ELECTRO 1 Flashcards
Describe the various techniques for electrophysiological recording
-local EEG
-extracellular LFP
-intracellular recording
Extracellular LFP
current flows → local field potential
Describe the local EEG
Crudest/lowest resolution
cortical thickness packed with neurones - mostly pyramidal cells
regular orientation and layers and apical dendrites that go vertically in parallel
Intracellular recording
finer/highest resolution
as you increase stimulation = increased frequency of AP = rate coding
AP frequency increases with stimulus intensity
Membrane potential change → changes direction and amplitude of stimulus
Distinguish between intracellular vs extracellular
EC: occurrence of AP
cannot record voltage difference across membrane (membrane potential, Vm)
spikes in nearby neurons cause local extracellular current flow which can be detected as small transient voltage change
IC: membrane potential and individual synaptic
records voltage difference across cell membrane (Vm)
State the electrical properties of the neuron
Voltage: Battery -70mV Na/K equilibrium = ion pump
Capacitance: capacity to store in separate change ⇒ delayed response
-determines rate of responses of membrane = membrane time constant
-lipid bilayer membrane impermeable to ions - resistant BUT pores allow ion flow
Increase in ion channels opening = decreases resistance
Faster time constant- the more quickly it will approach final value = shorter time constant = longer it would take
Explain the difference between action potentials and graded potentials
Graded potentials: subthreshold changes in Vm due to intracellular current injection in an electrophysiological experiment.
AP/SPIKES SYNAPTIC/GRADED
Large (~100mV) small (<1 mV)
Faster (c. 1ms) slower (c. 10ms)
All-or-nothing graded
cannot summate can summate
active passive
What are neuronal inputs and outputs?
Neuronal outputs: APs (spikes) propagated down the axon
APs potentials are actively propagated
Neuronal inputs: EPSPs and IPSPs generated in dendrites and soma in response to spikes in presynaptic neurons
synaptic potentials are graded potentials
they are passively propagated from dendrites to soma
An AP in a presynaptic neuron triggers a PSP in a postsynaptic neuron. Explain further.
Neurotransmitter secreted from presynaptic binds to receptor on postsynaptic membrane - opening ion channels and allowing local current flow
results in local change in Vm which may de- or hyperpolarising
changes in Vm due to single PSPs are usually small: in the mV range
PSPs are graded potentials they can summate
SUMMATION = longer time constant
Describe Synaptic integration
over any given (brief) time window spatial and temporal summation determine the value of Vm
If positive to threshold, AP generated, otherwise not
EPSPs: +ve
IPSPs: -ve
Describe Spatial summation
different presynaptic neurons with synapses on different spatial locations on the postsynaptic neuron can be active simultaneously - individual PSPs can summate
Describe Temporal summation
time course of AP is slower than PSP. If twi presynaptic APs are fired in rapid succession, PSP due to 2nd AP can sum with that due to 1st.
Synaptic potentials slower to rise and decay due to passive electrical properties of membrane (time constant (C))
if intraspike interval short enough ⇒ frequency high enough then 2nd AP before PSP
Explain the effect of membrane space on synaptic integration
increases with square root of diameter
increases with membrane resistance
decay of voltage along membrane
Explain the effect of time constants on synaptic integration
T = RC
Explain membrane leakage
Vm +10 from presynaptic neuron ⇒ leaking occurs ⇒ less than -10 to soma and postsynaptic neuron = space constant
The input signal to a neuron consists in in graded changes in Vm due to summation of excitatory and inhibitory postsynaptic potentials over a given time window.
Time constant, tau, is given by membrane resistance multiplied by capacitance (t=RC). By opening more ion channels we can create faster responding neuron
