Changing Membrane Potentials Flashcards
Define depolarisation.
A decrease in the size of the membrane potential from normal value.
Cell interior becomes less negative (-70 becomes -50mV)
Define hyperpolarisation.
An increase in the size of membrane potential form its normal value.
Cell interior becomes more negative (so -70 becomes -90mV)
How ar membrane potentials changed?
By changing a membranes selectivity between ions in its ionic permeability. So the ion concentration and therefore cell voltage changes
How does membrane permeability move closer to a specific ions equilibruim potential?
By the membrane becoming more permeable towards that ion
How does hyperpolarisation occur?
The opening of K+ channels (move out so cell more neg). Or the opening of Cl- channels (move in so cell becomes more negative)
How does depolarisation occur?
Opening Na+ channels (Na+ moves in so cells more positive) or opening Ca2+ channels (moves in so cell more positive)
Real cell membranes have imperfect selectivity (sleet for more than one ion) how does this effect membrane eotenital?
The potential is the average permeability of all ions.
Each ions contribution to the ,membrane potential depends on how permeable the membrane is to that ion.
Give an example of a receptor/channel that selects for more than on ion. What are these ions?
Nicotinic Acetylcholine receptors.
Has a gated pore that opened when Ach binds. They predominantly select for Na+ but that will also carry K+ or Ca2+ ions. So are selective for Cations.
Where does nicotine Acetylcholine receptor push the membrane potential towards?
Towards 0 as this is between E(Na) and E(K).
What are the different types of gating that can occur at channels?
Ligand gating
Voltage gating
Mechanical gating
What is ligand gating and give an example.
The channel opens/closes in response to binding of a chemical ligand
Eg) channels on synapse that respond to extracellular transmitter
Eg)channels that respond to intracellular messengers
What is voltage gating and give a example.
Channel opens/closes in response to changes in membrane potential.
Eg) channels involved in APs
What is mechanical gating and give an example.
Channel opens/closes in response to membrane deformation.
Eg)channel in mechanoreceptor such as carotid sinus stretch receptors and hair cells
What is FAST synaptic transmission?
This means the receptor protein is also an ion channel.
The transmitter binding causes the channel to open, so response is direct
What is an excitatory synapse? And what happens ther?
Excitatory transmitters open ligand-gated channels that cause membrane depolarisation.
Permeable to Na+, Ca2+, or cations in general
This causes an Excitatory post-synaptic potential.
What are some features of an excitatory post-synaptic potential?
Longer time cause than an AP
Graded response to amount of transmitter ( more Ach = higher potentials. There is constant release of Ach but not enough to cause APs every time)
Transmitters include= Acetylcholine (in nerves) and glutamate (in the brain, a Ca2+ channel)
What is an inhibitory synapse and what happens there/
Inhibitory transmitters open ligand-gated channels that cause hyperpolarisation.
They’re permeable to K+ or Cl-
Cause an inhibitory pot-synaptic potential
What do inhibitory post-synaptic potentials do and give some transmitter examples.
They make the membrane potential more negative, so its further form AP threshold.
This prevents constant AP firing so is important. If stopped, excitability increases and seizures may occur
Transmitters include=Glycine and y-aminobutyric acid (GABA)
What is SLOW synaptic transmission?
The receptor and channel are seperate proteins.
They may be direct G-protein gating or gating via an intracellular messenger.
What is direct G-Protein gating?
The receptor binds to the membrane and the G-Protein than activates the channel to conformationally change it.
It’s a localised method and is quite rapid.
What is gating via an intracellular messenger?
It’s throughout the cell and may be simplified by a cascade.
The receptor and G-protein activate Na enzyme beginning a signalling cascade. The signals diffuse through the cell to the channel activating it. Could use an intracellular messenger or the phosphorylator protein kinase.
What 2 other factors influence membrane potential?
Change in ion conc
Electrogenic pumps
How do changes in ion coin influence membrane potential?
Most important is the extracellular K+ conc.
It can make the cell more polarised meaning it has a more excitable nature, so AP’s are fired more easily.
When the conc changes suddenly it causes the rapid firing of AP”S (seizures etc), over time it begins to reduce excitability causing difficulty moving.
How do electrogenic pumps influence membrane potential?
Eg is NA/K-ATPase
One positive charged is moved out for each cycle. In some cells this contributes a few mV to the membrane potential (makes it more negative) but this is only a small direct effect.
The bigger effect is indirect, via active transport the pumps are responsible for the entire potential as they set up and maintain the ion gradients.
