00:02
All right, there's five discussion questions here that we're going to cover.
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The first explain the differences among membrane potential, excitatory post -synaptic potential, epsp, inhibitory post -synaptic potential, ipsp, and action potential.
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The second is the conductance of which ion or ions cause an epsp or an ipsp.
00:30
The second or the third is explain the difference between temporar.
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And spatial summation.
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The fourth is what is the significance of summation of post -synaptic potentials in neural processing.
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And five, why does conductance of potassium ions have greater inhibitory effect than conductance of chloride ions? so the first one, let's look at the different types here.
00:59
So membrane potential generally is used to refer to the resting membrane potential or e sub m of any given cell.
01:07
Normally in an excitable cell, this is minus 70 millivolts.
01:11
This is due to the selective permeability of the membrane, the donning equilibrium, and the sodium potassium pumps, right? so the cell tends to be more negative on the inside than on the outside.
01:27
This is primarily driven by potassium permeability, as it's the most permeable of the ions not only because of leakage channels but the sodium potassium pumps are moving three sodium out to potassium in for every atp molecule an action potential is a transient change in membrane potential with a depolarization hyperpolarization and normalization and so that's what this red line depicts so here's the membrane potential if we get a excitatory stimulus that reaches are a threshold of about 15 millivolt.
02:06
Then we have sodium channels that open up, causing sodium to rush into the cell, causing a rapid increase in the charge, up to about positive 30 milovolts.
02:23
At this point, the sodium channels that were opened, allowing sodium to come in, those close.
02:32
And then we have potassium channels.
02:34
Which are delayed rectifying.
02:37
So the change in voltage now opens up all these potassium channels and potassium flows out of the cell, rapidly polarizing the cell.
02:53
In fact, hyperpolarizing, going to about minus 90 millivolts.
02:58
Okay.
03:00
And then those close, and we try to get back to normal with the sodium potassium pumps.
03:09
Again sodium out potassium in depolarizing this cell getting back to minus 70 millibolds okay if we talk about excitatory post -synaptic potentials and inhibitory post -synaptic potentials that's essentially the impact it has on the next cell the post -synaptic cell so excitatory would be depolarizing we're going to make the membrane more positive.
03:42
And that generally involves the influx of sodium.
03:49
Inhibitory makes the membrane more potential or more negative or hyper -polarizes.
03:56
So it makes it more negative.
03:57
So maybe we go down to negative 75, negative 80.
04:02
So we can do this by bringing in chloride ions or moving out potassium ions.
04:11
So again, again, inhibitory is to hyper -polarize, making it more negative...