[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.00,0:00:00.61,Default,,0000,0000,0000,,
Dialogue: 0,0:00:00.61,0:00:03.62,Default,,0000,0000,0000,,We could have a debate about\Nwhat the most interesting cell
Dialogue: 0,0:00:03.62,0:00:07.54,Default,,0000,0000,0000,,in the human body is, but I\Nthink easily the neuron would
Dialogue: 0,0:00:07.54,0:00:10.81,Default,,0000,0000,0000,,make the top five, and it's\Nnot just because the cell
Dialogue: 0,0:00:10.81,0:00:11.83,Default,,0000,0000,0000,,itself is interesting.
Dialogue: 0,0:00:11.83,0:00:14.64,Default,,0000,0000,0000,,The fact that it essentially\Nmakes up our brain and our
Dialogue: 0,0:00:14.64,0:00:17.42,Default,,0000,0000,0000,,nervous system and is\Nresponsible for the thoughts
Dialogue: 0,0:00:17.42,0:00:22.01,Default,,0000,0000,0000,,and our feelings and maybe for\Nall of our sentience, I think,
Dialogue: 0,0:00:22.01,0:00:24.62,Default,,0000,0000,0000,,would easily make it the\Ntop one or two cells.
Dialogue: 0,0:00:24.62,0:00:26.92,Default,,0000,0000,0000,,So what I want to do is first\Nto show you what a neuron
Dialogue: 0,0:00:26.92,0:00:27.45,Default,,0000,0000,0000,,looks like.
Dialogue: 0,0:00:27.45,0:00:30.29,Default,,0000,0000,0000,,And, of course, this is kind\Nof the perfect example.
Dialogue: 0,0:00:30.29,0:00:31.67,Default,,0000,0000,0000,,This isn't what all\Nneurons look like.
Dialogue: 0,0:00:31.67,0:00:33.35,Default,,0000,0000,0000,,And then we're going to talk\Na little bit about how it
Dialogue: 0,0:00:33.35,0:00:37.00,Default,,0000,0000,0000,,performs its function, which is\Nessentially communication,
Dialogue: 0,0:00:37.00,0:00:40.76,Default,,0000,0000,0000,,essentially transmitting signals\Nacross its length,
Dialogue: 0,0:00:40.76,0:00:43.40,Default,,0000,0000,0000,,depending on the signals\Nit receives.
Dialogue: 0,0:00:43.40,0:00:45.47,Default,,0000,0000,0000,,So if I were to draw\Na neuron-- let me
Dialogue: 0,0:00:45.47,0:00:46.72,Default,,0000,0000,0000,,pick a better color.
Dialogue: 0,0:00:46.72,0:00:50.75,Default,,0000,0000,0000,,
Dialogue: 0,0:00:50.75,0:00:52.06,Default,,0000,0000,0000,,So let's say I have a neuron.
Dialogue: 0,0:00:52.06,0:00:53.12,Default,,0000,0000,0000,,It looks something like this.
Dialogue: 0,0:00:53.12,0:00:57.78,Default,,0000,0000,0000,,So in the middle you have your\Nsoma and then from the soma--
Dialogue: 0,0:00:57.78,0:01:00.85,Default,,0000,0000,0000,,let me draw the nucleus.
Dialogue: 0,0:01:00.85,0:01:03.39,Default,,0000,0000,0000,,This is a nucleus, just like\Nany cell's nucleus.
Dialogue: 0,0:01:03.39,0:01:07.19,Default,,0000,0000,0000,,And then the soma's considered\Nthe body of the neuron and
Dialogue: 0,0:01:07.19,0:01:09.26,Default,,0000,0000,0000,,then the neuron has these little\Nthings sticking out
Dialogue: 0,0:01:09.26,0:01:13.68,Default,,0000,0000,0000,,from it that keep\Nbranching off.
Dialogue: 0,0:01:13.68,0:01:16.08,Default,,0000,0000,0000,,Maybe they look something\Nlike this.
Dialogue: 0,0:01:16.08,0:01:18.91,Default,,0000,0000,0000,,I don't want to spend too much\Ntime just drawing the neuron,
Dialogue: 0,0:01:18.91,0:01:23.70,Default,,0000,0000,0000,,but you've probably seen\Ndrawings like this before.
Dialogue: 0,0:01:23.70,0:01:27.81,Default,,0000,0000,0000,,And these branches off of the\Nsoma of the neuron, off of its
Dialogue: 0,0:01:27.81,0:01:32.01,Default,,0000,0000,0000,,body, these are called\Ndendrites.
Dialogue: 0,0:01:32.01,0:01:34.46,Default,,0000,0000,0000,,They can keep splitting\Noff like that.
Dialogue: 0,0:01:34.46,0:01:36.99,Default,,0000,0000,0000,,I want to do a fairly reasonable\Ndrawing so I'll
Dialogue: 0,0:01:36.99,0:01:39.04,Default,,0000,0000,0000,,spend a little time\Ndoing that.
Dialogue: 0,0:01:39.04,0:01:43.00,Default,,0000,0000,0000,,
Dialogue: 0,0:01:43.00,0:01:46.14,Default,,0000,0000,0000,,So these right here, these\Nare dendrites.
Dialogue: 0,0:01:46.14,0:01:48.50,Default,,0000,0000,0000,,And these tend to be--\Nand nothing is
Dialogue: 0,0:01:48.50,0:01:49.86,Default,,0000,0000,0000,,always the case in biology.
Dialogue: 0,0:01:49.86,0:01:53.16,Default,,0000,0000,0000,,Sometimes different parts of\Ndifferent cells perform other
Dialogue: 0,0:01:53.16,0:01:56.94,Default,,0000,0000,0000,,functions, but these tend to be\Nwhere the neuron receives
Dialogue: 0,0:01:56.94,0:01:58.16,Default,,0000,0000,0000,,its signal.
Dialogue: 0,0:01:58.16,0:02:01.22,Default,,0000,0000,0000,,And we'll talk more about what\Nit means to receive and
Dialogue: 0,0:02:01.22,0:02:03.37,Default,,0000,0000,0000,,transmit a signal in\Nthis video and
Dialogue: 0,0:02:03.37,0:02:04.94,Default,,0000,0000,0000,,probably in the next few.
Dialogue: 0,0:02:04.94,0:02:09.63,Default,,0000,0000,0000,,So this is where it receives\Nthe signal.
Dialogue: 0,0:02:09.63,0:02:11.16,Default,,0000,0000,0000,,So this is the dendrite.
Dialogue: 0,0:02:11.16,0:02:13.03,Default,,0000,0000,0000,,This right here is the soma.
Dialogue: 0,0:02:13.03,0:02:14.39,Default,,0000,0000,0000,,Soma means body.
Dialogue: 0,0:02:14.39,0:02:17.13,Default,,0000,0000,0000,,This is the body\Nof the neuron.
Dialogue: 0,0:02:17.13,0:02:20.60,Default,,0000,0000,0000,,And then we have kind of a--\Nyou can almost view it as a
Dialogue: 0,0:02:20.60,0:02:22.10,Default,,0000,0000,0000,,tail of the neuron.
Dialogue: 0,0:02:22.10,0:02:23.35,Default,,0000,0000,0000,,It's called the axon.
Dialogue: 0,0:02:23.35,0:02:26.33,Default,,0000,0000,0000,,
Dialogue: 0,0:02:26.33,0:02:29.88,Default,,0000,0000,0000,,A neuron can be a reasonably\Nnormal sized cell, although
Dialogue: 0,0:02:29.88,0:02:32.82,Default,,0000,0000,0000,,there is a huge range, but the\Naxons can be quite long.
Dialogue: 0,0:02:32.82,0:02:33.87,Default,,0000,0000,0000,,They could be short.
Dialogue: 0,0:02:33.87,0:02:36.52,Default,,0000,0000,0000,,Sometimes in the brain you might\Nhave very small axons,
Dialogue: 0,0:02:36.52,0:02:39.61,Default,,0000,0000,0000,,but you might have axons that\Ngo down the spinal column or
Dialogue: 0,0:02:39.61,0:02:42.19,Default,,0000,0000,0000,,that go along one of your\Nlimbs-- or if you're talking
Dialogue: 0,0:02:42.19,0:02:44.24,Default,,0000,0000,0000,,about one of a dinosaur's\Nlimbs.
Dialogue: 0,0:02:44.24,0:02:47.19,Default,,0000,0000,0000,,So the axon can actually\Nstretch several feet.
Dialogue: 0,0:02:47.19,0:02:49.16,Default,,0000,0000,0000,,Not all neurons' axons\Nare several feet,
Dialogue: 0,0:02:49.16,0:02:50.15,Default,,0000,0000,0000,,but they could be.
Dialogue: 0,0:02:50.15,0:02:53.76,Default,,0000,0000,0000,,And this is really where a lot\Nof the distance of the signal
Dialogue: 0,0:02:53.76,0:02:55.10,Default,,0000,0000,0000,,gets traveled.
Dialogue: 0,0:02:55.10,0:02:58.19,Default,,0000,0000,0000,,Let me draw the axon.
Dialogue: 0,0:02:58.19,0:03:01.62,Default,,0000,0000,0000,,So the axon will look\Nsomething like this.
Dialogue: 0,0:03:01.62,0:03:06.08,Default,,0000,0000,0000,,And at the end, it ends at the\Naxon terminal where it can
Dialogue: 0,0:03:06.08,0:03:10.36,Default,,0000,0000,0000,,connect to other dendrites or\Nmaybe to other types of tissue
Dialogue: 0,0:03:10.36,0:03:13.99,Default,,0000,0000,0000,,or muscle if the point of this\Nneuron is to tell a muscle to
Dialogue: 0,0:03:13.99,0:03:14.91,Default,,0000,0000,0000,,do something.
Dialogue: 0,0:03:14.91,0:03:16.81,Default,,0000,0000,0000,,So at the end of the axon,\Nyou have the axon
Dialogue: 0,0:03:16.81,0:03:19.07,Default,,0000,0000,0000,,terminal right there.
Dialogue: 0,0:03:19.07,0:03:22.17,Default,,0000,0000,0000,,I'll do my best to draw\Nit like that.
Dialogue: 0,0:03:22.17,0:03:22.83,Default,,0000,0000,0000,,Let me label it.
Dialogue: 0,0:03:22.83,0:03:25.27,Default,,0000,0000,0000,,So this is the axon.
Dialogue: 0,0:03:25.27,0:03:26.53,Default,,0000,0000,0000,,This is the axon terminal.
Dialogue: 0,0:03:26.53,0:03:29.79,Default,,0000,0000,0000,,
Dialogue: 0,0:03:29.79,0:03:33.09,Default,,0000,0000,0000,,And you'll sometimes hear the\Nword-- the point at which the
Dialogue: 0,0:03:33.09,0:03:36.59,Default,,0000,0000,0000,,soma or the body of the neuron\Nconnects to the axon is as
Dialogue: 0,0:03:36.59,0:03:39.40,Default,,0000,0000,0000,,often referred to as the axon\Nhillock-- maybe you can kind
Dialogue: 0,0:03:39.40,0:03:40.38,Default,,0000,0000,0000,,of view it as kind of a lump.
Dialogue: 0,0:03:40.38,0:03:41.69,Default,,0000,0000,0000,,It starts to form the axon.
Dialogue: 0,0:03:41.69,0:03:46.74,Default,,0000,0000,0000,,
Dialogue: 0,0:03:46.74,0:03:54.61,Default,,0000,0000,0000,,And then we're going to talk\Nabout how the impulses travel.
Dialogue: 0,0:03:54.61,0:03:58.97,Default,,0000,0000,0000,,And a huge part in what allows\Nthem to travel efficiently are
Dialogue: 0,0:03:58.97,0:04:01.42,Default,,0000,0000,0000,,these insulating cells\Naround the axon.
Dialogue: 0,0:04:01.42,0:04:04.76,Default,,0000,0000,0000,,
Dialogue: 0,0:04:04.76,0:04:06.52,Default,,0000,0000,0000,,We're going to talk about this\Nin detail and how they
Dialogue: 0,0:04:06.52,0:04:09.23,Default,,0000,0000,0000,,actually work, but it's good\Njust to have the anatomical
Dialogue: 0,0:04:09.23,0:04:17.42,Default,,0000,0000,0000,,structure first. So these are\Ncalled Schwann cells and
Dialogue: 0,0:04:17.42,0:04:20.45,Default,,0000,0000,0000,,they're covering-- they make\Nup the myelin sheath.
Dialogue: 0,0:04:20.45,0:04:23.04,Default,,0000,0000,0000,,So this covering, this\Ninsulation, at different
Dialogue: 0,0:04:23.04,0:04:24.85,Default,,0000,0000,0000,,intervals around the\Naxon, this is
Dialogue: 0,0:04:24.85,0:04:26.71,Default,,0000,0000,0000,,called the myelin sheath.
Dialogue: 0,0:04:26.71,0:04:29.54,Default,,0000,0000,0000,,So Schwann cells make up\Nthe myelin sheath.
Dialogue: 0,0:04:29.54,0:04:31.01,Default,,0000,0000,0000,,I'll do one more\Njust like that.
Dialogue: 0,0:04:31.01,0:04:40.04,Default,,0000,0000,0000,,
Dialogue: 0,0:04:40.04,0:04:42.78,Default,,0000,0000,0000,,And then these little spaces\Nbetween the myelin sheath--
Dialogue: 0,0:04:42.78,0:04:46.39,Default,,0000,0000,0000,,just so we have all of the\Nterminology from-- so we know
Dialogue: 0,0:04:46.39,0:04:50.65,Default,,0000,0000,0000,,the entire anatomy of the\Nneuron-- these are called the
Dialogue: 0,0:04:50.65,0:04:51.90,Default,,0000,0000,0000,,nodes of Ranvier.
Dialogue: 0,0:04:51.90,0:04:56.62,Default,,0000,0000,0000,,
Dialogue: 0,0:04:56.62,0:04:57.95,Default,,0000,0000,0000,,I guess they're named\Nafter Ranvier.
Dialogue: 0,0:04:57.95,0:04:59.91,Default,,0000,0000,0000,,Maybe he was the guy who looked\Nand saw they had these
Dialogue: 0,0:04:59.91,0:05:02.81,Default,,0000,0000,0000,,little slots here where you\Ndon't have myelin sheath.
Dialogue: 0,0:05:02.81,0:05:05.28,Default,,0000,0000,0000,,So these are the nodes\Nof Ranvier.
Dialogue: 0,0:05:05.28,0:05:07.98,Default,,0000,0000,0000,,So the general idea, as I\Nmentioned, is that you get a
Dialogue: 0,0:05:07.98,0:05:08.86,Default,,0000,0000,0000,,signal here.
Dialogue: 0,0:05:08.86,0:05:11.07,Default,,0000,0000,0000,,We're going to talk more about\Nwhat the signal means-- and
Dialogue: 0,0:05:11.07,0:05:13.89,Default,,0000,0000,0000,,then that signal gets--\Nactually, the signals can be
Dialogue: 0,0:05:13.89,0:05:16.58,Default,,0000,0000,0000,,summed, so you might have one\Nlittle signal right there,
Dialogue: 0,0:05:16.58,0:05:19.45,Default,,0000,0000,0000,,another signal right there, and\Nthen you'll have maybe a
Dialogue: 0,0:05:19.45,0:05:23.01,Default,,0000,0000,0000,,larger signal there and there--\Nand that the combined
Dialogue: 0,0:05:23.01,0:05:26.78,Default,,0000,0000,0000,,effects of these signals get\Nsummed up and they travel to
Dialogue: 0,0:05:26.78,0:05:30.43,Default,,0000,0000,0000,,the hillock and if they're a\Nlarge enough, they're going to
Dialogue: 0,0:05:30.43,0:05:34.94,Default,,0000,0000,0000,,trigger an action potential on\Nthe axon, which will cause a
Dialogue: 0,0:05:34.94,0:05:38.28,Default,,0000,0000,0000,,signal to travel down the\Nbalance of the axon and then
Dialogue: 0,0:05:38.28,0:05:42.92,Default,,0000,0000,0000,,over here it might be connected\Nvia synapses to
Dialogue: 0,0:05:42.92,0:05:44.44,Default,,0000,0000,0000,,other dendrites or muscles.
Dialogue: 0,0:05:44.44,0:05:46.42,Default,,0000,0000,0000,,And we'll talk more about\Nsynapses and those might help
Dialogue: 0,0:05:46.42,0:05:47.79,Default,,0000,0000,0000,,trigger other things.
Dialogue: 0,0:05:47.79,0:05:49.77,Default,,0000,0000,0000,,So you're saying, what's\Ntriggering these things here?
Dialogue: 0,0:05:49.77,0:05:54.40,Default,,0000,0000,0000,,Well, this could be the terminal\Nend of other neurons'
Dialogue: 0,0:05:54.40,0:05:57.10,Default,,0000,0000,0000,,axons, like in the brain.
Dialogue: 0,0:05:57.10,0:05:58.91,Default,,0000,0000,0000,,This could be some type\Nof sensory neuron.
Dialogue: 0,0:05:58.91,0:06:02.49,Default,,0000,0000,0000,,This could be on a taste bud\Nsomeplace, so a salt molecule
Dialogue: 0,0:06:02.49,0:06:06.28,Default,,0000,0000,0000,,somehow can trigger it or a\Nsugar molecule-- or this might
Dialogue: 0,0:06:06.28,0:06:07.39,Default,,0000,0000,0000,,be some type of sensor.
Dialogue: 0,0:06:07.39,0:06:09.11,Default,,0000,0000,0000,,It could be a whole bunch of\Ndifferent things and we'll
Dialogue: 0,0:06:09.11,0:06:11.70,Default,,0000,0000,0000,,talk more about the different\Ntypes of neurons.
Dialogue: 0,0:06:11.70,0:06:12.95,Default,,0000,0000,0000,,