Distribution of ions in the cell?
Sodium, calcium and chloride are higher outside the cell.
Potassium is higher inside
What ion gives rise to the resting potential of the cell?
What is the resting potential of the cell?
What pH are cells normally at?
What ion is actively pumped out by active transport?
How to calculate pH?
Depends on the H+ ions.
What is the pH inside the cell?
Very similar to the outside
How 2 types of energy barrier does the membrane present to stop ion crossing?
- Schematic of a postive charged cation solvated by polar water moelcules.
- Lipid bilayer.
Means it takes a lot of energy to actively bring something into the cell
The primary route for ions to cross the membrane.
Others are activated by specific stimuli eg. voltage.
What ion channels are open at rest?
Different to patch clamp
High electro-resistance (not too high about 3mmol)
Records the intracellular voltage
Name the 3 types of electrophysiological recordings?
- Extracellular recording
- Intracellular recording
- Whole-cell patch recording
What are the 3 factors responsible for the uneven distribution of ions?
- Selective permeability of the membrane.
- Large organic anions within the cytoplasm.
- Ion pumps
For steady state?
Must be no net movement of ions into or out of the cell.
Electrically neutral between intra and extracellular
What is the ion concentration outside and inside the cell
Since potassium channels are open at rest.
Why doesnt potassium passively diffuse?
Well if potassium left the cell.
The cell would become negative
Negative charge attracts cation (like potassium)
Therefore brings back potassium ions back into the cell
The voltage in which there is no net movement of ions
The work required to keep the equilibrium?
As potassium is diffused outwards through the membrane
Increase in negative charge
Work is required to overcome this pull and prevent flow of potassium
The work to keep the equilbrium equation?
Work equation required to oppose the electrical froce tending to pull potassium back into the cell?
What is the gas constant value?
What is the faraday's constant?
The work done to overcome the electrical difference for potassium must equal?
The work done to overcome the chemical difference
Used to determine the potential difference
What does the graph for extracellular potassium vs membrane potential?
Should be linear
Something else is taking effect
More depolarised than the potassium equilibrium potential (-85mV)
Caused by a slight permeability to sodium.
Inward leak causes the more depolarised value.
What is the dynamic range of voltage the cells can work between?
34 -> -85mV
34mV: The potential difference for sodium
-85mV: the potential difference for potassium
What needs to be present for this inward leak of sodium ions?
A pump reguired to prevent depletion of intracellular potassium and build up of sodium
Sodium and potassium are transported
2K in: 3 Na out.
The action potential:
The different parts to it
AP goes beyound 0mV: overshoos.
what is the overshoot phase?
When the cell depolarises beyond the 0mV mark
What is the undershoot phase?
When the cell becomes so hyperpolarised it goes beyond the -70mV.
Goes to -85mV become returning back to -70mv
Action potential initiation?
positive feedbakc cycle occurs
Involving sodium channels.
Gives rise to all sodium channels becoming opened.
all or non event: either all the sodium channels opened or none.
Enough sodium channels are open
All or nothing response
Positive feedback no longer needed
What signals cause depolarisation?
Name the 2 gates of sodium?
M gate (activation gate)
H gate (inactivate gate- in the inside of the cell)
What is the name of that gate for potassium
Gating at work to cause AP?
The undershoot phase?
Vm goes below the resting membrane potential.
Sodium channels are inactivated
Potassium channels are still open
Known as the afterhyperpolarisation
The Refractory Period can be split into 2 periods?
Absolute refractory period:
- Sodium channels are still inactivated
- Never produce an AP.
Relative refractory period:
- Some sodium channels can open
- Can produce an AP with a stronger depolarisation.
Absolute refractory period and AP?
Is the interval during which a second AP can never be initiated- no matter how large the stimulus.
Relative Refractory period?
Interval immediately following absolute (AS37)
An initiation of a second AP is inhibited but not impossible
Voltage gated sodium channels?
Made up of?
6TMs make up a subunit
4 subunits make up the channel.
S4 domain is positivity charged.
How is the voltage gated sodium channel opened?
S4 domain is positively charged.
Attracted towards the inside of the cell when it is negatively charged- keeping it closed.
When the cell becomes depolarised the S4 moves up and opening the channel.
What happens when the voltage gated sodium channels are opened?
Sodium enters the cells.
Cause it to depolarise
Mechanism for sodium channel inactivation
4 subunit domains
Intracellular loop between 3 and 4 that is attracted into the inner mouth of the channel at depolarised potentials.
Ball and chain model of inactivation
Adds a wire into the inside of the cell and inject crent
Ability to control the membrane potential
Name the 3 patch clamp recordings:
How do you get to each one?
Inhibits the firing of AP in nerves by binding to voltage-gated sodium channels.
Block voltage-dependent potassium channels.
Prolongs the AP.
Distribution of ion channels in neurones
eg. neuromuscular junction
Sodium channels are clustered within the nodes of Ranvier.
Potassium channels are distributed between the nodes.
Name the 4 types of calcium channels?
Distrubtion of the different types of calcium channels?
L-type calcium channels?
Responsible for skeletal, smooth and cardiac tissue.
T-type calcium channels?
Transcient (Short) activation
Distrubed in the nodes of ranvier
N type or P/Q type calcium channel?
Alpha1 subunit forms the pore
Important for the uptake of calcium in the presynaptic cleft.
Glutamate (ions: sodium and calcium)
Important excitatory in brain
Ions: chlorine and HCO3-
Important in brain
How is glutamate and GABA synthesised?
Totography of the GABAA receptors?
Members of the cysteine-loop receptor family.
4TM domains. 5 subunits make the receptor
TM2: contributes to ion selectivity.
Totography of the glutamate receptor?
4 subunits per channel
Poor loop structure that participates in ion selectivity.
Excitatory postsynpatic potential
Stimulate production of AP if threshold is meet.
Inhibitory postsynpatic potential
Balance between EPSP and IPSP?
Balance between them
More EPSP needed to cause AP.
Name the 5 domains that make up the GABAA receptor?