Electrophysiology 2/3: The basis of bioelectricity Flashcards
what are the 2 types of transmembrane transporters? and what are their individual functions?
1) Pumps (Transporters) = maintains concentration gradients over a long a long term- via active transport as it uses energy
2) Channels - allow for the selective movement of ions across the membrane (‘downhill- no energy consumption)
- Direction of ion flow depends on both the concentration and electrical gradient
- Ion flow results in an electrical current
what is the difference in outcomes produced by transporters/pumps and channels in the neuron membrane?
Pumps/transporters maintain the concentration gradient using energy via active transport. Whilst, channels generate an action potential/ electrical current
What is the electrical model of the membrane?
Ion channels= Resistors
Lipid bilayer = capacitor
Describe the typical ion distribution across the membrane,
The resting membrane potential inside a neuron is generally negative compared to the outside, with a resting membrane potential of -70mv.
Define capacitance
Fixed property of the lipid bilayer as a result of the difference in extracellular and intracellular potentials- enables conductance within lipid
Principle to learn: Differences in voltage due to membrane capacitor
It isn’t the mass movement of charges that generate the changes of the membrane potential - just small shifts in the charging across the membrane that changes the membrane capacitor and results in different voltages.
what is the equilibrium potential?
The membrane potential at which there is no net movement of a specific ion across the membrane because the electrical force (due to voltage)and the chemical force (due to conc gradient) are balanced.
Does each ion have its own equilibrium potential?
Yes
what equation would you use to calculate the equilibrium potential?
Nernst equation
Write down the Nernst equation
check notes for this
what is Ek with normal physiological concentrations?
What is ENa with normal physiological concentration?
What happens if Vm is different from Eion?
What is the electrochemical driving force?
The force that determines the movement of ions across a membrane- the difference between the membrane potential and the ions equilibrium potential
the electrochemical gradient combines what two gradients?
The electrical gradient (charge difference) and the chemical gradient (conc gradient) to dictate the direction and rate at which ions flow.
The driving force is the difference between?
Vm and Eion
what is another name for equilibrium potential?
Reversal potential
The main point to remember
An ionic current ‘tries’ to change Vm so that it is closer to the equilibrium (reversal) potential for that ion.
This means that if there is an increase in conductance to a given ion, then the change in Vm will be towards the equilibrium potential for that ion.
when is Ohm’s law used?
To directly calculate the ionic current passing through a membrane when the electrochemical driving force is known
what is the equation used (Ohm’s law) to calculate the ionic current passing through the membrane when the electrochemical driving force is known?
Iion = gion (Vm-Eion)
I ion= ionic current for the specific ion
g ion = conductance of the membrane for that ion
Vm= membrane potential
Eion= Equilibrium potential of the ion
Describe difference in outward and inward current in terms of charge
Outward current = charge leaving the cell
Inward current= Charge entering the cell
Equivalent circuit model can solve for Vm at steady state. what is the equation?
Vm= (ENa x gNa) + (Ek x gK) /gNa + gK
Explain ISP in terms of reversal potential, membrane potential and hyper polarisation.
If the reversal potential (equilibrium potential) of the ion is more negative than the resting membrane potential, the ion flow will cause hyperpolarisation (making the inside of the cell more negative). This hyper polarisation moves the membrane potential further from the threshold, making the neuron less likely to fire= inhibition
Explain ionic equilibrium potential and synaptic reversal potential (EPSP)
If the equilibrium potential of the ion is more positive than the resting membrane potential (e.g. around -65mv), the ion flow will tend to depolarise the cell, making it more positive. Depolarisation brings the neuron closer to the threshold for firing of the AP= excitatory
