electrophysiology Flashcards
what is electrophysiology
measuring electrical activity in biological tissue
brain, heart, muscles, eyes, cochlea, nerves, SC
what do electrophysiological recodings measure
measure potential difference between inside and outside the cell
membrane potential
What is the ionic basis for the potential difference between the intracellular and extracellular space?
resting membrane potential
K+ selective ‘leak’ channel
K+ ions flow across the membrane from the inside to the outside
inside of the cell to become more negative and outside to become more positive.
chemical and electrical gradients
moving in opposite directions
reach equilibrium
What are the pros and cons of using dissociated neuronal cultures to study electrophysiology?
+ = cell easily accessible for intracellular recoding
- = no anatomical correlate - cells not in physiological environment - only study early developmental stages
What are the pros and cons of using acute brain slices to study electrophysiology?
+ = local circuits intact = can study developmental stage = anatomically relevant
- = long range inputs/outputs severed - not physiological environment
What are the pros and cons of using whole animals to study electrophysiology?
+ = all circuits intact - can correlate activity with behaviour
- = technically challenging – for intracellular recordings
how to record intracellular membrane potential
Starting using patch clamp recordings
ensure cell membran remains in tact
Allows current through single ion channels
Caputures by the pipette
Record activity of channel itself
difference between using sharp and patch pipette
sharp = high tip resistance , pokes a hole
patch = low tip resistance , perfuses cell with pipette solution
equilibrium potential
the membrane potential at which there is no net flow of ions
what is ionic equilibrium potential determined by
intracellular con
extracellular con
valance of the ion
what equation is used to measure the potential of an ion
Nernst equation
Ex = 61.5/z log(1) [X] out/ [X] in
how can we control equilibrium potentials
controlling intra and extracellular ion conc
what happens to the membrane potential is we open sodium channels (e.g apply channel agonist)
opening of sodium permeable channel = depolarisation of membrane potential
what happens to the membrane potential is we open potassium channels (e.g apply channel agonist)
opening potassium permeable channel = hyper polarisation of membrane potential
why in juvenile neurons is the conc of Cl more than resting membrane potential
Ecl > V(rest) = activated Cl- channels depolarise the membrane
K+/Cl- co transporter (KCC2) pump = pumps cl- ions out of the cell = contributes to E(Cl)
KCC2 not expressed early in development = so cl- conc inside is higher and Ecl is more depolarised
so activation cl- channels in early development = depolarisation
what is Ecl like in adult neruons
normally Ecl < Crest = activating cl- channels hyper polarises the nearons
KCC2 protein function
the K+/Cl- co transporter - pumps Cl- ions out of the cell.
EPSP
excitatory postsynaptic potential
record the activity of one single neueon
how do we use electrophysiology to study synapses
record activity of ion channels across membranes
ap - pre synaptic cell releases neurotransmitters - act on post synaptic receptor - ion channel - cause ion channel to open - stream of ions flow - record from post synaptic neuron
where on the neuron would u measure EPSP
At the soma
what is a field potential / fEPSP
as positive ions move into the cell
extracellular space becomes more negative
record the activity of the extracellular space when many synapses happens simultaneously
intracellular vs extracellular recordings
intracellular = EPSP = ion channel activities
Extracellular = fEPSP = stream of ions going inside the cell
what does current clamp measure
membrane potential
used to monitor the effects of manipulation (drugs) on membrane potential
voltage clamp measure
records the current
used to study the underlying biophysical properties of channels in the membrane and effects of manipulation (drugs) on these
ohms law
V = IR
how do electrophysiological amplifies stimulate cells
injecting current
intracellular recording of voltage are called Current clamp
what happens to membrane potential with current clamp
Vm = more positive as it moves towards E (Na)
what happens to membrane potential with a voltage clamp
it does not change
to counteract the flow of + sodium ions into cell
amplifies injects negative current
voltage clamp monitors the in and outs
EPSC
V clamp at -80mV
amplifier injects negative current to maintain the cell at -80mV to oppose the flow of + charge ions via glutamate receptor
