Fast excitatory and inhibitory synapses and how they integrate their signals (Dr. Edwards) Flashcards
What are we talking about when we say “inward” and “outward” current ?
We are following the movement of POSITIVE ions.
Depolarasation is caused by an inward current and hyper polarization by an outward current.
At a positive voltage, will there be an inward or outward current through the AMPA receptor ?
What about the GABA receptor ?
An outward current for the AMPAR.
A much stronger outward current for the GABA receptor.
At a positive negative, will there be an inward or outward current through the AMPA receptor ?
What about the GABA receptor ?
A inward current for the AMPA receptor, which gets stronger as the voltage gets more negative.
An outward current for the GABA receptor until about -80mV, then an inward current.
At voltage zero, will there be an inward or outward current through the AMPA receptor ?
What about the GABA receptor ?
There will be no curent flow through the AMPAR.
There will be a rather strong outwards current through the GABA receptor.
What current flow (aprox) will be detected if 10s (tens) of channels open ?
10s of pA
What is the amplitude of the current (at a particular voltage e.g. -70mV) determined by ?
The nb of postsynaptic receptor available, the probability of neurotransmitter release and the nb of sites.
What is Ohm’s law ?
V = IR
How does inhibition work ?
It sends the voltage in the other direction and makes the membrane more leaky (because more channels are open), which lowers its resistance.
What is membrane capacitance ?
What is the membrane capacitance of the lipid bilayer ?
Capacitance arises from the fact that the lipid bilayer is so thin that an accumulation of charged particles on one side gives rise to an electrical force that pulls oppositely charged particles toward the other side. The capacitance of the membrane is relatively unaffected by the molecules that are embedded in it, so it has a more or less invariant value estimated at about 2 µF/cm2.
What is the membrane time constant ?
The “membrane time constant” of a neuron is simply a way of measuring how quickly a neuron’s voltage level rises and decays to its “resting state” after it receives an input signal.
Therefore, the time constant represents the speed with which a neuron can respond to change, typically the time taken to reach (1-(1/e))Vmax for the rising phase, or to reach (1/e)Vmax for the falling phase. The mathematical constant “e” is around 2.7, and 1/e = 0.368.
How can we calculate the time constant ?
T = RC
where R is the resistance across the membrane and C is the capacitance of the membrane.
What is the implication of the time constant for neurons ?
The implication is that since there is a time before the membrane reaches 67% of Vmax, so Vmax can only be reached if the current flows for long enough compared to the time constant T.
