[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:00.33,Default,,0000,0000,0000,,
Dialogue: 0,0:00:00.33,0:00:03.15,Default,,0000,0000,0000,,In the last video, we talked\Nabout how the cell uses a
Dialogue: 0,0:00:03.15,0:00:08.28,Default,,0000,0000,0000,,sodium potassium pump and ATP\Nto maintain its potential
Dialogue: 0,0:00:08.28,0:00:11.11,Default,,0000,0000,0000,,difference between the inside\Nof the cell or the inside of
Dialogue: 0,0:00:11.11,0:00:13.68,Default,,0000,0000,0000,,the neuron and the outside-- and\Nin general, the outside is
Dialogue: 0,0:00:13.68,0:00:15.33,Default,,0000,0000,0000,,more positive than the inside.
Dialogue: 0,0:00:15.33,0:00:19.29,Default,,0000,0000,0000,,You have a -70 millivolt\Npotential difference from the
Dialogue: 0,0:00:19.29,0:00:21.00,Default,,0000,0000,0000,,inside to the outside.
Dialogue: 0,0:00:21.00,0:00:25.34,Default,,0000,0000,0000,,It's minus because the outside\Nis more positive.
Dialogue: 0,0:00:25.34,0:00:27.48,Default,,0000,0000,0000,,Less positive minus more\Npositive, you're going to get
Dialogue: 0,0:00:27.48,0:00:29.73,Default,,0000,0000,0000,,a negative number\Nand it's by -70.
Dialogue: 0,0:00:29.73,0:00:32.88,Default,,0000,0000,0000,,Now, I said that this was the\Nfoundation for understanding
Dialogue: 0,0:00:32.88,0:00:35.69,Default,,0000,0000,0000,,how neurons actually\Ntransmit signals.
Dialogue: 0,0:00:35.69,0:00:38.73,Default,,0000,0000,0000,,And to understand that, I'll\Nkind of lay a foundation over
Dialogue: 0,0:00:38.73,0:00:39.49,Default,,0000,0000,0000,,that foundation.
Dialogue: 0,0:00:39.49,0:00:42.71,Default,,0000,0000,0000,,I think then just the actual\Nneuron transmission will make
Dialogue: 0,0:00:42.71,0:00:43.76,Default,,0000,0000,0000,,a lot of sense.
Dialogue: 0,0:00:43.76,0:00:45.91,Default,,0000,0000,0000,,Even better, it'll make a lot\Nof sense why they even have
Dialogue: 0,0:00:45.91,0:00:49.07,Default,,0000,0000,0000,,these myelin sheaths and these\Nnodes of Ranvier and why we
Dialogue: 0,0:00:49.07,0:00:50.12,Default,,0000,0000,0000,,have all of these dendrites.
Dialogue: 0,0:00:50.12,0:00:52.39,Default,,0000,0000,0000,,Hopefully it'll all\Nfit together.
Dialogue: 0,0:00:52.39,0:00:55.25,Default,,0000,0000,0000,,So there are two types of\Nways that kind of a
Dialogue: 0,0:00:55.25,0:00:57.16,Default,,0000,0000,0000,,potential can travel.
Dialogue: 0,0:00:57.16,0:00:59.29,Default,,0000,0000,0000,,So there's two types\Nof signal transfer.
Dialogue: 0,0:00:59.29,0:01:02.29,Default,,0000,0000,0000,,I'll just call it\Nsignal transfer.
Dialogue: 0,0:01:02.29,0:01:04.26,Default,,0000,0000,0000,,I don't know what the\Nbest word for it is.
Dialogue: 0,0:01:04.26,0:01:06.71,Default,,0000,0000,0000,,The first one I'll talk\Nis electrotonic.
Dialogue: 0,0:01:06.71,0:01:08.19,Default,,0000,0000,0000,,It sounds very fancy,\Nbut you'll see it's
Dialogue: 0,0:01:08.19,0:01:09.44,Default,,0000,0000,0000,,a very simple idea.
Dialogue: 0,0:01:09.44,0:01:21.02,Default,,0000,0000,0000,,
Dialogue: 0,0:01:21.02,0:01:22.67,Default,,0000,0000,0000,,And the other one I'm\Ngoing to go over
Dialogue: 0,0:01:22.67,0:01:25.35,Default,,0000,0000,0000,,is an action potential.
Dialogue: 0,0:01:25.35,0:01:27.77,Default,,0000,0000,0000,,And they both have their own\Npositives and negatives in
Dialogue: 0,0:01:27.77,0:01:32.76,Default,,0000,0000,0000,,terms of being able to\Ntransmit a signal.
Dialogue: 0,0:01:32.76,0:01:36.36,Default,,0000,0000,0000,,We're talking about within the\Ncontext of in a cell or across
Dialogue: 0,0:01:36.36,0:01:38.27,Default,,0000,0000,0000,,a cell membrane.
Dialogue: 0,0:01:38.27,0:01:39.94,Default,,0000,0000,0000,,Let's understand what\Nthese mean.
Dialogue: 0,0:01:39.94,0:01:41.78,Default,,0000,0000,0000,,So let me get my membrane\Nof a cell.
Dialogue: 0,0:01:41.78,0:01:46.31,Default,,0000,0000,0000,,Let's say it's a nerve cell or\Na neuron, just to make it all
Dialogue: 0,0:01:46.31,0:01:49.13,Default,,0000,0000,0000,,fit together in this context.
Dialogue: 0,0:01:49.13,0:01:51.05,Default,,0000,0000,0000,,And we know it's more\Npositive on the
Dialogue: 0,0:01:51.05,0:01:52.30,Default,,0000,0000,0000,,outside than the inside.
Dialogue: 0,0:01:52.30,0:01:55.52,Default,,0000,0000,0000,,We know that there's a lot of\Nsodium on the outside or a lot
Dialogue: 0,0:01:55.52,0:01:58.28,Default,,0000,0000,0000,,more sodium on the outside\Nthan on the inside.
Dialogue: 0,0:01:58.28,0:01:59.32,Default,,0000,0000,0000,,There might be a little bit.
Dialogue: 0,0:01:59.32,0:02:05.66,Default,,0000,0000,0000,,And we know there's a lot more\Npotassium on the inside than
Dialogue: 0,0:02:05.66,0:02:08.18,Default,,0000,0000,0000,,the outside, but we know\Ngenerally that the outside is
Dialogue: 0,0:02:08.18,0:02:11.07,Default,,0000,0000,0000,,more positive then the inside\Nbecause our sodium potassium
Dialogue: 0,0:02:11.07,0:02:13.63,Default,,0000,0000,0000,,pump will pump out three\Nsodiums for every two
Dialogue: 0,0:02:13.63,0:02:15.43,Default,,0000,0000,0000,,potassiums it takes in.
Dialogue: 0,0:02:15.43,0:02:18.06,Default,,0000,0000,0000,,Now in the last video, I told\Nyou that there are these
Dialogue: 0,0:02:18.06,0:02:21.48,Default,,0000,0000,0000,,things called-- well, we could\Ncall them a sodium gate.
Dialogue: 0,0:02:21.48,0:02:23.81,Default,,0000,0000,0000,,A sodium ion gate, right?
Dialogue: 0,0:02:23.81,0:02:24.43,Default,,0000,0000,0000,,These are all ions.
Dialogue: 0,0:02:24.43,0:02:25.99,Default,,0000,0000,0000,,They're charged.
Dialogue: 0,0:02:25.99,0:02:28.42,Default,,0000,0000,0000,,Now let's say that there's some\Nreason, some stimulus--
Dialogue: 0,0:02:28.42,0:02:29.67,Default,,0000,0000,0000,,let me label this.
Dialogue: 0,0:02:29.67,0:02:35.43,Default,,0000,0000,0000,,
Dialogue: 0,0:02:35.43,0:02:39.99,Default,,0000,0000,0000,,That right there is my\Nsodium ion gate.
Dialogue: 0,0:02:39.99,0:02:41.66,Default,,0000,0000,0000,,And it's in its closed position,\Nbut let's say
Dialogue: 0,0:02:41.66,0:02:43.48,Default,,0000,0000,0000,,something causes it to open.
Dialogue: 0,0:02:43.48,0:02:45.70,Default,,0000,0000,0000,,We'll talk maybe in this video\Nor maybe this video and the
Dialogue: 0,0:02:45.70,0:02:47.33,Default,,0000,0000,0000,,next about the different\Nthings that
Dialogue: 0,0:02:47.33,0:02:48.20,Default,,0000,0000,0000,,could cause it to open.
Dialogue: 0,0:02:48.20,0:02:51.10,Default,,0000,0000,0000,,Maybe it's some type of stimulus\Ncauses this to open.
Dialogue: 0,0:02:51.10,0:02:52.91,Default,,0000,0000,0000,,Actually, there's a whole bunch\Nof different stimuluses
Dialogue: 0,0:02:52.91,0:02:55.48,Default,,0000,0000,0000,,that would cause it to open.
Dialogue: 0,0:02:55.48,0:02:56.37,Default,,0000,0000,0000,,But let's say it opens.
Dialogue: 0,0:02:56.37,0:03:00.56,Default,,0000,0000,0000,,What's going to happen\Nif it opens?
Dialogue: 0,0:03:00.56,0:03:02.56,Default,,0000,0000,0000,,So let's say we open it.
Dialogue: 0,0:03:02.56,0:03:04.79,Default,,0000,0000,0000,,Some stimulus opens-- what's\Ngoing to happen?
Dialogue: 0,0:03:04.79,0:03:06.88,Default,,0000,0000,0000,,We have more positive on the\Noutside than the inside, so
Dialogue: 0,0:03:06.88,0:03:08.46,Default,,0000,0000,0000,,positive things want\Nto move in.
Dialogue: 0,0:03:08.46,0:03:12.40,Default,,0000,0000,0000,,And this is a sodium gate so\Nonly sodium can go through it.
Dialogue: 0,0:03:12.40,0:03:14.96,Default,,0000,0000,0000,,So it's kind of a convoluted\Nprotein structure that only
Dialogue: 0,0:03:14.96,0:03:17.00,Default,,0000,0000,0000,,sodium can make its\Nway through.
Dialogue: 0,0:03:17.00,0:03:19.84,Default,,0000,0000,0000,,And on top of that, we have a\Nlot more sodium on the outside
Dialogue: 0,0:03:19.84,0:03:20.51,Default,,0000,0000,0000,,than on the inside.
Dialogue: 0,0:03:20.51,0:03:22.58,Default,,0000,0000,0000,,So the diffusion gradient's\Ngoing to want to make sodium
Dialogue: 0,0:03:22.58,0:03:23.32,Default,,0000,0000,0000,,go through it.
Dialogue: 0,0:03:23.32,0:03:26.65,Default,,0000,0000,0000,,And the fact that sodium's a\Npositive ion, the outside is
Dialogue: 0,0:03:26.65,0:03:28.27,Default,,0000,0000,0000,,more positive, they're going to\Nwant to run away from that
Dialogue: 0,0:03:28.27,0:03:30.34,Default,,0000,0000,0000,,positive environment.
Dialogue: 0,0:03:30.34,0:03:32.81,Default,,0000,0000,0000,,So if you open this, you're just\Ngoing to have a lot of
Dialogue: 0,0:03:32.81,0:03:35.04,Default,,0000,0000,0000,,sodium ions start to\Nflood through.
Dialogue: 0,0:03:35.04,0:03:40.25,Default,,0000,0000,0000,,
Dialogue: 0,0:03:40.25,0:03:43.19,Default,,0000,0000,0000,,Now as that happens, what's\Ngoing to happen if we go
Dialogue: 0,0:03:43.19,0:03:44.50,Default,,0000,0000,0000,,further down the membrane?
Dialogue: 0,0:03:44.50,0:03:47.11,Default,,0000,0000,0000,,Let's zoom out.
Dialogue: 0,0:03:47.11,0:03:50.65,Default,,0000,0000,0000,,So let's say that this is\Nmy membrane right there.
Dialogue: 0,0:03:50.65,0:03:54.16,Default,,0000,0000,0000,,Let's say that this is my open\Ngate right here and that it's
Dialogue: 0,0:03:54.16,0:03:56.99,Default,,0000,0000,0000,,open for some reason and a bunch\Nof sodium is flowing in.
Dialogue: 0,0:03:56.99,0:04:01.05,Default,,0000,0000,0000,,So all of this is becoming\Nmuch more positive.
Dialogue: 0,0:04:01.05,0:04:04.98,Default,,0000,0000,0000,,Let's say we had a voltmeter\Nright here.
Dialogue: 0,0:04:04.98,0:04:07.23,Default,,0000,0000,0000,,We're measuring the potential\Ndifference between the inside
Dialogue: 0,0:04:07.23,0:04:10.42,Default,,0000,0000,0000,,of the membrane a\Nand the outside.
Dialogue: 0,0:04:10.42,0:04:13.58,Default,,0000,0000,0000,,Let me do a little chart.
Dialogue: 0,0:04:13.58,0:04:17.19,Default,,0000,0000,0000,,I'm going to do the chart\Nhere on my voltmeter.
Dialogue: 0,0:04:17.19,0:04:20.58,Default,,0000,0000,0000,,And this is going to be the\Npotential difference-- or
Dialogue: 0,0:04:20.58,0:04:26.75,Default,,0000,0000,0000,,we'll call it the membrane\Nvoltage or the voltage
Dialogue: 0,0:04:26.75,0:04:28.00,Default,,0000,0000,0000,,difference across the\Nmembrane-- and
Dialogue: 0,0:04:28.00,0:04:31.15,Default,,0000,0000,0000,,let's say this is time.
Dialogue: 0,0:04:31.15,0:04:33.46,Default,,0000,0000,0000,,Let's say I haven't opened\Nthis gate yet.
Dialogue: 0,0:04:33.46,0:04:35.03,Default,,0000,0000,0000,,So it's in its resting state.
Dialogue: 0,0:04:35.03,0:04:37.10,Default,,0000,0000,0000,,Our sodium potassium\Npumps are working.
Dialogue: 0,0:04:37.10,0:04:39.09,Default,,0000,0000,0000,,Things are leaking back and\Nforth, but it's staying at
Dialogue: 0,0:04:39.09,0:04:41.79,Default,,0000,0000,0000,,that minus 70 millivolts.
Dialogue: 0,0:04:41.79,0:04:46.77,Default,,0000,0000,0000,,So that right there is\Nminus 70 millivolts.
Dialogue: 0,0:04:46.77,0:04:51.11,Default,,0000,0000,0000,,Now as soon as this gate that's\Nway down some other
Dialogue: 0,0:04:51.11,0:04:53.77,Default,,0000,0000,0000,,part of the cell opens, what's\Ngoing to happen?
Dialogue: 0,0:04:53.77,0:04:55.91,Default,,0000,0000,0000,,And let's say that's the\Nonly thing that's open.
Dialogue: 0,0:04:55.91,0:04:58.37,Default,,0000,0000,0000,,So this, all of a sudden, is\Ngoing to become more positive.
Dialogue: 0,0:04:58.37,0:05:01.18,Default,,0000,0000,0000,,So positive charges that's\Nalready here-- so other
Dialogue: 0,0:05:01.18,0:05:07.48,Default,,0000,0000,0000,,positive charges, whether\Nthey're sodiums or potassiums,
Dialogue: 0,0:05:07.48,0:05:09.26,Default,,0000,0000,0000,,they're going to want to run\Naway from that point because
Dialogue: 0,0:05:09.26,0:05:11.48,Default,,0000,0000,0000,,this area hasn't had a flood\Nof positive things.
Dialogue: 0,0:05:11.48,0:05:13.84,Default,,0000,0000,0000,,So it's less positive\Nthan this over here.
Dialogue: 0,0:05:13.84,0:05:16.67,Default,,0000,0000,0000,,So maybe we have some potassiums\Nand maybe we have
Dialogue: 0,0:05:16.67,0:05:19.96,Default,,0000,0000,0000,,some sodiums. Everything is\Ngoing to want to move away
Dialogue: 0,0:05:19.96,0:05:23.31,Default,,0000,0000,0000,,from the place where\Nthis is opened.
Dialogue: 0,0:05:23.31,0:05:25.59,Default,,0000,0000,0000,,The charge is going to\Nwant to move away.
Dialogue: 0,0:05:25.59,0:05:28.91,Default,,0000,0000,0000,,So as soon as this happens, as\Nsoon as we open this gate,
Dialogue: 0,0:05:28.91,0:05:30.46,Default,,0000,0000,0000,,we're going to have a\Nmovement of positive
Dialogue: 0,0:05:30.46,0:05:31.23,Default,,0000,0000,0000,,charge in this direction.
Dialogue: 0,0:05:31.23,0:05:34.83,Default,,0000,0000,0000,,So all of a sudden-- this was\Nat minus 70 millivolts.
Dialogue: 0,0:05:34.83,0:05:37.24,Default,,0000,0000,0000,,So more positive charge\Nis coming its way.
Dialogue: 0,0:05:37.24,0:05:41.68,Default,,0000,0000,0000,,
Dialogue: 0,0:05:41.68,0:05:45.12,Default,,0000,0000,0000,,Almost immediately, it's going\Nto become less negative or
Dialogue: 0,0:05:45.12,0:05:46.47,Default,,0000,0000,0000,,more positive.
Dialogue: 0,0:05:46.47,0:05:48.59,Default,,0000,0000,0000,,The potential difference between\Nthis and this is going
Dialogue: 0,0:05:48.59,0:05:49.80,Default,,0000,0000,0000,,to become less.
Dialogue: 0,0:05:49.80,0:05:51.98,Default,,0000,0000,0000,,So this is this point\Nover here.
Dialogue: 0,0:05:51.98,0:05:57.90,Default,,0000,0000,0000,,Now if we took this point, if we\Ndid the same thing-- if we
Dialogue: 0,0:05:57.90,0:06:01.12,Default,,0000,0000,0000,,measured the voltage at this\Npoint right here, maybe it was
Dialogue: 0,0:06:01.12,0:06:06.15,Default,,0000,0000,0000,,at minus 70 millvolts, maybe a\Nfraction of a minute amount of
Dialogue: 0,0:06:06.15,0:06:09.56,Default,,0000,0000,0000,,time later, the positive charge\Nstarts affecting it so
Dialogue: 0,0:06:09.56,0:06:13.02,Default,,0000,0000,0000,,it becomes more positive, but\Nthe effect is diluted, right?
Dialogue: 0,0:06:13.02,0:06:14.66,Default,,0000,0000,0000,,Because these positive charges,\Nthey're going to
Dialogue: 0,0:06:14.66,0:06:16.24,Default,,0000,0000,0000,,radiate in every direction.
Dialogue: 0,0:06:16.24,0:06:17.41,Default,,0000,0000,0000,,So the effect is diluted.
Dialogue: 0,0:06:17.41,0:06:20.13,Default,,0000,0000,0000,,So the effect on this thing\Nis going to be less.
Dialogue: 0,0:06:20.13,0:06:21.86,Default,,0000,0000,0000,,It's going to become\Nless positive.
Dialogue: 0,0:06:21.86,0:06:26.16,Default,,0000,0000,0000,,So an electrotonic potential--\Nwhat happens is at one point
Dialogue: 0,0:06:26.16,0:06:30.39,Default,,0000,0000,0000,,in the cell, a gate opens,\Ncharge starts flooding in, and
Dialogue: 0,0:06:30.39,0:06:32.46,Default,,0000,0000,0000,,it starts affecting the\Npotential at other
Dialogue: 0,0:06:32.46,0:06:33.63,Default,,0000,0000,0000,,parts of the cell.
Dialogue: 0,0:06:33.63,0:06:40.97,Default,,0000,0000,0000,,But the positive of it is, it's\Nvery fast. As soon as
Dialogue: 0,0:06:40.97,0:06:41.82,Default,,0000,0000,0000,,this happens.
Dialogue: 0,0:06:41.82,0:06:50.00,Default,,0000,0000,0000,,further down the cell, it starts\Nbecoming more and more
Dialogue: 0,0:06:50.00,0:07:00.82,Default,,0000,0000,0000,,positive, but the further you\Ngo, the effect gets dissipated
Dialogue: 0,0:07:00.82,0:07:02.57,Default,,0000,0000,0000,,with distance.
Dialogue: 0,0:07:02.57,0:07:05.05,Default,,0000,0000,0000,,So if you care about speed,\Nyou'd want this
Dialogue: 0,0:07:05.05,0:07:06.24,Default,,0000,0000,0000,,electrotonic potential.
Dialogue: 0,0:07:06.24,0:07:08.62,Default,,0000,0000,0000,,As soon as it happens, it'll\Nstart affecting the rest of
Dialogue: 0,0:07:08.62,0:07:11.75,Default,,0000,0000,0000,,the cell, but if you wanted\Nthis potential change to
Dialogue: 0,0:07:11.75,0:07:14.66,Default,,0000,0000,0000,,travel over large distances--\Nfor example, let's say if we
Dialogue: 0,0:07:14.66,0:07:18.03,Default,,0000,0000,0000,,got all the way to this point of\Nthe neuron and we wanted to
Dialogue: 0,0:07:18.03,0:07:20.21,Default,,0000,0000,0000,,measure it, it might not\Nhave any impact.
Dialogue: 0,0:07:20.21,0:07:22.41,Default,,0000,0000,0000,,Maybe a little bit later, but\Nit's not having any impact
Dialogue: 0,0:07:22.41,0:07:24.92,Default,,0000,0000,0000,,because all of this gets diluted\Nby the time it gets--
Dialogue: 0,0:07:24.92,0:07:26.96,Default,,0000,0000,0000,,it's increasing the charge\Nthroughout the cell.
Dialogue: 0,0:07:26.96,0:07:30.20,Default,,0000,0000,0000,,So it's a impact far away from\Nthe initial place where the
Dialogue: 0,0:07:30.20,0:07:30.75,Default,,0000,0000,0000,,gate opened.
Dialogue: 0,0:07:30.75,0:07:32.24,Default,,0000,0000,0000,,It's going to be a lot less.
Dialogue: 0,0:07:32.24,0:07:36.11,Default,,0000,0000,0000,,So it's really not good for\Noperating over distance.
Dialogue: 0,0:07:36.11,0:07:38.04,Default,,0000,0000,0000,,Now let's try to figure\Nout what's going on
Dialogue: 0,0:07:38.04,0:07:40.08,Default,,0000,0000,0000,,with an action potential.
Dialogue: 0,0:07:40.08,0:07:43.31,Default,,0000,0000,0000,,And you might understand, this\Nmight involve more action.
Dialogue: 0,0:07:43.31,0:07:45.51,Default,,0000,0000,0000,,So let's start off with\Nthe same situation.
Dialogue: 0,0:07:45.51,0:07:51.50,Default,,0000,0000,0000,,We have a sodium gate that gets\Nopened by some stimulus.
Dialogue: 0,0:07:51.50,0:07:54.73,Default,,0000,0000,0000,,What I'm going to do-- let me\Ndraw two membranes here.
Dialogue: 0,0:07:54.73,0:07:55.98,Default,,0000,0000,0000,,So this is the outside.
Dialogue: 0,0:07:55.98,0:07:59.50,Default,,0000,0000,0000,,
Dialogue: 0,0:07:59.50,0:08:02.44,Default,,0000,0000,0000,,This is the inside.
Dialogue: 0,0:08:02.44,0:08:05.68,Default,,0000,0000,0000,,And let me draw-- maybe we're\Ndealing with a-- and we'll go
Dialogue: 0,0:08:05.68,0:08:06.27,Default,,0000,0000,0000,,in more detail.
Dialogue: 0,0:08:06.27,0:08:11.87,Default,,0000,0000,0000,,Maybe this is an axon or\Nsomething, but let me-- let's
Dialogue: 0,0:08:11.87,0:08:14.81,Default,,0000,0000,0000,,say we have another sodium\Ngate right here.
Dialogue: 0,0:08:14.81,0:08:18.81,Default,,0000,0000,0000,,
Dialogue: 0,0:08:18.81,0:08:21.70,Default,,0000,0000,0000,,And then they're alternating,\Nessentially.
Dialogue: 0,0:08:21.70,0:08:26.09,Default,,0000,0000,0000,,So they're alternating so then\NI have another sodium gate.
Dialogue: 0,0:08:26.09,0:08:38.52,Default,,0000,0000,0000,,
Dialogue: 0,0:08:38.52,0:08:39.98,Default,,0000,0000,0000,,I don't want to do\Na bunch of these.
Dialogue: 0,0:08:39.98,0:08:42.98,Default,,0000,0000,0000,,I think I just have to draw one\Nround of it for you to get
Dialogue: 0,0:08:42.98,0:08:44.73,Default,,0000,0000,0000,,what's going on.
Dialogue: 0,0:08:44.73,0:08:46.35,Default,,0000,0000,0000,,Let me draw another\Npotassium gate.
Dialogue: 0,0:08:46.35,0:08:52.14,Default,,0000,0000,0000,,
Dialogue: 0,0:08:52.14,0:08:54.29,Default,,0000,0000,0000,,And let's say that they\Nall start closed.
Dialogue: 0,0:08:54.29,0:08:56.24,Default,,0000,0000,0000,,So they're all in the\Nclosed position.
Dialogue: 0,0:08:56.24,0:08:58.75,Default,,0000,0000,0000,,Now let's say that this sodium\Ngate gets stimulated.
Dialogue: 0,0:08:58.75,0:09:00.00,Default,,0000,0000,0000,,It gets opened.
Dialogue: 0,0:09:00.00,0:09:03.22,Default,,0000,0000,0000,,
Dialogue: 0,0:09:03.22,0:09:05.74,Default,,0000,0000,0000,,Let's say that guy right\Nthere gets opened.
Dialogue: 0,0:09:05.74,0:09:07.67,Default,,0000,0000,0000,,It gets stimulated by something\Nto get opened.
Dialogue: 0,0:09:07.67,0:09:10.86,Default,,0000,0000,0000,,We'll talk about the things\Nthat-- let's say in particular
Dialogue: 0,0:09:10.86,0:09:20.16,Default,,0000,0000,0000,,this thing gets opened-- let's\Nsay the stimulus-- it has to
Dialogue: 0,0:09:20.16,0:09:21.21,Default,,0000,0000,0000,,be a certain voltage.
Dialogue: 0,0:09:21.21,0:09:26.17,Default,,0000,0000,0000,,And let's say they become open\Nwhen we are at minus 55
Dialogue: 0,0:09:26.17,0:09:27.42,Default,,0000,0000,0000,,millivolts.
Dialogue: 0,0:09:27.42,0:09:33.40,Default,,0000,0000,0000,,
Dialogue: 0,0:09:33.40,0:09:35.91,Default,,0000,0000,0000,,So when we're just in our\Nresting state, the potential
Dialogue: 0,0:09:35.91,0:09:38.27,Default,,0000,0000,0000,,difference between the inside of\Nthe cell and the outside is
Dialogue: 0,0:09:38.27,0:09:40.38,Default,,0000,0000,0000,,minus 70, so it's not\Ngoing to be open.
Dialogue: 0,0:09:40.38,0:09:43.42,Default,,0000,0000,0000,,It's going to be closed, but if\Nfor whatever reason, this
Dialogue: 0,0:09:43.42,0:09:47.52,Default,,0000,0000,0000,,becomes positive enough to get\Nto minus 55 millivolts, all of
Dialogue: 0,0:09:47.52,0:09:49.44,Default,,0000,0000,0000,,a sudden this thing\Nwill be open.
Dialogue: 0,0:09:49.44,0:09:52.73,Default,,0000,0000,0000,,Let's write a couple of other\Nrules that dictate what
Dialogue: 0,0:09:52.73,0:09:53.63,Default,,0000,0000,0000,,happens to this gate.
Dialogue: 0,0:09:53.63,0:09:57.88,Default,,0000,0000,0000,,Let's say it closes-- and these\Nare all rough numbers,
Dialogue: 0,0:09:57.88,0:10:01.26,Default,,0000,0000,0000,,but the main idea is for you\Nto get the general idea.
Dialogue: 0,0:10:01.26,0:10:10.91,Default,,0000,0000,0000,,Let's say it closes at--\NI don't know-- plus 35
Dialogue: 0,0:10:10.91,0:10:11.87,Default,,0000,0000,0000,,millivolts.
Dialogue: 0,0:10:11.87,0:10:20.30,Default,,0000,0000,0000,,And let's say that our potassium\Ngate opens at plus
Dialogue: 0,0:10:20.30,0:10:24.28,Default,,0000,0000,0000,,40 millvolts, just to give\Nan idea of things.
Dialogue: 0,0:10:24.28,0:10:33.11,Default,,0000,0000,0000,,Let's say it closes at--\NI don't know-- minus 80
Dialogue: 0,0:10:33.11,0:10:34.36,Default,,0000,0000,0000,,millivolts.
Dialogue: 0,0:10:34.36,0:10:36.21,Default,,0000,0000,0000,,
Dialogue: 0,0:10:36.21,0:10:37.01,Default,,0000,0000,0000,,So what's going to happen?
Dialogue: 0,0:10:37.01,0:10:40.04,Default,,0000,0000,0000,,Lets say that, for whatever\Nreason, the voltage here has
Dialogue: 0,0:10:40.04,0:10:41.62,Default,,0000,0000,0000,,now become minus 55.
Dialogue: 0,0:10:41.62,0:10:44.83,Default,,0000,0000,0000,,Let me do a chart just\Nlike I did down here.
Dialogue: 0,0:10:44.83,0:10:46.86,Default,,0000,0000,0000,,So I want to have space\Nto draw my chart.
Dialogue: 0,0:10:46.86,0:10:54.11,Default,,0000,0000,0000,,
Dialogue: 0,0:10:54.11,0:10:55.36,Default,,0000,0000,0000,,This is membrane voltage.
Dialogue: 0,0:10:55.36,0:11:00.37,Default,,0000,0000,0000,,
Dialogue: 0,0:11:00.37,0:11:03.08,Default,,0000,0000,0000,,And this is time down here.
Dialogue: 0,0:11:03.08,0:11:05.18,Default,,0000,0000,0000,,And let's say we're measuring\Nit-- let's say this is the
Dialogue: 0,0:11:05.18,0:11:08.79,Default,,0000,0000,0000,,membrane voltage at-- let's say\Nright by the sodium gate
Dialogue: 0,0:11:08.79,0:11:09.15,Default,,0000,0000,0000,,right here.
Dialogue: 0,0:11:09.15,0:11:10.35,Default,,0000,0000,0000,,So we're measuring this voltage
Dialogue: 0,0:11:10.35,0:11:11.48,Default,,0000,0000,0000,,across this right here.
Dialogue: 0,0:11:11.48,0:11:14.20,Default,,0000,0000,0000,,So if it's not stimulated any\Nway, we're just here,
Dialogue: 0,0:11:14.20,0:11:18.06,Default,,0000,0000,0000,,flatlining at minus 70\Nmillivolts-- and let's say
Dialogue: 0,0:11:18.06,0:11:19.83,Default,,0000,0000,0000,,some stimulus, for\Nwhatever reason,
Dialogue: 0,0:11:19.83,0:11:21.62,Default,,0000,0000,0000,,makes this more positive.
Dialogue: 0,0:11:21.62,0:11:24.95,Default,,0000,0000,0000,,Maybe it's some type of\Nelectrotonic effect that's
Dialogue: 0,0:11:24.95,0:11:26.43,Default,,0000,0000,0000,,making it more positive here.
Dialogue: 0,0:11:26.43,0:11:28.44,Default,,0000,0000,0000,,Maybe some positive charges\Nare floating by.
Dialogue: 0,0:11:28.44,0:11:30.86,Default,,0000,0000,0000,,So this becomes more positive.
Dialogue: 0,0:11:30.86,0:11:33.54,Default,,0000,0000,0000,,So let's say this becomes more\Npositive and then the ATP
Dialogue: 0,0:11:33.54,0:11:38.52,Default,,0000,0000,0000,,pumps-- the sodium potassium\Npumps pump it out so it
Dialogue: 0,0:11:38.52,0:11:41.78,Default,,0000,0000,0000,,doesn't get to the threshold of\Nminus 55, so then nothing
Dialogue: 0,0:11:41.78,0:11:42.62,Default,,0000,0000,0000,,will happen, right?
Dialogue: 0,0:11:42.62,0:11:43.64,Default,,0000,0000,0000,,It didn't get to\Nthe threshold.
Dialogue: 0,0:11:43.64,0:11:45.71,Default,,0000,0000,0000,,But then let's say there's\Nanother electrotonic or maybe
Dialogue: 0,0:11:45.71,0:11:47.95,Default,,0000,0000,0000,,a bunch of them and just there's\Na lot of positive
Dialogue: 0,0:11:47.95,0:11:54.48,Default,,0000,0000,0000,,charge here so we get to\Nthe minus 55 millvolts.
Dialogue: 0,0:11:54.48,0:11:55.96,Default,,0000,0000,0000,,Remember, when positive\Ncharge comes by,
Dialogue: 0,0:11:55.96,0:11:57.13,Default,,0000,0000,0000,,we become less negative.
Dialogue: 0,0:11:57.13,0:11:59.11,Default,,0000,0000,0000,,The potential difference\Nbecomes less negative.
Dialogue: 0,0:11:59.11,0:12:01.71,Default,,0000,0000,0000,,We get to that minus\N55 volts-- this
Dialogue: 0,0:12:01.71,0:12:03.95,Default,,0000,0000,0000,,thing opens then, right?
Dialogue: 0,0:12:03.95,0:12:05.20,Default,,0000,0000,0000,,This was closed before.
Dialogue: 0,0:12:05.20,0:12:07.38,Default,,0000,0000,0000,,It was closed when we were\Njust at minus 70.
Dialogue: 0,0:12:07.38,0:12:09.23,Default,,0000,0000,0000,,So let me write here.
Dialogue: 0,0:12:09.23,0:12:20.32,Default,,0000,0000,0000,,So at this point, our\Nsodium gate opens.
Dialogue: 0,0:12:20.32,0:12:23.04,Default,,0000,0000,0000,,Now, what's going to happen when\Nour sodium gate opens?
Dialogue: 0,0:12:23.04,0:12:25.78,Default,,0000,0000,0000,,When that opens-- we've seen\Nthis show before-- all the
Dialogue: 0,0:12:25.78,0:12:28.50,Default,,0000,0000,0000,,positively charged sodium is\Ngoing to go down there, both
Dialogue: 0,0:12:28.50,0:12:31.49,Default,,0000,0000,0000,,electric gradient and diffusion\Ngradient, and
Dialogue: 0,0:12:31.49,0:12:34.34,Default,,0000,0000,0000,,there's going to flood\Ninto the cell.
Dialogue: 0,0:12:34.34,0:12:36.20,Default,,0000,0000,0000,,There's so much sodium out\Nthere, it's so positive out
Dialogue: 0,0:12:36.20,0:12:37.91,Default,,0000,0000,0000,,there, they just want\Nto come in.
Dialogue: 0,0:12:37.91,0:12:41.35,Default,,0000,0000,0000,,So as soon as they hit that\Nthreshold, even though this
Dialogue: 0,0:12:41.35,0:12:44.91,Default,,0000,0000,0000,,might've only gotten us to minus\N55 or maybe minus 50,
Dialogue: 0,0:12:44.91,0:12:47.44,Default,,0000,0000,0000,,all of a sudden that gate opens\Nand we have all of this
Dialogue: 0,0:12:47.44,0:12:49.17,Default,,0000,0000,0000,,positive charge flooding\Ninto the cell.
Dialogue: 0,0:12:49.17,0:12:50.48,Default,,0000,0000,0000,,So the potential difference\Nbecomes
Dialogue: 0,0:12:50.48,0:12:51.80,Default,,0000,0000,0000,,much, much more positive.
Dialogue: 0,0:12:51.80,0:12:54.81,Default,,0000,0000,0000,,
Dialogue: 0,0:12:54.81,0:12:57.38,Default,,0000,0000,0000,,So they keep flooding in,\Nbecomes much, much more
Dialogue: 0,0:12:57.38,0:13:00.22,Default,,0000,0000,0000,,positive, but as it gets\Nmore positive, it
Dialogue: 0,0:13:00.22,0:13:15.34,Default,,0000,0000,0000,,closes at plus 35 millvolts.
Dialogue: 0,0:13:15.34,0:13:17.88,Default,,0000,0000,0000,,So let's say that we're dealing\Nhere-- let's say that
Dialogue: 0,0:13:17.88,0:13:21.31,Default,,0000,0000,0000,,this up here is plus\N35 millvolts.
Dialogue: 0,0:13:21.31,0:13:24.72,Default,,0000,0000,0000,,So here it closes and at the\Nsame time, that stuff I just
Dialogue: 0,0:13:24.72,0:13:30.55,Default,,0000,0000,0000,,deleted-- I set at plus 40\Nmillvolts-- or let's say at
Dialogue: 0,0:13:30.55,0:13:32.32,Default,,0000,0000,0000,,plus 35, just for the\Nsake of argument.
Dialogue: 0,0:13:32.32,0:13:34.84,Default,,0000,0000,0000,,Let's say at plus 45\Nmillvolts, our
Dialogue: 0,0:13:34.84,0:13:39.52,Default,,0000,0000,0000,,sodium gates open.
Dialogue: 0,0:13:39.52,0:13:40.65,Default,,0000,0000,0000,,So what's happened here?
Dialogue: 0,0:13:40.65,0:13:43.99,Default,,0000,0000,0000,,All of a sudden, we're at plus\N35 or maybe plus 40 millivolts
Dialogue: 0,0:13:43.99,0:13:47.43,Default,,0000,0000,0000,,so this is-- let's just say plus\N40, I think you get the
Dialogue: 0,0:13:47.43,0:13:51.84,Default,,0000,0000,0000,,idea either way so we'll say\Nplus 40-- either way.
Dialogue: 0,0:13:51.84,0:13:56.10,Default,,0000,0000,0000,,So at plus 40, this guy's\Ngoing to close.
Dialogue: 0,0:13:56.10,0:13:58.64,Default,,0000,0000,0000,,No more positive ions are coming\Nin, but now we are at
Dialogue: 0,0:13:58.64,0:14:01.34,Default,,0000,0000,0000,,more positive inside, at least\Nlocally at this point on the
Dialogue: 0,0:14:01.34,0:14:03.07,Default,,0000,0000,0000,,membrane, than we are outside.
Dialogue: 0,0:14:03.07,0:14:05.72,Default,,0000,0000,0000,,And so this gate will open.
Dialogue: 0,0:14:05.72,0:14:08.22,Default,,0000,0000,0000,,So then our sodium\Ngate will open.
Dialogue: 0,0:14:08.22,0:14:11.32,Default,,0000,0000,0000,,K-plus ion gate opens.
Dialogue: 0,0:14:11.32,0:14:12.72,Default,,0000,0000,0000,,Now when that opens,\Nwhat happens?
Dialogue: 0,0:14:12.72,0:14:15.80,Default,,0000,0000,0000,,We have all of these\Nsodium ions here.
Dialogue: 0,0:14:15.80,0:14:19.37,Default,,0000,0000,0000,,We already saw from the sodium\Npotassium pump that the
Dialogue: 0,0:14:19.37,0:14:22.51,Default,,0000,0000,0000,,potassium-- we have all of these\Npotassium ions here.
Dialogue: 0,0:14:22.51,0:14:25.15,Default,,0000,0000,0000,,We saw from the sodium potassium\Npump that it makes
Dialogue: 0,0:14:25.15,0:14:27.28,Default,,0000,0000,0000,,the sodium concentration on\Nthe outside higher and the
Dialogue: 0,0:14:27.28,0:14:30.30,Default,,0000,0000,0000,,potassium concentration\Non the inside higher.
Dialogue: 0,0:14:30.30,0:14:34.33,Default,,0000,0000,0000,,And now that we've gotten to\Nthis plus 40 millvolt range,
Dialogue: 0,0:14:34.33,0:14:37.14,Default,,0000,0000,0000,,we're also now more positive\Non the inside.
Dialogue: 0,0:14:37.14,0:14:38.36,Default,,0000,0000,0000,,So this opens.
Dialogue: 0,0:14:38.36,0:14:40.32,Default,,0000,0000,0000,,These guys want to escape\Nbecause there's
Dialogue: 0,0:14:40.32,0:14:42.20,Default,,0000,0000,0000,,less potassium outside.
Dialogue: 0,0:14:42.20,0:14:44.29,Default,,0000,0000,0000,,They want to go down their\Nconcentration gradient.
Dialogue: 0,0:14:44.29,0:14:45.94,Default,,0000,0000,0000,,It's also very positive\Non the inside.
Dialogue: 0,0:14:45.94,0:14:47.97,Default,,0000,0000,0000,,We're at plus 40 millvolts.
Dialogue: 0,0:14:47.97,0:14:49.48,Default,,0000,0000,0000,,So they also want to escape.
Dialogue: 0,0:14:49.48,0:14:51.50,Default,,0000,0000,0000,,So they start escaping\Nthe cells.
Dialogue: 0,0:14:51.50,0:14:54.35,Default,,0000,0000,0000,,So positive charges starts\Nexiting the cell from the
Dialogue: 0,0:14:54.35,0:14:56.21,Default,,0000,0000,0000,,inside to the outside.
Dialogue: 0,0:14:56.21,0:14:59.92,Default,,0000,0000,0000,,So we become less\Npositive again.
Dialogue: 0,0:14:59.92,0:15:01.55,Default,,0000,0000,0000,,So let me write what\Nhappens here.
Dialogue: 0,0:15:01.55,0:15:07.53,Default,,0000,0000,0000,,So at this point, our sodium\Ngate closes and our potassium
Dialogue: 0,0:15:07.53,0:15:09.14,Default,,0000,0000,0000,,gate opens.
Dialogue: 0,0:15:09.14,0:15:11.92,Default,,0000,0000,0000,,
Dialogue: 0,0:15:11.92,0:15:14.25,Default,,0000,0000,0000,,And then the positive charge\Nstarts flooding out of the
Dialogue: 0,0:15:14.25,0:15:18.30,Default,,0000,0000,0000,,cell again and maybe it'll\Novershoot because it's only
Dialogue: 0,0:15:18.30,0:15:21.67,Default,,0000,0000,0000,,going to close maybe once we\Nget to minus 80 millvolts.
Dialogue: 0,0:15:21.67,0:15:30.66,Default,,0000,0000,0000,,So maybe our potassium gate\Ncloses at minus 80.
Dialogue: 0,0:15:30.66,0:15:35.34,Default,,0000,0000,0000,,And then our sodium potassium\Npump might get us back to our
Dialogue: 0,0:15:35.34,0:15:36.55,Default,,0000,0000,0000,,minus 70 millvolts.
Dialogue: 0,0:15:36.55,0:15:40.94,Default,,0000,0000,0000,,So, this is what's happening\Njust at this point in the
Dialogue: 0,0:15:40.94,0:15:44.72,Default,,0000,0000,0000,,cell, just near that\Nfirst sodium gate.
Dialogue: 0,0:15:44.72,0:15:47.04,Default,,0000,0000,0000,,But what's going to happen\Nin general, right?
Dialogue: 0,0:15:47.04,0:15:49.68,Default,,0000,0000,0000,,As this became very positive--\Nwe went to 40
Dialogue: 0,0:15:49.68,0:15:51.34,Default,,0000,0000,0000,,millivolts over here.
Dialogue: 0,0:15:51.34,0:15:54.49,Default,,0000,0000,0000,,We went to 40 millvolts in\Nthis area of the cell.
Dialogue: 0,0:15:54.49,0:15:56.97,Default,,0000,0000,0000,,Because of-- I guess you could\Nalmost view it as a short term
Dialogue: 0,0:15:56.97,0:16:00.12,Default,,0000,0000,0000,,or very short distance\Nelectrotonic potential, this
Dialogue: 0,0:16:00.12,0:16:02.76,Default,,0000,0000,0000,,area is going to become\Nmore positive, right?
Dialogue: 0,0:16:02.76,0:16:03.91,Default,,0000,0000,0000,,This is going to become\Nmore positive.
Dialogue: 0,0:16:03.91,0:16:05.30,Default,,0000,0000,0000,,These positive charges\Nare going to go
Dialogue: 0,0:16:05.30,0:16:06.97,Default,,0000,0000,0000,,where it's less positive.
Dialogue: 0,0:16:06.97,0:16:09.04,Default,,0000,0000,0000,,So this is going to become\Nmore positive.
Dialogue: 0,0:16:09.04,0:16:11.97,Default,,0000,0000,0000,,This was at minus 70, but it's\Ngoing to become more positive.
Dialogue: 0,0:16:11.97,0:16:18.20,Default,,0000,0000,0000,,It'll go to minus 65, minus 60,\Nminus 55-- and then bam.
Dialogue: 0,0:16:18.20,0:16:19.78,Default,,0000,0000,0000,,This guy will get\Ntriggered again.
Dialogue: 0,0:16:19.78,0:16:22.06,Default,,0000,0000,0000,,Then this guy gets opened.
Dialogue: 0,0:16:22.06,0:16:23.44,Default,,0000,0000,0000,,Then this guy gets opened.
Dialogue: 0,0:16:23.44,0:16:25.43,Default,,0000,0000,0000,,Sodium floods in through here.
Dialogue: 0,0:16:25.43,0:16:27.84,Default,,0000,0000,0000,,So if you wanted to plot this\Nguy's, the potential
Dialogue: 0,0:16:27.84,0:16:33.24,Default,,0000,0000,0000,,difference of what's going on\Nacross this, this all happened
Dialogue: 0,0:16:33.24,0:16:36.63,Default,,0000,0000,0000,,as soon as-- maybe as soon as a\Nsodium started going in this
Dialogue: 0,0:16:36.63,0:16:41.44,Default,,0000,0000,0000,,first dude, the second guy-- he\Ngets triggered here because
Dialogue: 0,0:16:41.44,0:16:45.64,Default,,0000,0000,0000,,the second guy a little bit\Nlater in time-- because of all
Dialogue: 0,0:16:45.64,0:16:47.70,Default,,0000,0000,0000,,this flow a little bit to\Nthe left of him, his
Dialogue: 0,0:16:47.70,0:16:48.54,Default,,0000,0000,0000,,potential goes up.
Dialogue: 0,0:16:48.54,0:16:53.23,Default,,0000,0000,0000,,He gets triggered, same exact\Nthing happens to him, right?
Dialogue: 0,0:16:53.23,0:16:56.30,Default,,0000,0000,0000,,When the sodium flows in here,\Nbecomes really positive around
Dialogue: 0,0:16:56.30,0:16:59.63,Default,,0000,0000,0000,,here, that makes the cell\Naround here, the voltage
Dialogue: 0,0:16:59.63,0:17:01.18,Default,,0000,0000,0000,,around here, the charge around\Nhere a little bit more
Dialogue: 0,0:17:01.18,0:17:04.93,Default,,0000,0000,0000,,positive, triggers this next\Nsodium gate to open and then
Dialogue: 0,0:17:04.93,0:17:07.28,Default,,0000,0000,0000,,this whole same thing\Nhappens, same cycle.
Dialogue: 0,0:17:07.28,0:17:10.66,Default,,0000,0000,0000,,Then the potassium gates open to\Nmake it negative again, but
Dialogue: 0,0:17:10.66,0:17:12.96,Default,,0000,0000,0000,,by the time that's happened,\Nit's become positive over here
Dialogue: 0,0:17:12.96,0:17:14.63,Default,,0000,0000,0000,,to trigger another\Nsodium gate.
Dialogue: 0,0:17:14.63,0:17:18.07,Default,,0000,0000,0000,,So one after another, you have\Nthese sodium gates opening and
Dialogue: 0,0:17:18.07,0:17:20.84,Default,,0000,0000,0000,,closing, but it's transmitting\Nthat information, it's
Dialogue: 0,0:17:20.84,0:17:23.27,Default,,0000,0000,0000,,transmitting that potential\Nchange.
Dialogue: 0,0:17:23.27,0:17:25.13,Default,,0000,0000,0000,,So what's going on here?
Dialogue: 0,0:17:25.13,0:17:27.99,Default,,0000,0000,0000,,So this is slower and it\Nactually involves energy.
Dialogue: 0,0:17:27.99,0:17:32.20,Default,,0000,0000,0000,,So this was-- the electrotonic\Nwas very fast. This is slow.
Dialogue: 0,0:17:32.20,0:17:33.82,Default,,0000,0000,0000,,An action potential is slower.
Dialogue: 0,0:17:33.82,0:17:35.35,Default,,0000,0000,0000,,I don't want to say it's slow.
Dialogue: 0,0:17:35.35,0:17:38.40,Default,,0000,0000,0000,,It's slower because it has to\Ninvolve these opening and
Dialogue: 0,0:17:38.40,0:17:41.42,Default,,0000,0000,0000,,closing of gates and it\Nalso involves energy.
Dialogue: 0,0:17:41.42,0:17:43.28,Default,,0000,0000,0000,,It also requires more energy.
Dialogue: 0,0:17:43.28,0:17:47.88,Default,,0000,0000,0000,,
Dialogue: 0,0:17:47.88,0:17:50.44,Default,,0000,0000,0000,,And you're also going to have to\Nkeep changing the potential
Dialogue: 0,0:17:50.44,0:17:54.13,Default,,0000,0000,0000,,in your cell and you actively\Nhave your sodium potassium
Dialogue: 0,0:17:54.13,0:17:55.70,Default,,0000,0000,0000,,pumps being very active.
Dialogue: 0,0:17:55.70,0:17:56.77,Default,,0000,0000,0000,,But it's good.
Dialogue: 0,0:17:56.77,0:17:59.48,Default,,0000,0000,0000,,The positive is, it's good\Nat covering distance.
Dialogue: 0,0:17:59.48,0:18:02.33,Default,,0000,0000,0000,,
Dialogue: 0,0:18:02.33,0:18:03.82,Default,,0000,0000,0000,,When you have something like\Nthis-- we saw with the
Dialogue: 0,0:18:03.82,0:18:06.16,Default,,0000,0000,0000,,electrotonic, as we get further\Nand further away from
Dialogue: 0,0:18:06.16,0:18:09.12,Default,,0000,0000,0000,,where the stimulus happened,\Nthe change in potential
Dialogue: 0,0:18:09.12,0:18:10.32,Default,,0000,0000,0000,,becomes more and more\Ndissipated.
Dialogue: 0,0:18:10.32,0:18:12.08,Default,,0000,0000,0000,,It actually exponentially\Ndeclines.
Dialogue: 0,0:18:12.08,0:18:14.44,Default,,0000,0000,0000,,It becomes more and more\Ndissipated as we get further
Dialogue: 0,0:18:14.44,0:18:17.03,Default,,0000,0000,0000,,and further away so it's not\Ngood for long distance.
Dialogue: 0,0:18:17.03,0:18:20.60,Default,,0000,0000,0000,,This thing can just continue\Nforever because every time it
Dialogue: 0,0:18:20.60,0:18:23.17,Default,,0000,0000,0000,,stimulates the next gate, it's\Nlike we're starting all over
Dialogue: 0,0:18:23.17,0:18:26.94,Default,,0000,0000,0000,,again and so this gate-- it's\Ngoing to have a flood of ions
Dialogue: 0,0:18:26.94,0:18:30.55,Default,,0000,0000,0000,,come in and those ions are going\Nto make it a little less
Dialogue: 0,0:18:30.55,0:18:31.78,Default,,0000,0000,0000,,negative over here.
Dialogue: 0,0:18:31.78,0:18:33.11,Default,,0000,0000,0000,,Then the next gate's\Ngoing to open.
Dialogue: 0,0:18:33.11,0:18:34.75,Default,,0000,0000,0000,,We're going to have the cycle\Nover and over again.
Dialogue: 0,0:18:34.75,0:18:38.21,Default,,0000,0000,0000,,So this is really good for\Ntraveling long distances.
Dialogue: 0,0:18:38.21,0:18:40.85,Default,,0000,0000,0000,,So now we have really the\Nfoundation to understand
Dialogue: 0,0:18:40.85,0:18:43.88,Default,,0000,0000,0000,,exactly what's happening in a\Nneuron and I'm going to go
Dialogue: 0,0:18:43.88,0:18:46.33,Default,,0000,0000,0000,,over that in the next video to\Nshow you how electrotonic
Dialogue: 0,0:18:46.33,0:18:49.82,Default,,0000,0000,0000,,potentials and action potentials\Ncan combine to have
Dialogue: 0,0:18:49.82,0:18:51.97,Default,,0000,0000,0000,,a signal travel through\Na neuron.
Dialogue: 0,0:18:51.97,0:18:53.22,Default,,0000,0000,0000,,