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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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