[SOUND]. Okay.
So, up until now I really spoke only about the case where everything was, so
to speak, passive. Passive resistor, passive capacitor, and
a battery, passive battery, the battery that these constant.
So, this was minus 70 millivolts. And this had some value depending on the
cell type and, and size. And this has the capacitance depending on
the capacitance of the cell. I didn't tell you much about the values
of R and of C but I want to tell you now, just to give you a ballpark, just to tell
you that this R multiplied by C. This time constant that I just mentioned,
R multiplied by C, R multiplied by C, which I call the membrane time constant,
is on the order in central neurons in our brain, on the order of 20 milliseconds or
so. Milli is a thousandth of, 10 to the power
of 3. So, this is 20 millisecond, much smaller
than a second. And that's about the correct time of a
typical RC multiplication, RC properties of a bunch of membrane in the brain.
About twenty milliseconds, it could go down to 10 milliseconds, maybe 5
milliseconds, depending on how leaky is the membrane of this particular cell.
But you may remember 20 milliseconds time constant.
Okay. So, this was the passive situation here.
[SOUND]. And now I want to go into the synaptic
potential. Because I told you before, nobody from
the outside inject currents into cells. So who, where, is the source of current
to cells? And these are the synapses.
So, let me draw symbolically a synapse onto this cell.
Let's draw it like this. This will symbolize an axon terminating
on the sol, on, on the cell. So, remember that we spoke early on, when
we spoke on the anatomy of cells. I hope you remember that there were,
typically there were dendrites with spines.
So, this was a piece of dendrite[SOUND] and there was an axon going here,[SOUND]
and there was this varicosity in the axon.