Electrophysiology Flashcards
How is resting potential established?
3Sodium/2Potassium ATPase pumps in the membrane bring potassium in
Potassium flows out down concentration gradient through leaky channels
Anions cannot follow, electrical gradient forms
Electrochemical equilibrium
3 Models that can be used to study electrophysiology
Whole animal models
Acute brain slices
Dissociated neuronal cell cultures
What are dissociated neuronal cell cultures?
Neuronal stem cells, typically from a rat, are grown in vitro into an artificial synaptic network
Pros/Cons of dissociated neuronal cell cultures
Easy to record from
Difficult/impossible to replicate exact in vivo conditions
Haven’t been developed in a normal physiological environment
What are acute brain slices?
Slice of brain 300-400 microns thick
Pros/Cons of acute brain slices
Can be taken at any developmental stage
Difficult/impossible to replicate exact in vivo conditions
Pros/Cons of whole animal models
Expensive
Tight regulations on living conditions
Technically very difficult to record from
Can provide in vivo results - most accurate
All circuits of brain fully intact
Two types of equipment for recording electrical activity?
Patch pipette - wide tip, sucks up cell membrane, cytoplasm be comes continuous with inside of pipette
Sharp electrode - pokes hole in cell, filled with liquid that matches the cell potential
What is Ohms law (and units)?
Voltage (V) = Current (Amps) X Resistance (Ohms)
What is a current clamp recording?
Current is injected into the cell Injection of negative current leads to hyperpolarisation Change in voltage is proportional Record the voltage Used to calculate resistance
What affects resistance?
Resistance is affected by the ion channels in the membrane, and whether they are open or closed
When applying a drug that opens ion channels, resistance will decrease
What is an EPSP?
EPSP = Excitatory Post Synaptic Potential
It is the (positive) membrane potential change caused by cation influx/depolarisation
Measured using a current clamp recording
What is a single unit recording?
Using a single electrode to record the fieldEPSP from the extracellular space of a group of neurons
Records the overall result of many different neurons at once
Pros/cons of a single unit recording
Can be recorded in vivo
Records an ‘average response’ from many neurons, so these is less variation
No disruption of cell contents
Cannot identify which neurons are influencing the fEPSP
Neurons that are closer to the electrode will have stronger influence
What are multi-electrode recordings?
Record the fEPSP using multiple electrodes positioned at different points
Eliminates the effect of neurons closer to the electrode having more effect
What is functional imaging?
A way of recording/measuring neuronal activity by measuring the calcium influx
How does functional imaging work?
The gCaMP protein is applied to cells
When 4 calcium ions bind to the gCaMP protein, it undergoes a conformational change which causes it to become fluorescent
3 methods of measuring neuronal activity
Single Unit recording
Multi electrode recording
Functional imaging
What type of graph is used to analyse an action potential?
Phase plane plot
What are the x and y axes of a phase plane plot?
x = voltage (mV) y = 1st derivative of the AP
What 4 things can a phase plane plot tell you (and at which point on the graph are they)?
Draw this out
Top point = Maximum rate of rise
Furthest right = AP peak
Lowest point = Maximum rate of fall
Magnitude of the after hyperpolarisation = distance between the lines on the left
What is v1/2 activation and what does it tell you?
Half maximal activation voltage
Lower v1/2 activation indicates that channels become activated at a more hyperpolarised (lower) action potential threshold - more excitable
3 sodium channels present in the hippocampus, which neuron type are they present on and what is the v1/2 activation?
Nav1.1, Interneurons, -20mV
NaV1.2, Pyramidal, -24mV
NaV1.6, Pyramidal, -29mV
What is the structure of a sodium channel?
Large alpha subunit
Properties are modulated by forming covalent bonds with B1 and B2 subunits
Modulated by phosphorylation
‘Ball and chain’ plug
