[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.89,0:00:03.82,Default,,0000,0000,0000,,So let's talk about\Npacemaker cells.
Dialogue: 0,0:00:03.82,0:00:07.48,Default,,0000,0000,0000,,I'm going to actually\Ndraw out the action
Dialogue: 0,0:00:07.48,0:00:09.09,Default,,0000,0000,0000,,potential for a pacemaker cell.
Dialogue: 0,0:00:09.09,0:00:12.62,Default,,0000,0000,0000,,And remember, this\Nis time over here.
Dialogue: 0,0:00:12.62,0:00:14.99,Default,,0000,0000,0000,,And let's do it with millivolts.
Dialogue: 0,0:00:14.99,0:00:18.89,Default,,0000,0000,0000,,This is positive up here\Nand negative down here.
Dialogue: 0,0:00:18.89,0:00:22.77,Default,,0000,0000,0000,,Now, our pacemaker\Ncells, let's specifically
Dialogue: 0,0:00:22.77,0:00:25.60,Default,,0000,0000,0000,,talk about the ones\Nin the SA node.
Dialogue: 0,0:00:25.60,0:00:28.00,Default,,0000,0000,0000,,So this is our SA\Nnode action potential,
Dialogue: 0,0:00:28.00,0:00:31.74,Default,,0000,0000,0000,,and you know it starts out\Nkind of negative and creeps up.
Dialogue: 0,0:00:31.74,0:00:34.17,Default,,0000,0000,0000,,And that's mainly\Nbecause of sodium,
Dialogue: 0,0:00:34.17,0:00:36.69,Default,,0000,0000,0000,,sodium leaking into the cell.
Dialogue: 0,0:00:36.69,0:00:40.97,Default,,0000,0000,0000,,And other ions are present as\Nwell, but that's the major ion.
Dialogue: 0,0:00:40.97,0:00:42.83,Default,,0000,0000,0000,,Now it gets up to\Nthis point, right,
Dialogue: 0,0:00:42.83,0:00:45.20,Default,,0000,0000,0000,,where I'm drawing\Nkind of a threshold.
Dialogue: 0,0:00:45.20,0:00:46.90,Default,,0000,0000,0000,,And this threshold is for what?
Dialogue: 0,0:00:46.90,0:00:50.48,Default,,0000,0000,0000,,Well, this is kind\Nof this dashed line
Dialogue: 0,0:00:50.48,0:00:52.83,Default,,0000,0000,0000,,represents the point\Nat which calcium
Dialogue: 0,0:00:52.83,0:00:54.53,Default,,0000,0000,0000,,channels start to open up.
Dialogue: 0,0:00:54.53,0:00:56.60,Default,,0000,0000,0000,,And so they open up\Nand causes the cell
Dialogue: 0,0:00:56.60,0:00:58.17,Default,,0000,0000,0000,,to become even more positive.
Dialogue: 0,0:00:58.17,0:00:59.54,Default,,0000,0000,0000,,So it was already\Ngoing positive,
Dialogue: 0,0:00:59.54,0:01:01.36,Default,,0000,0000,0000,,it's going to go\Neven more positive.
Dialogue: 0,0:01:01.36,0:01:03.74,Default,,0000,0000,0000,,And it's going to get\Nto about that point.
Dialogue: 0,0:01:03.74,0:01:07.68,Default,,0000,0000,0000,,And then finally, at this\Npoint, those calcium channels,
Dialogue: 0,0:01:07.68,0:01:10.23,Default,,0000,0000,0000,,those voltage gated calcium\Nchannels, close down
Dialogue: 0,0:01:10.23,0:01:11.89,Default,,0000,0000,0000,,and potassium channels open up.
Dialogue: 0,0:01:11.89,0:01:15.81,Default,,0000,0000,0000,,Which causes the\Nmembrane to repolarize.
Dialogue: 0,0:01:15.81,0:01:18.59,Default,,0000,0000,0000,,So these are the three\Nphases we've talked about.
Dialogue: 0,0:01:18.59,0:01:22.18,Default,,0000,0000,0000,,This is phase 4, we\Nnumbered it as phase 4.
Dialogue: 0,0:01:22.18,0:01:24.75,Default,,0000,0000,0000,,This is phase 0,\Nand this is phase 1.
Dialogue: 0,0:01:24.75,0:01:28.01,Default,,0000,0000,0000,,These are the three\Nphases we discussed.
Dialogue: 0,0:01:28.01,0:01:30.01,Default,,0000,0000,0000,,So now let's think about\Nit a little bit harder.
Dialogue: 0,0:01:30.01,0:01:33.20,Default,,0000,0000,0000,,Let's say that we\Nview this, and I
Dialogue: 0,0:01:33.20,0:01:35.08,Default,,0000,0000,0000,,think that's a pretty\Nreasonable thing to do,
Dialogue: 0,0:01:35.08,0:01:37.42,Default,,0000,0000,0000,,view this as the heartbeat.
Dialogue: 0,0:01:37.42,0:01:39.03,Default,,0000,0000,0000,,This is one heartbeat, right?
Dialogue: 0,0:01:39.03,0:01:41.82,Default,,0000,0000,0000,,And you know if we were to\Nkeep this picture going,
Dialogue: 0,0:01:41.82,0:01:43.65,Default,,0000,0000,0000,,basically you would get\Nanother one of these
Dialogue: 0,0:01:43.65,0:01:46.28,Default,,0000,0000,0000,,and another one of these, and it\Nwould just basically continue.
Dialogue: 0,0:01:46.28,0:01:48.77,Default,,0000,0000,0000,,And this is what our heart\Nrate then looks like, right?
Dialogue: 0,0:01:48.77,0:01:51.79,Default,,0000,0000,0000,,If you were just to look at\Na strip over, let's say, two,
Dialogue: 0,0:01:51.79,0:01:53.16,Default,,0000,0000,0000,,three minutes, it\Nwould basically
Dialogue: 0,0:01:53.16,0:01:56.87,Default,,0000,0000,0000,,be just one after another\Nof these kinds of action
Dialogue: 0,0:01:56.87,0:01:59.65,Default,,0000,0000,0000,,potentials kind of\Nstacked on each other.
Dialogue: 0,0:01:59.65,0:02:02.60,Default,,0000,0000,0000,,So now if I was to take this\Nheartbeat and shorten it,
Dialogue: 0,0:02:02.60,0:02:05.08,Default,,0000,0000,0000,,let's say I was to make\Nit instead of ending where
Dialogue: 0,0:02:05.08,0:02:07.78,Default,,0000,0000,0000,,it does, let's say I\Nended it right there.
Dialogue: 0,0:02:07.78,0:02:11.14,Default,,0000,0000,0000,,So that this whole thing kind\Nof gets brought this way.
Dialogue: 0,0:02:11.14,0:02:16.52,Default,,0000,0000,0000,,Well, it would crunch down on\Nmy action potential in phase 4.
Dialogue: 0,0:02:16.52,0:02:18.15,Default,,0000,0000,0000,,But what would\Nthat mean exactly?
Dialogue: 0,0:02:18.15,0:02:20.36,Default,,0000,0000,0000,,I mean you think, well, so\Nwhat, so it's a little bit
Dialogue: 0,0:02:20.36,0:02:22.84,Default,,0000,0000,0000,,more crunched down, happens\Na little faster, so what?
Dialogue: 0,0:02:22.84,0:02:25.14,Default,,0000,0000,0000,,Well, what it means,\Nif you think about it,
Dialogue: 0,0:02:25.14,0:02:27.53,Default,,0000,0000,0000,,is if the heart beats are\Nstacking on top of each other,
Dialogue: 0,0:02:27.53,0:02:30.91,Default,,0000,0000,0000,,if you make the heartbeat\Nitself a little bit quicker,
Dialogue: 0,0:02:30.91,0:02:34.65,Default,,0000,0000,0000,,meaning takes less\Ntime to finish,
Dialogue: 0,0:02:34.65,0:02:36.70,Default,,0000,0000,0000,,then the next one can\Nstart a little bit early,
Dialogue: 0,0:02:36.70,0:02:38.38,Default,,0000,0000,0000,,and then that one\Nwill finish early,
Dialogue: 0,0:02:38.38,0:02:39.85,Default,,0000,0000,0000,,and the next one\Nwill start early,
Dialogue: 0,0:02:39.85,0:02:41.43,Default,,0000,0000,0000,,and basically, at\Nthe end of a minute,
Dialogue: 0,0:02:41.43,0:02:44.21,Default,,0000,0000,0000,,you'll have more\Nheartbeats fit in.
Dialogue: 0,0:02:44.21,0:02:47.11,Default,,0000,0000,0000,,So by having a shorter\Nheartbeat, what you're really
Dialogue: 0,0:02:47.11,0:02:50.01,Default,,0000,0000,0000,,saying is that you're\Nincreasing the heart rate.
Dialogue: 0,0:02:50.01,0:02:53.54,Default,,0000,0000,0000,,The number of heartbeats\Nin a minute goes up.
Dialogue: 0,0:02:53.54,0:02:55.00,Default,,0000,0000,0000,,So that's actually\Npretty powerful.
Dialogue: 0,0:02:55.00,0:02:57.82,Default,,0000,0000,0000,,Because we think about\Nheart rates all the time,
Dialogue: 0,0:02:57.82,0:02:59.72,Default,,0000,0000,0000,,but rarely do we think\Nabout exactly what
Dialogue: 0,0:02:59.72,0:03:01.84,Default,,0000,0000,0000,,that means for each\Nindividual heartbeat.
Dialogue: 0,0:03:01.84,0:03:04.71,Default,,0000,0000,0000,,And what it means is that\Neach heartbeat goes quicker.
Dialogue: 0,0:03:04.71,0:03:06.94,Default,,0000,0000,0000,,Now, the opposite\Nis true too, right?
Dialogue: 0,0:03:06.94,0:03:09.08,Default,,0000,0000,0000,,You could imagine actually\Nextending this out.
Dialogue: 0,0:03:09.08,0:03:11.76,Default,,0000,0000,0000,,Let's say the heartbeat actually\Ngoes a little bit longer.
Dialogue: 0,0:03:11.76,0:03:13.67,Default,,0000,0000,0000,,You could extend\Nit out that way.
Dialogue: 0,0:03:13.67,0:03:15.36,Default,,0000,0000,0000,,And if the heartbeat\Ngoes longer,
Dialogue: 0,0:03:15.36,0:03:19.51,Default,,0000,0000,0000,,then that means that you can get\Nfewer packed into one minute.
Dialogue: 0,0:03:19.51,0:03:21.01,Default,,0000,0000,0000,,And that means that\Nyou're basically
Dialogue: 0,0:03:21.01,0:03:23.84,Default,,0000,0000,0000,,saying that you're\Nreducing the heart rate.
Dialogue: 0,0:03:23.84,0:03:28.12,Default,,0000,0000,0000,,So when I say I'm increasing\Nor decreasing the heart rate,
Dialogue: 0,0:03:28.12,0:03:31.89,Default,,0000,0000,0000,,really what I'm trying to\Nsay is that I'm shortening
Dialogue: 0,0:03:31.89,0:03:35.31,Default,,0000,0000,0000,,or lengthening the heartbeat\Nso that's actually,
Dialogue: 0,0:03:35.31,0:03:37.77,Default,,0000,0000,0000,,I think, a pretty powerful idea.
Dialogue: 0,0:03:37.77,0:03:39.67,Default,,0000,0000,0000,,Now let's take it\Na step further.
Dialogue: 0,0:03:39.67,0:03:42.36,Default,,0000,0000,0000,,Let's actually do a\Nlittle thought experiment.
Dialogue: 0,0:03:42.36,0:03:45.76,Default,,0000,0000,0000,,Let's imagine that this is\N1/10 of a second right here.
Dialogue: 0,0:03:45.76,0:03:47.78,Default,,0000,0000,0000,,1/10 of a second.
Dialogue: 0,0:03:47.78,0:03:50.54,Default,,0000,0000,0000,,And it may not be\Nexactly 1/10 of a second,
Dialogue: 0,0:03:50.54,0:03:52.67,Default,,0000,0000,0000,,but let's just imagine it is.
Dialogue: 0,0:03:52.67,0:03:56.34,Default,,0000,0000,0000,,And let's say I wanted to take\Na look at our cell at this point
Dialogue: 0,0:03:56.34,0:03:59.82,Default,,0000,0000,0000,,because that's where\N1/10 of a second has hit.
Dialogue: 0,0:03:59.82,0:04:01.13,Default,,0000,0000,0000,,What would our cell look like?
Dialogue: 0,0:04:01.13,0:04:04.52,Default,,0000,0000,0000,,Let me actually just make a\Nlittle bit of space on a canvas
Dialogue: 0,0:04:04.52,0:04:07.69,Default,,0000,0000,0000,,and draw out what our cell might\Nlook like at 1/10 of a second.
Dialogue: 0,0:04:07.69,0:04:11.92,Default,,0000,0000,0000,,And just to make sure I keep\Neveryone on the same page,
Dialogue: 0,0:04:11.92,0:04:14.99,Default,,0000,0000,0000,,this is what's happening\Nin our pacemaker cell
Dialogue: 0,0:04:14.99,0:04:17.07,Default,,0000,0000,0000,,at 1/10 of a second.
Dialogue: 0,0:04:17.07,0:04:19.18,Default,,0000,0000,0000,,So at this point,\Nyou have a cell.
Dialogue: 0,0:04:19.18,0:04:21.16,Default,,0000,0000,0000,,Let me actually draw\Na blown up version
Dialogue: 0,0:04:21.16,0:04:24.68,Default,,0000,0000,0000,,of our cell that\Nmight look like this.
Dialogue: 0,0:04:24.68,0:04:28.10,Default,,0000,0000,0000,,And this cell is going\Nto have ions flowing in,
Dialogue: 0,0:04:28.10,0:04:30.49,Default,,0000,0000,0000,,it's going to have, let's\Nsay, sodium coming in.
Dialogue: 0,0:04:30.49,0:04:32.84,Default,,0000,0000,0000,,And we know that this\Nis the dominant ion.
Dialogue: 0,0:04:32.84,0:04:35.96,Default,,0000,0000,0000,,So let me draw, let's\Nsay, a few of them,
Dialogue: 0,0:04:35.96,0:04:39.18,Default,,0000,0000,0000,,kind of gushing into our cell.
Dialogue: 0,0:04:39.18,0:04:42.17,Default,,0000,0000,0000,,And we also have some\Nother ions coming in.
Dialogue: 0,0:04:42.17,0:04:43.88,Default,,0000,0000,0000,,And you might think,\Nwell, wait a second,
Dialogue: 0,0:04:43.88,0:04:46.33,Default,,0000,0000,0000,,I thought only sodium comes in.
Dialogue: 0,0:04:46.33,0:04:48.48,Default,,0000,0000,0000,,And that's definitely\Nnot the case.
Dialogue: 0,0:04:48.48,0:04:50.70,Default,,0000,0000,0000,,Even though sodium\Nis the dominant ion,
Dialogue: 0,0:04:50.70,0:04:55.51,Default,,0000,0000,0000,,meaning the cell is mostly\Npermeable to sodium,
Dialogue: 0,0:04:55.51,0:04:59.41,Default,,0000,0000,0000,,calcium is actually leaking in,\Nand a little bit of potassium
Dialogue: 0,0:04:59.41,0:05:00.56,Default,,0000,0000,0000,,might be leaking out.
Dialogue: 0,0:05:00.56,0:05:03.83,Default,,0000,0000,0000,,So you have other ions moving\Nback and forth, as well.
Dialogue: 0,0:05:03.83,0:05:05.71,Default,,0000,0000,0000,,Even though, in\Nthis case, sodium
Dialogue: 0,0:05:05.71,0:05:10.73,Default,,0000,0000,0000,,is the major contributor\Nto the membrane potential.
Dialogue: 0,0:05:10.73,0:05:14.35,Default,,0000,0000,0000,,So if that's the case, now\Nlet's take another look
Dialogue: 0,0:05:14.35,0:05:16.37,Default,,0000,0000,0000,,at the membrane.
Dialogue: 0,0:05:16.37,0:05:17.99,Default,,0000,0000,0000,,Now let's take a look\Nat this membrane,
Dialogue: 0,0:05:17.99,0:05:22.62,Default,,0000,0000,0000,,and let me show you\Nwhat might be out here.
Dialogue: 0,0:05:22.62,0:05:25.10,Default,,0000,0000,0000,,You've got some\Nreceptors on this side.
Dialogue: 0,0:05:25.10,0:05:30.80,Default,,0000,0000,0000,,And those receptors are\Nfor a neurotransmitter.
Dialogue: 0,0:05:30.80,0:05:33.49,Default,,0000,0000,0000,,So there's actually\Nnerves that come down
Dialogue: 0,0:05:33.49,0:05:37.76,Default,,0000,0000,0000,,and land right on\Nour pacemaker cell.
Dialogue: 0,0:05:37.76,0:05:40.37,Default,,0000,0000,0000,,And these are the\Nsympathetic nerves.
Dialogue: 0,0:05:43.65,0:05:49.29,Default,,0000,0000,0000,,And these nerves are releasing\Nsome neurotransmitter.
Dialogue: 0,0:05:49.29,0:05:50.96,Default,,0000,0000,0000,,And this\Nneurotransmitter, I'm just
Dialogue: 0,0:05:50.96,0:05:55.13,Default,,0000,0000,0000,,going to try to label as\NI go, is norepinephrine.
Dialogue: 0,0:05:55.13,0:05:56.97,Default,,0000,0000,0000,,Norepi sometimes it's called.
Dialogue: 0,0:05:59.82,0:06:03.74,Default,,0000,0000,0000,,So norepinephrine comes and\Nlands on these receptors
Dialogue: 0,0:06:03.74,0:06:06.58,Default,,0000,0000,0000,,and is going to cause\Na signal into the cell.
Dialogue: 0,0:06:06.58,0:06:08.85,Default,,0000,0000,0000,,And it's going to\Nbasically tell the cell
Dialogue: 0,0:06:08.85,0:06:11.55,Default,,0000,0000,0000,,to be permeable to these ions.
Dialogue: 0,0:06:11.55,0:06:15.20,Default,,0000,0000,0000,,Allow these ions to flow\Nacross the membrane.
Dialogue: 0,0:06:15.20,0:06:17.54,Default,,0000,0000,0000,,So they say, OK, fair enough.
Dialogue: 0,0:06:17.54,0:06:21.26,Default,,0000,0000,0000,,Now on the other side, you've\Ngot another set of receptors.
Dialogue: 0,0:06:21.26,0:06:22.63,Default,,0000,0000,0000,,And, of course,\Nit's not actually
Dialogue: 0,0:06:22.63,0:06:24.80,Default,,0000,0000,0000,,divided by one\Nside and the other.
Dialogue: 0,0:06:24.80,0:06:27.29,Default,,0000,0000,0000,,I'm just doing it\Nto kind of represent
Dialogue: 0,0:06:27.29,0:06:32.05,Default,,0000,0000,0000,,an idea, which is that\Non this other receptor,
Dialogue: 0,0:06:32.05,0:06:38.01,Default,,0000,0000,0000,,you've got other kinds of\Nneurotransmitters landing.
Dialogue: 0,0:06:38.01,0:06:40.85,Default,,0000,0000,0000,,And these right here,\Nare acetylcholine.
Dialogue: 0,0:06:44.53,0:06:49.23,Default,,0000,0000,0000,,Now, acetylcholine is also\Ngoing to send a signal down here
Dialogue: 0,0:06:49.23,0:06:56.10,Default,,0000,0000,0000,,and this signal is coming\Nfrom parasympathetic nerves.
Dialogue: 0,0:06:56.10,0:06:58.66,Default,,0000,0000,0000,,You might have heard of\Nsympathetic and parasympathetic
Dialogue: 0,0:06:58.66,0:06:59.46,Default,,0000,0000,0000,,nerves.
Dialogue: 0,0:06:59.46,0:07:03.45,Default,,0000,0000,0000,,These are both part of the\Nautonomic nerve system.
Dialogue: 0,0:07:03.45,0:07:05.01,Default,,0000,0000,0000,,And the parasympathetic\Nnerves are
Dialogue: 0,0:07:05.01,0:07:06.51,Default,,0000,0000,0000,,sending kind of an\Nopposite message.
Dialogue: 0,0:07:06.51,0:07:09.33,Default,,0000,0000,0000,,They're saying to this\Ncell, well, wait a second,
Dialogue: 0,0:07:09.33,0:07:11.81,Default,,0000,0000,0000,,don't allow so\Nmuch permeability.
Dialogue: 0,0:07:11.81,0:07:14.85,Default,,0000,0000,0000,,Don't allow so many ions\Nto go back and forth
Dialogue: 0,0:07:14.85,0:07:17.28,Default,,0000,0000,0000,,across your membrane.
Dialogue: 0,0:07:17.28,0:07:20.29,Default,,0000,0000,0000,,So opposite messages\Ncoming in, and as it
Dialogue: 0,0:07:20.29,0:07:23.64,Default,,0000,0000,0000,,turns out, that they kind of\Nbalance and offset each other.
Dialogue: 0,0:07:23.64,0:07:25.10,Default,,0000,0000,0000,,And so you get what\NI've shown you.
Dialogue: 0,0:07:25.10,0:07:28.21,Default,,0000,0000,0000,,You get some sodium coming\Nin, a little bit of calcium,
Dialogue: 0,0:07:28.21,0:07:31.16,Default,,0000,0000,0000,,and a little bit of\Npotassium leaving.
Dialogue: 0,0:07:31.16,0:07:34.61,Default,,0000,0000,0000,,Now, if I was to actually show\Nyou now what could happen.
Dialogue: 0,0:07:34.61,0:07:38.38,Default,,0000,0000,0000,,Let me try to take a shortcut\Nhere and do a little cut,
Dialogue: 0,0:07:38.38,0:07:40.14,Default,,0000,0000,0000,,paste.
Dialogue: 0,0:07:40.14,0:07:42.41,Default,,0000,0000,0000,,Imagine that this happens.
Dialogue: 0,0:07:42.41,0:07:43.42,Default,,0000,0000,0000,,Something like this.
Dialogue: 0,0:07:43.42,0:07:46.99,Default,,0000,0000,0000,,Let's show you, I'm going to\Nhave to move this canvas up
Dialogue: 0,0:07:46.99,0:07:49.08,Default,,0000,0000,0000,,a little bit.
Dialogue: 0,0:07:49.08,0:07:53.34,Default,,0000,0000,0000,,But let's say now, you\Nhave more sympathetics.
Dialogue: 0,0:07:53.34,0:07:56.03,Default,,0000,0000,0000,,Let's say you have more\Nsympathetics coming in
Dialogue: 0,0:07:56.03,0:07:59.31,Default,,0000,0000,0000,,than parasympathetics, then you\Nmight get something like this.
Dialogue: 0,0:07:59.31,0:08:02.15,Default,,0000,0000,0000,,Where instead of just a little\Nbit of neurotransmitters
Dialogue: 0,0:08:02.15,0:08:04.24,Default,,0000,0000,0000,,here, let's say\Nyou get a lot more.
Dialogue: 0,0:08:04.24,0:08:07.39,Default,,0000,0000,0000,,And let's say now this\Nreceptor is also firing,
Dialogue: 0,0:08:07.39,0:08:10.48,Default,,0000,0000,0000,,and let's say you get\Na little bit of firing
Dialogue: 0,0:08:10.48,0:08:12.12,Default,,0000,0000,0000,,from this receptor.
Dialogue: 0,0:08:12.12,0:08:15.94,Default,,0000,0000,0000,,Well, now you get all three\Nreceptors on the left,
Dialogue: 0,0:08:15.94,0:08:19.69,Default,,0000,0000,0000,,and that really outbalances\Nthe one receptor on the right.
Dialogue: 0,0:08:19.69,0:08:21.80,Default,,0000,0000,0000,,So your sympathetic drive\Nhere, you could say,
Dialogue: 0,0:08:21.80,0:08:24.76,Default,,0000,0000,0000,,is much stronger than your\Nparasympathetic drive.
Dialogue: 0,0:08:24.76,0:08:26.93,Default,,0000,0000,0000,,And if that's the case, if\Nyour sympathetic drive is
Dialogue: 0,0:08:26.93,0:08:29.86,Default,,0000,0000,0000,,much stronger, than\Nwhat's going to happen
Dialogue: 0,0:08:29.86,0:08:35.35,Default,,0000,0000,0000,,is you're going to have more\Nsodium coming into the cell.
Dialogue: 0,0:08:35.35,0:08:37.98,Default,,0000,0000,0000,,Because, again, the\Nsympathetics are
Dialogue: 0,0:08:37.98,0:08:41.65,Default,,0000,0000,0000,,trying to get more\Nion permeability.
Dialogue: 0,0:08:41.65,0:08:45.29,Default,,0000,0000,0000,,So you have a lot\Nmore sodium gushing in
Dialogue: 0,0:08:45.29,0:08:47.87,Default,,0000,0000,0000,,and you'll get a little\Nbit of extra calcium, too.
Dialogue: 0,0:08:47.87,0:08:50.64,Default,,0000,0000,0000,,You'll get more\Ncalcium here, too.
Dialogue: 0,0:08:50.64,0:08:53.27,Default,,0000,0000,0000,,And you'll get more\Npotassium leaving the cell.
Dialogue: 0,0:08:53.27,0:08:57.91,Default,,0000,0000,0000,,So basically sympathetics are\Ngoing to cause all of the ions
Dialogue: 0,0:08:57.91,0:09:00.63,Default,,0000,0000,0000,,to increase in the\Ndirection of movement.
Dialogue: 0,0:09:00.63,0:09:02.83,Default,,0000,0000,0000,,So you're going to get\Nmore sodium to come in,
Dialogue: 0,0:09:02.83,0:09:04.66,Default,,0000,0000,0000,,you're going to get\Nmore calcium to come in,
Dialogue: 0,0:09:04.66,0:09:07.62,Default,,0000,0000,0000,,and you're going to get\Nmore potassium to leave.
Dialogue: 0,0:09:07.62,0:09:08.56,Default,,0000,0000,0000,,So that's interesting.
Dialogue: 0,0:09:08.56,0:09:10.72,Default,,0000,0000,0000,,And let's actually\Njust keep that in mind.
Dialogue: 0,0:09:10.72,0:09:12.51,Default,,0000,0000,0000,,I'm actually going to\Ndo this one more time
Dialogue: 0,0:09:12.51,0:09:14.88,Default,,0000,0000,0000,,and show you what could happen\Nif the opposite were true.
Dialogue: 0,0:09:14.88,0:09:19.80,Default,,0000,0000,0000,,Let's say that in this case, you\Nhad more parasympathetic drive.
Dialogue: 0,0:09:19.80,0:09:23.84,Default,,0000,0000,0000,,So let's say here, you have\Nnow, in this third scenario--
Dialogue: 0,0:09:23.84,0:09:26.79,Default,,0000,0000,0000,,remember the first scenario was\Nkind of the baseline scenario,
Dialogue: 0,0:09:26.79,0:09:28.59,Default,,0000,0000,0000,,and this third\Nscenario now, let's say
Dialogue: 0,0:09:28.59,0:09:33.39,Default,,0000,0000,0000,,you have more acetylcholine\Nfilling up these receptors.
Dialogue: 0,0:09:33.39,0:09:37.67,Default,,0000,0000,0000,,And that's outdoing what the\Nsympathetic nerves are doing.
Dialogue: 0,0:09:37.67,0:09:41.24,Default,,0000,0000,0000,,So now you've got a lot more\Nparasympathetic stimulation.
Dialogue: 0,0:09:41.24,0:09:43.86,Default,,0000,0000,0000,,Well, now this cell is\Ngoing to think, OK, well,
Dialogue: 0,0:09:43.86,0:09:47.57,Default,,0000,0000,0000,,the parasympathetics don't\Nwant as much ion movement,
Dialogue: 0,0:09:47.57,0:09:49.84,Default,,0000,0000,0000,,so less sodium.
Dialogue: 0,0:09:49.84,0:09:51.56,Default,,0000,0000,0000,,Again, this is all\Nin 1/10 of a second,
Dialogue: 0,0:09:51.56,0:09:54.24,Default,,0000,0000,0000,,so if you just catch the\Ncell at 1/10 of a second,
Dialogue: 0,0:09:54.24,0:09:55.90,Default,,0000,0000,0000,,less sodium has moved in.
Dialogue: 0,0:09:55.90,0:09:59.29,Default,,0000,0000,0000,,Maybe less calcium\Nhas gotten in.
Dialogue: 0,0:09:59.29,0:10:02.34,Default,,0000,0000,0000,,And maybe less\Npotassium has left.
Dialogue: 0,0:10:02.34,0:10:05.08,Default,,0000,0000,0000,,So if you look at 1/10 of\Na second, the pictures,
Dialogue: 0,0:10:05.08,0:10:07.68,Default,,0000,0000,0000,,the snapshots are\Nreally, really different.
Dialogue: 0,0:10:07.68,0:10:10.14,Default,,0000,0000,0000,,So in both scenarios,\Nsympathetics
Dialogue: 0,0:10:10.14,0:10:12.99,Default,,0000,0000,0000,,and parasympathetics,\Nit's the same ions.
Dialogue: 0,0:10:12.99,0:10:15.11,Default,,0000,0000,0000,,They're moving in\Nthe same direction,
Dialogue: 0,0:10:15.11,0:10:19.05,Default,,0000,0000,0000,,but what we're looking at\Nis the amount of charge
Dialogue: 0,0:10:19.05,0:10:22.16,Default,,0000,0000,0000,,that's flowing over\Na period of time.
Dialogue: 0,0:10:22.16,0:10:24.24,Default,,0000,0000,0000,,And sometimes you might\Neven use the word current.
Dialogue: 0,0:10:24.24,0:10:25.72,Default,,0000,0000,0000,,You might say,\Nwell, sympathetics
Dialogue: 0,0:10:25.72,0:10:28.87,Default,,0000,0000,0000,,are increasing the current,\Nand parasympathetics
Dialogue: 0,0:10:28.87,0:10:32.20,Default,,0000,0000,0000,,are decreasing the current,\Nthe amount of charge that's
Dialogue: 0,0:10:32.20,0:10:34.83,Default,,0000,0000,0000,,moving over a period of time.
Dialogue: 0,0:10:34.83,0:10:37.28,Default,,0000,0000,0000,,So how would this actually\Nlook on our figure?
Dialogue: 0,0:10:37.28,0:10:38.78,Default,,0000,0000,0000,,So we drew a figure at the top.
Dialogue: 0,0:10:38.78,0:10:40.81,Default,,0000,0000,0000,,How would this actually\Nlook on this figure?
Dialogue: 0,0:10:40.81,0:10:43.47,Default,,0000,0000,0000,,Well, I'm going to use\Nthe colors red and green
Dialogue: 0,0:10:43.47,0:10:47.92,Default,,0000,0000,0000,,because that's kind of what\Nwe've gotten into using here.
Dialogue: 0,0:10:47.92,0:10:51.74,Default,,0000,0000,0000,,So green, remember that was\Nour sympathetic scenario, well,
Dialogue: 0,0:10:51.74,0:10:53.36,Default,,0000,0000,0000,,what that's going to\Ndo is that's going
Dialogue: 0,0:10:53.36,0:10:59.16,Default,,0000,0000,0000,,to basically increase the\Namount of charge rushing in.
Dialogue: 0,0:10:59.16,0:11:03.01,Default,,0000,0000,0000,,And at 1/10 of a second,\Nyou've got more positive ions
Dialogue: 0,0:11:03.01,0:11:04.00,Default,,0000,0000,0000,,in the cell.
Dialogue: 0,0:11:04.00,0:11:05.73,Default,,0000,0000,0000,,So, let's say, at\Nthat point, you've
Dialogue: 0,0:11:05.73,0:11:07.66,Default,,0000,0000,0000,,actually already hit threshold.
Dialogue: 0,0:11:07.66,0:11:10.93,Default,,0000,0000,0000,,And you might now fire\Nin an action potential.
Dialogue: 0,0:11:10.93,0:11:14.20,Default,,0000,0000,0000,,And it will come\Ndown just as before.
Dialogue: 0,0:11:14.20,0:11:17.03,Default,,0000,0000,0000,,And your heart rate\Nis basically going
Dialogue: 0,0:11:17.03,0:11:21.09,Default,,0000,0000,0000,,to go up because you've\Nshortened the heartbeat.
Dialogue: 0,0:11:21.09,0:11:23.81,Default,,0000,0000,0000,,And the opposite's going to\Nhappen with parasympathetics.
Dialogue: 0,0:11:23.81,0:11:25.43,Default,,0000,0000,0000,,So with parasympathetics,\Nyou're going
Dialogue: 0,0:11:25.43,0:11:29.84,Default,,0000,0000,0000,,to have a longer time to\Nget to that threshold.
Dialogue: 0,0:11:29.84,0:11:32.74,Default,,0000,0000,0000,,Because, again, it's\Nat 1/10 of a second,
Dialogue: 0,0:11:32.74,0:11:35.92,Default,,0000,0000,0000,,only a little bit of sodium\Nand calcium were inside,
Dialogue: 0,0:11:35.92,0:11:38.31,Default,,0000,0000,0000,,and only a little bit\Nof potassium had left.
Dialogue: 0,0:11:38.31,0:11:42.23,Default,,0000,0000,0000,,And you're going to have\Nroughly the same looking
Dialogue: 0,0:11:42.23,0:11:45.53,Default,,0000,0000,0000,,action potential as before.
Dialogue: 0,0:11:45.53,0:11:48.71,Default,,0000,0000,0000,,And you've gotten a much\Nlower heart rate now
Dialogue: 0,0:11:48.71,0:11:51.06,Default,,0000,0000,0000,,because the heartbeat\Nis much longer.
Dialogue: 0,0:11:51.06,0:11:54.39,Default,,0000,0000,0000,,So you can see that the amount\Nof current that's flowing
Dialogue: 0,0:11:54.39,0:11:55.17,Default,,0000,0000,0000,,is changing.
Dialogue: 0,0:11:55.17,0:11:58.86,Default,,0000,0000,0000,,And so, really, we're tweaking\Nphase 4 with our sympathetics
Dialogue: 0,0:11:58.86,0:12:02.58,Default,,0000,0000,0000,,and parasympathetics to\Nchange our heart rate.