WEBVTT

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We could have a debate about
what the most interesting cell

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in the human body is, but I
think easily the neuron would

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make the top five, and it's
not just because the cell

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itself is interesting.

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The fact that it essentially
makes up our brain and our

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nervous system and is
responsible for the thoughts

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and our feelings and maybe for
all of our sentience, I think,

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would easily make it the
top one or two cells.

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So what I want to do is first
to show you what a neuron

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looks like.

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And, of course, this is kind
of the perfect example.

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This isn't what all
neurons look like.

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And then we're going to talk
a little bit about how it

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performs its function, which is
essentially communication,

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essentially transmitting signals
across its length,

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depending on the signals
it receives.

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So if I were to draw
a neuron-- let me

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pick a better color.

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So let's say I have a neuron.

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It looks something like this.

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So in the middle you have your
soma and then from the soma--

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let me draw the nucleus.

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This is a nucleus, just like
any cell's nucleus.

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And then the soma's considered
the body of the neuron and

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then the neuron has these little
things sticking out

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from it that keep
branching off.

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Maybe they look something
like this.

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I don't want to spend too much
time just drawing the neuron,

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but you've probably seen
drawings like this before.

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And these branches off of the
soma of the neuron, off of its

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body, these are called
dendrites.

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They can keep splitting
off like that.

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I want to do a fairly reasonable
drawing so I'll

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spend a little time
doing that.

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So these right here, these
are dendrites.

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And these tend to be--
and nothing is

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always the case in biology.

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Sometimes different parts of
different cells perform other

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functions, but these tend to be
where the neuron receives

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its signal.

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And we'll talk more about what
it means to receive and

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transmit a signal in
this video and

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probably in the next few.

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So this is where it receives
the signal.

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So this is the dendrite.

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This right here is the soma.

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Soma means body.

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This is the body
of the neuron.

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And then we have kind of a--
you can almost view it as a

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tail of the neuron.

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It's called the axon.

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A neuron can be a reasonably
normal sized cell, although

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there is a huge range, but the
axons can be quite long.

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They could be short.

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Sometimes in the brain you might
have very small axons,

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but you might have axons that
go down the spinal column or

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that go along one of your
limbs-- or if you're talking

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about one of a dinosaur's
limbs.

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So the axon can actually
stretch several feet.

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Not all neurons' axons
are several feet,

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but they could be.

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And this is really where a lot
of the distance of the signal

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gets traveled.

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Let me draw the axon.

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So the axon will look
something like this.

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And at the end, it ends at the
axon terminal where it can

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connect to other dendrites or
maybe to other types of tissue

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or muscle if the point of this
neuron is to tell a muscle to

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do something.

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So at the end of the axon,
you have the axon

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terminal right there.

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I'll do my best to draw
it like that.

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Let me label it.

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So this is the axon.

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This is the axon terminal.

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And you'll sometimes hear the
word-- the point at which the

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soma or the body of the neuron
connects to the axon is as

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often referred to as the axon
hillock-- maybe you can kind

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of view it as kind of a lump.

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It starts to form the axon.

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And then we're going to talk
about how the impulses travel.

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And a huge part in what allows
them to travel efficiently are

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these insulating cells
around the axon.

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We're going to talk about this
in detail and how they

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actually work, but it's good
just to have the anatomical

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structure first. So these are
called Schwann cells and

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they're covering-- they make
up the myelin sheath.

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So this covering, this
insulation, at different

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intervals around the
axon, this is

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called the myelin sheath.

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So Schwann cells make up
the myelin sheath.

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I'll do one more
just like that.

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And then these little spaces
between the myelin sheath--

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just so we have all of the
terminology from-- so we know

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the entire anatomy of the
neuron-- these are called the

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nodes of Ranvier.

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I guess they're named
after Ranvier.

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Maybe he was the guy who looked
and saw they had these

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little slots here where you
don't have myelin sheath.

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So these are the nodes
of Ranvier.

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So the general idea, as I
mentioned, is that you get a

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signal here.

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We're going to talk more about
what the signal means-- and

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then that signal gets--
actually, the signals can be

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summed, so you might have one
little signal right there,

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another signal right there, and
then you'll have maybe a

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larger signal there and there--
and that the combined

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effects of these signals get
summed up and they travel to

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the hillock and if they're a
large enough, they're going to

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trigger an action potential on
the axon, which will cause a

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signal to travel down the
balance of the axon and then

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over here it might be connected
via synapses to

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other dendrites or muscles.

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And we'll talk more about
synapses and those might help

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trigger other things.

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So you're saying, what's
triggering these things here?

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Well, this could be the terminal
end of other neurons'

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axons, like in the brain.

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This could be some type
of sensory neuron.

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This could be on a taste bud
someplace, so a salt molecule

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somehow can trigger it or a
sugar molecule-- or this might

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be some type of sensor.

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It could be a whole bunch of
different things and we'll

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talk more about the different
types of neurons.

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