Anatomy of a Neuron

Introduction to the neuron and its anatomy

We could have a debate about
what the most interesting cell

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

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

itself is interesting.

The fact that it essentially
makes up our brain and our

nervous system and is
responsible for the thoughts

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

would easily make it the
top one or two cells.

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

looks like.

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

This isn't what all
neurons look like.

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

performs its function, which is
essentially communication,

essentially transmitting signals
across its length,

depending on the signals
it receives.

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

pick a better color.

So let's say I have a neuron.

It looks something like this.

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

let me draw the nucleus.

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

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

then the neuron has these little
things sticking out

from it that keep
branching off.

Maybe they look something
like this.

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

but you've probably seen
drawings like this before.

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

body, these are called
dendrites.

They can keep splitting
off like that.

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

spend a little time
doing that.

So these right here, these
are dendrites.

And these tend to be--
and nothing is

always the case in biology.

Sometimes different parts of
different cells perform other

functions, but these tend to be
where the neuron receives

its signal.

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

transmit a signal in
this video and

probably in the next few.

So this is where it receives
the signal.

So this is the dendrite.

This right here is the soma.

Soma means body.

This is the body
of the neuron.

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

tail of the neuron.

It's called the axon.

A neuron can be a reasonably
normal sized cell, although

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

They could be short.

Sometimes in the brain you might
have very small axons,

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

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

about one of a dinosaur's
limbs.

So the axon can actually
stretch several feet.

Not all neurons' axons
are several feet,

but they could be.

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

gets traveled.

Let me draw the axon.

So the axon will look
something like this.

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

connect to other dendrites or
maybe to other types of tissue

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

do something.

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

terminal right there.

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

Let me label it.

So this is the axon.

This is the axon terminal.

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

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

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

of view it as kind of a lump.

It starts to form the axon.

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

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

these insulating cells
around the axon.

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

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

structure first. So these are
called Schwann cells and

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

So this covering, this
insulation, at different

intervals around the
axon, this is

called the myelin sheath.

So Schwann cells make up
the myelin sheath.

I'll do one more
just like that.

And then these little spaces
between the myelin sheath--

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

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

nodes of Ranvier.

I guess they're named
after Ranvier.

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

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

So these are the nodes
of Ranvier.

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

signal here.

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

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

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

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

larger signal there and there--
and that the combined

effects of these signals get
summed up and they travel to

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

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

signal to travel down the
balance of the axon and then

over here it might be connected
via synapses to

other dendrites or muscles.

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

trigger other things.

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

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

axons, like in the brain.

This could be some type
of sensory neuron.

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

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

be some type of sensor.

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

talk more about the different
types of neurons.