nACh receptors on its membrane?
It depolarises towards 0mV since this is an intermediate between the equilibrium potential for both Na+ and K+
What is reversal potential?
The potential of the membrane that is reached as the potential of the membrane is driven between an intermediate point of all the ions its permeable to
Here there’s no net flow of ions into or out of the cell
Between what cells do chemical synapse occur between?
Nerve - nerve
Nerve - muscle
Nerve - gland
Sensory - nerve
What occurs at a chemical synapse?
Chemical transmitter released from presynaptic membrane into cleft once action potential is received, the transmitter then binds to receptors on the postsynaptic membrane altering its permeability to ions
What are the 2 types of synaptic transmission?
Fast
Or
Slow
What is fast synaptic transmission?
When the receptor protein is also the ion channel
Transmitter binding directly causes the channel to open
What is slow synaptic transmission?
When the receptor and ion channel are separate proteins
Which type of receptor is normally involved in slow synaptic transmission?
G-Protein coupled receptors (GPCRs)
What are the 2 ways which a G-Protein coupled receptor can carry out slow synaptic transmission?
Ligand binds to GPCR activating G protein which binds to the ion channel causing a conformational change
Ligand binds to GPCR activating G protein which activates and enzyme causing a signalling cascade producing a messenger which will bind to the ion channel
What are the 2 ways which a G-Protein coupled receptor can carry out slow synaptic transmission?
Ligand binds to GPCR activating G protein which binds to the ion channel causing a conformational change
Ligand binds to GPCR activating G protein which activates and enzyme causing a signalling cascade producing a messenger which will bind to the ion channel
Which slow synaptic transmission is faster, direct G protein gating or gating via intracellular messenger?
Direct G protein gating
What is an excitatory synapse?
When an excitatory transmitter opens a ligand gated ion channel that causes membrane DEPOLARISATION
What is an Excitatory post-synaptic potential?
The depolarisation resulting form an excitatory transmitter opening a ligand gated ion channel like nAChRs allowing influx of Na+ and Ca2+
(Longer than an action potential)
more transmitter = longer it stays depolarised
What is an inhibitory synapse?
When an inhibitory transmitter opens ligand gated channels that cause hyperpolarisation
E.g opens channels allowing K+ out and Cl- in
What is an example of an inhibitory synapse?
GABA-A receptor
How does a GABA-A receptor act as an inhibitory synapse?
Ligand binds to channel
Makes channel permeable to Cl- so Cl- moves into postsynaptic membrane making it more negative (hyperpolarisation)
What is a key characteristic of discrete fast Excitatory Post synaptic potential and Inhibitory Post synaptic potential?
Rapid onset
Gradual decay
What does the size and length of the Excitatory post synaptic potential depend on?
Intensity or magnitude of stimulus
How long does the fast depolarising current of an Excitatory Post synaptic potential last that has occured as a result of a short stimulus?
10ms
