MARINE DIAMOND: So
let's continue now,
with our spinal nerves.
And I wanted to introduce
the two motor components
in your ventral root.
Your ventral root,
if you recall,
was coming from your
anterior horn cell.
It was coming up here.
And this would be
our ventral root.
But I wanted you
to know that there
was something other
than just what we
call the alpha efferent.
It's the somatic motor component
coming from the anterior horn.
So this would be an
alpha efferent fiber
coming from that cell.
But there are gamma
efferents which are smaller.
And they also will go out
over your ventral root,
and go out with your
spinal nerve eventually.
And these are muscle spindles.
Has anybody ever seen a muscle
spindle in a tissue sample?
They're beautifully designed.
What are they for?
They're a stretch receptor.
But I just wanted you
to know that there
were two kinds of fibers
going in your ventral root.
Now, let's take a
cross section of our--
we can just put it here--
a cross section
of a spinal nerve.
And we'll start with
just the nerve fibers.
We're creating a
cross-section of them.
And these then would
be nerve fibers.
And they'll be covered
with connective tissue.
The connective tissue
surrounding a single nerve
fiber is called what?
You know?
Endoneurium.
Endoneurium.
So around each one of these
single fibers that could either
be afferent or efferent--
so our rust color
is the endoneurium.
And these are gathered together
with connective tissue, which
will gather them in bundles.
So what are you
going to call these?
Perineurium.
Right?
Perineurium just around again.
Perineurium.
And then the whole
group of fibers
are surrounded with
heavy connective tissue
giving us the what?
Epineurium.
Right.
So when you are dissecting
and you pick up a nerve,
you're picking up out here.
This whole thing then could
be just a cross section.
Let's just take the ulnar nerve.
So you see how well
it's defined in here.
When you study
pharmacology, certain drugs
will penetrate some of these.
Some will not.
So one learns
different things about
this particular structure.
So now, another term I want
to introduce-- the term plexi.
Have you heard of plexus, plexi?
You have several major plexi.
I'm only to mention two.
Can I take-- no
I'll wait for that.
So plexi, that's plural.
Plexus-- singular.
We have the brachial plexus, and
we have the lumbosacral plexus.
Lumbo sacral.
So now, you know where they are.
Why do we need these plexi?
Because we've added appendages.
So when the nerves
are going to go out,
they're going to recombine
as they leave the cord,
and form a plexus.
There are many divisions
of these plexi.
But we're just going to
introduce the concept to you.
So we've recombined spinal
nerves to make plexi.
So roughly we could say, let's
go C5, C6, C7, and C8, and T1.
Those are all coming
out individually,
but they can combine
into different nerves.
And the one that I'm
going to give you
will combine all of them.
It's going to go out like this.
Like this.
Like this.
This and this.
And give us a single nerve.
That's a plexi.
And that particular nerve
that I've developed here,
will be the radial nerve.
This obviously is in
our brachial plexus
because the three combined for
the brachial plexus C5 to T1.
And the radial nerve will go to
the extensors of the forearm--
extensors forearm.
So what's going to
happen when you cut it?
How are you going to know that
you've cut the radial nerve?
Tell somebody to salute.
Instead of doing this.
They'll do this.
Right?
You have what's called wrist
drop because you have nothing
to extend your wrist.
Right?
You've cut the radial nerve.
So a wrist drop if you cut.
The medial nerve on
the anterior surface
is also a combination
of C5 through T1.
And the medial nerve then,
will be dealing with flexors.
Does anybody ever
damage the medial nerve?
Some people will use
their hand for a hammer.
Medial nerve comes right
to the surface there--
will damage it.
What can't you do if your
medial nerve is damaged?
You can't make a fist--
a complete fist.
Can't make fist.
Actually since sometimes these
two [? latter ?] fingers are
not involved, [? but ?]
you can't do at least with
the first three.
But it gives you an idea of
why the have to combine these.
As these muscle cells
are migrating out
they form a different pattern.
They can't just do like
the thoracic cavity does--
just come straight around.
Right?
All right.
So that's our plexi.
The next we want to
do, is what happens
when you injure the nervous
system or a spinal nerve.
Has anybody injured
a spinal nerve?
Anybody cut them?
Nobody?
So this will be injury.
Now, the degree of degeneration
after you've cut a nerve
will depend on location.
Degree of degeneration
depend on location.
What do I mean by that?
Here, I have my nerve
cell with its axon.
And I cut it a A. What
happens when I cut at A?
Usually, the cell will die.
You're that close to
insulting your soma.
If I cut peripherally
or distilly at B,
we have several
things that can occur.
But what we're going to do
is follow first degeneration
and then regeneration.
So let's take a--
we'll make a new
nerve cell here.
And we're going to cut it.
We'll do it this way.
And we have myelin around it.
We'll just put on two
segments of myelin.
And we'll put some down here.
It will be on the fiber.
On the proximal
end of cut, we'll
have degeneration back to
the first node of Ranvier.
Degeneration back to the
first node of Ranvier.
And we know that we've
damaged this proximal part
by changes that are taking
place in the cell body.
So in the cell
body, in the soma,
the process of chromatolysis--
have you heard of chromatolysis?
Chromatolysis occurs--
chromatolysis.
This is in the
injured nerve cell.
And what do we see
with chromatolysis?
How do we know if this
particular nerve is damaged?
Well, first, the soma
or will take in water.
So it will swell--
soma swells.
That swelling will then
displace the nucleus.
So the nucleus
becomes eccentric--
nucleus eccentric.
And the nissl substance,
which is normally
fairly equally distributed
throughout the cytoplasm,
the nissl substance then,
will go to the periphery
with the swelling--
nissl to periphery.
All of this is taking
place in the soma.
So your nerve cell,
instead of looking
this way with nissl
dispersed all throughout,
you'll have a cell which
is considerably larger.
The nissl will be over
here in the periphery.
And the nucleus will be
eccentric over to the side.
So three characteristics of
knowing whether you've got
a healthy nerve cell or not.
Now, as we come back
to our cut, we've
taken this part, our proximal
part, chromatolyis here,
degeneration back to the
first note of Ranvier.
In the distal segment--
what will happen in
the distal segment?
Well, the first place
the axon will break up.
Just little beads axon left.
So the axon breaks up.
And the Schwann cells multiply.
So you're going to increase
the number of Schwann cells
out here so that they've got
a Schwann cell lined tube.
Schwann cells multiply.
So if you don't have any
scar tissue where you're cut
was, as the soma recovers
they will send out sprouts
from the axon.
Across the gap, one of them
can find your Schwann tube
and go down and make
contact with the target.
So with regeneration the
proximal axon sproutts,
and one of them will
find the Schwahn tube.
Sometimes you have
trouble, and they
get all mixed up in the gap
here, and you form a neuroma.
None of them can
find the pathway.
Sometimes if scar tissue comes
and builds scar across here,
a surgeon can cut out the
scar and put in a Dacron tube
so when the sprout comes
it'll follow that little tube
and get into the proper channel.
So there are ways to help.
How fast is it traveling once
it's in the Schwann tube?
It can travel as fast as 3
to 4 millimeters per day.
That's fast.
What's the most rapid growth
of a nerve fiber that we know--
that I know at least
in the animal kingdom?
In the deer antler,
you know the deer
shed their antlers every year.
And they've got to get the
velvet all re innervated.
It's highly sensitive.
It can go about five
millimeters there.
I always think
someday somebody is
going to go analyze and
find out what substance
is in the ganglion that
allows that to grow so fast,
and use it with human beings
when they damage their cord
because it's really something.
Someday somebody will do it.
All right.
So that gives you an idea of
what we mean by regeneration.
But let's say that
you've cut a neuron
but you don't get chromatolysis.
Why not?
You're given some
slides to study.
And you have no
chromatolysis, yet you
know you've cut the neuron.
So if I have, why no
chromatolyis after nerve cut?
Well, here we have
our nerves cell.
Here its axon.
Here's some myelin.
Very diachromatically placed.
And this nerve is cut.
And you still have a
perfectly healthy nerve cell.
Why?
Because axons can
send out branches.
Branches of axons
come out just where
they can between Schwann
cells in a node of Ranvier.
So I'm going to
bring out a branch
from this axon here going in
the same direction as the parent
axon.
But this one is cut.
But we have what's
known as a collateral.
A collateral-- that's
a branch from an axon.
And it can go in
the same direction
or it can go back up here.
Can ascend or descend.
But that's the reason you could
have no chromatolysis when
you've cut a parent nerve
fiber because of collaterals.
Did you know that the greatest
input to your cerebral cortex
are collaterals?
From pyramidal cells that
are leaving your cortex,
this is cortex, its
got cell going out.
But it's also sending
back up collaterals.
The greatest input
from all it's coming
all over your body,
the greatest input
is from pyramidal cell axons.
Collaterals-- pyramidal cell
collaterals, which are axons
but they're coming
from a parent cell.
So you can figure that
one out for the dynamics.
Reinforcement-- what's it doing?
Is that what happens when
we repeat constantly?
Who knows.
But I thought that
was fascinating.
And that was only found
maybe 10 or 15 years ago.
Not too long ago.
So now, let's go back
to our spinal cord,
and look at white matter.
Last time we had formed what
was happening to our gray matter
in the spinal cord.
Spinal cord.
White matter.
So we've seen them come
from the marginal layer.
We know it's going to be
peripheral in the cord.
So all around the periphery
will be white matter.
We'll find that
it's divided into,
let's put P, L, and A. So
the white matter is grouped
into what we call funiculi.
White matter forms groups of
fibers, which are funiculi.
And the funiculi are broken down
into specific functional groups
called for fasciculi.
Fasciculi are functional
groups within funiculi.
So as I showed a slide last
time of multiple sclerosis,
it was up here in our
posterior funiculi.
This is the posterior
funiculus between the midline
and over here.
So posterior funiculus.
So when you're reading slides,
you're saying degeneration.
You don't just say
a white matter.
You say posterior funiculus.
You know exactly where you are.
So this one's going to
be the lateral funiculus.
So what does that
allow this one to be?
Anterior.
Really smart, yes.
Anterior funiculus.
But they're useful landmarks.
And I'm going to use
one for an illustration.
I'm just going to take since
the same sensory modality is
in the whole of
the posterior, I'm
going to take the
posterior to give you
an illustration of what a
fasciculus is and a funiculus.
So if I take my
cord again, They'll
be two fasciculi in the
posterior funiculus.
So medial will have the
fasciculus gracilis.
Fasciculus gracilis.
fasciculus gracilis.
What does gracile mean?
Pardon?
Slender.
It's a real complement
to give somebody--
how gracile you look today.
Right?
It's slender.
So it's a slender one.
The lateral one is
fasciculus cuneatus--
fasciculus cuneatus.
And cunea means wedge shaped.
Don't want to call anybody that.
But this is wedge shaped.
So it gives you an example that
here we have two fasciculi.
Why separate?
Because the
fasciculus gracilis is
coming from the lower
part of the body,
lower body, which makes sense.
As you're bringing in
sensory information,
you bring it over
to the midline,
so as we get to
the upper body it
can come to the outer portion.
So this would be upper body.
What kind of sensations
is it bringing?
What we call conscious
proprioception.
Right?
Now, think of your feet.
You could see them down there.
You're not moving.
You know exactly where they are.
Proprioception--
position in space.
Right?
When we get to the
cerebellum, you'll
get unconscious
proprioception that goes
on every time you take a step.
Gotta know where your feet are.
But you don't want to be
thinking about them so you turn
it over to your cerebellum.
But when you want
to think about it,
that's a conscious
proprioception.
So the sensory modality
carried by these fibers
up to the cortex is
conscious proprioception.
Very important.
Try yourself out at
night when it's dark.
See it if you now where
the light switch is.
All these kind of things.
It's fun.
It's good training for you.
So that gives you an
idea of what fasciculi
are within the fasciculus.
Now, the whole white matter
is filled with fasciculi.
And we're going to take
an ascending pathway
today, and a
descending pathway just
so you get the general idea.
And I'm going to give
it to you very briefly.
Not all the ramifications.
Just so you see the basics.
I'm taking pain and temperature
as my ascending pathway.
It's so beautifully laid out and
embryologically how it develops
is amazing.
So we're going to take
an ascending pathway.
And the sensory modalities
will be pain and temperature.
That's how you get pain up to
consciousness because we've
got to come from the
periphery out here
and get up to your
cerebral cortex.
When you took your
shower this morning,
how do you know whether it was
the right temperature or not?
If you didn't have this
pathway, you'll scald yourself.
Right?
This is letting you know
pain and temperature.
Why pain?
Well, pain sensing is
essential to your survival.
Letting you know when you've
got something that's too much.
Essential to survival.
But it's also an enemy.
When you get to be older, and
you've got terminal cancer,
and no medication will
handle the pain, when
you have intractable
pain, pain is an enemy.
With intractable pain-- you're
lucky, you get a little problem
and you take Tylenol
or something.
But there are times when
nothing that we know
will get rid of it.
What they'll do is they'll
cut the dorsal roots
if they have to to cut the
input coming into the cord.
But that's pretty drastic.
But anyhow, pain phenomenal.
We have all kinds of pain.
Have you ever
thought about pain?
Not if you can help it.
You have pain that is
sharp, pain that's dull,
pain that's burning.
All different degrees of pain--
sharp, burning, dull.
And a fascinating
study is referred pain.
When you have something
going on someplace,
like appendicitis,
frequently you
have aches around
your umbilicus.
You think you've got a problem
here with the problems here.
It's referred.
So referred pain.
That's a major one.
I worked on that for
my master's degree
because it was after
the war and the fellows
were coming back
without any limbs.
And yet, their
limbs were hurting,
and there was no limb there.
You had to figure out what
had happened to the nerves
to cause that limb to hurt
when there's nothing there.
So referred pain is a big area.
So now, let's follow pain.
We're going to
need a whole page.
Oh, cultural pain.
I think that's what's fun.
Some people get cut,
and they're so vocal.
They just don't stop
talking about it.
Others will get cut,
and are so stoic.
Oh, I cut myself and go on.
Which are you?
Have to ask your friends?
Right?
No.
I studied this once.
And boy, some great
big massive fellows
couldn't take any pain at all.
And some little tiny with barely
any muscles at all that's in
pain just take it.
He was so stoic.
Just amazing the difference.
Which are you?
You're stoic.
OK.
It's easier on your friends
when you're stoic I guess.
All right.
So what we're going to do is
start at the bottom of a page
because we're
going to bring pain
in but we've got to get it
all the way to the cortex
so we're going to be taking
different slices as it goes up.
All right?
So we'll start with our first
cross section down here,
and then we'll have our
next one coming up here.
And our next one up here.
And since we don't
have much room,
we're going to have
to move over and take
the cortex up here
because that's
our eventual destination.
So this will be a
cross-section of cord.
This will be another
cross-section of cord.
This will be a cross
section through thalamus.
And this will be up to
the central sulcus here.
Do you recall?
Central sulcus or
cerebral hemispheres.
And we're going to
bring in sensation
to the postcentral gyrus.
So our pain and
temperature is coming up
to this part of your cortex.
Post central gyrus.
So we'd like to come in with
these ascending pathways.
There are three neurons
in the pathway--
a primary neuron, secondary
neuron, and a tertiary neuron.
So we're going to
have a primary neuron,
and that's going
to be in your DRG.
What does DRG stand for?
Dorsal root ganglia.
We're not going to
write it anymore.
And the secondary
neuron is going
to be in the posterior horn--
secondary neuron be
in the posterior horn.
Where's the tertiary
neuron going to be?
Where do all
sensations go through
before they go to the cortex?
Thalamus.
Tertiary neurons
in the thalamus.
So when you get
a quiz and you're
asked that you've damaged
your secondary neuron,
you know exactly where
it is, where it's going,
and you could hypothesize
what the result would be.
So we're going to follow
our primary neuron up.
So we need our DRG out here.
And we're coming in then.
Cut your little finger severely
who's got this pseudo unipolar
cell over your
dorsal root, and it's
going to come just to the
lateral aspect of your cord.
Notice I'm not bringing my
posterior horn all the way
to the surface.
It doesn't come all
the way to the surface.
Now, if anybody can figure out
why these have these patterns,
I don't know.
But it's going to
come to an area
out here between
the posterior horn
and the surface of the cord.
Anybody know what
fasciculus that is?
It's named after Mr. Lissauer.
This will be
Lissauer's fasciculus.
I remember taking my class over
for the neurosurgeons once,
and they asked if
they knew the name
and he was so pleased that they
knew Lissauer's fasciculus.
What happens here now, and
this is the question why?
I'm not synapsing here.
I'm just entering and traveling
up to my next segment out here.
Why does it do that?
Why doesn't it come right
into the dorsal horn?
So this axon now will
ascend one or two segments.
Terribly important in
figuring out lesions.
Ascend one to two segments.
And then it will turn and
come into the dorsal horn.
And it's going to come into
an area which is called
the substantia gelatinosa.
This area here.
No.
I want yellow.
And this area is
substantia gelatinosa.
Have you ever
heard of it before?
No?
Why do we have a gelatinous
part of our cord here?
Nobody knows.
Nobody's really
gone in assayed it.
We're driven by technology.
You get new technology, you
leave back all the old things.
Don't bother to go look them up.
Substantia gelatinosa.
So in the substantia
gelatinosa we're
going to have our
secondary neuron.
So we'll pick it up.
And it does something
interesting.
Here is our secondary neuron.
It's going to cross over
to my lateral funiculus
down in this white
commissure down here,
and come over to here.
Don't bring it to the surface
because it's very important it
doesn't come to the surface.
So this is the anterior
white commissure.
Why do I make an issue of it?
Anterior white commissure.
Because there are
certain diseases
where the central canal
boundaries degenerate.
And if they. degenerate,
what are they going to do?
They're going to cut off
your pain and temperature
fibers that are crossing there.
So it's an important
landmark in your cord.
So I'm coming over
to form a track.
This now has to go on
up to our thalamus.
But it's going to ascend over
here in the lateral funiculus
as it goes up to where I'm
going to get into the thalamus.
So it forms a track out here.
All of the fibers
will be P and T--
pain and temperature fibers.
So this tract is called the
spino, where it's beginning,
thalamic tract.
Spino thalamic tract.
And since it's in the
lateral funiculus,
it's the lateral spinothalamic.
When you study this, you'll
find out there are others.
I'm only giving you
the very simplest.
This is lateral
spinothalamic tract.
So if you have to cut
the cord for any reason,
you don't want to cut there.
You'll cut off pain
and temperature.
You've got to know what
else is around there.
And we're going to go
up in our thalamus then.
I'm just going to make
a little block up here
on each side of the
third ventricle.
This is going to be my thalamus.
And these fibers will
come in and synapse,
and I'll have my third neuron.
And it has to go on up coming
up to my postcentral gyrus.
And that's where you'll have
the most refined interpretation
of pain once you get
up to the cortex.
So when we get up
to the cortex--
thank you-- refined
interpretation of pain.
But I'll say one thing because
I want to show a slide of it.
The body is represented
on the postcentral gyrus
in an upside down manner.
So if I have a pain
in my toe, my toe
will be sending
its fibers up here.
My face will be down here.
Why?
What do we call that?
The upside down
representation of man--
homunculus.
I'll show you a picture
of a homunculus.
It's the motor and
sensory we have
to show next time going to motor
down we brought sensory up.
Homunculus sensory
representation of body
on the cortex.
That's again very important
because you can get rid
of your anterior
cerebral artery, which
supplies this area.
What supplies this area?
Middle cerebral.
Right.
Very important for
blockage of arteries
to know the position of these.
Let's see by slides please.
Here we have a cross
section of peripheral nerve.
This is called a scanning
electron microscope.
You can see your blood vessels.
You can see the
individual nerve fibers
that will have the endoneurium.
Then a group will
have the perineurium.
And the whole thing will
have the epineurium.
But this could be
your ulnar nerve.
Look at how
vascularalized it is.
In the next one, this is
just to show the distribution
of the nerves to the surface.
It's a whole field in itself--
dermatomes.
But you see what they're
very clear here for this is
T10, T9, T8, T7 in the thorax.
But when it comes to the
arms, they're different.
You'll have T2 in
here, and you'll
have T1 here because
you have plexi up here,
which are recombining the
nerves as they go to your limbs.
In the next one, and
these are just normal
nerve cells, filled with nissl,
filled with healthy nuclei.
If we cut the axon then
this close it'll die.
But what you'll see
first is swelling,
peripherally displaced nissl,
and eccentric or peripheral
nucleus.
Next one.
And this is the cord with the
fasciculus cuneatus artist
here.
Fasciculus gracilis here.
And we're following here
substantial gelatinosa here.
This would be your Lissauer's
fasciculus out here.
And then we'd have--
whoops I'm sorry.
Can we go back?
I'm sorry.
I could use that same slide.
Back please?
Is it possible?
If not-- no.
Back.
No.
Back.
There.
Thank you.
Now, here is your lateral
spinothalamic tract.
You see it's out here.
But there's a spinal
cerebellar out here.
So you don't want to
have cut through here.
You have to make the decision.
You want to get rid
of cerebellar input
to reduce pain by cutting
a spinothalamic input.
So you need to know, if you're
going into neurosurgery,
the position of all of these.
In the next one.
And then this is our real cord.
We'd have our Lissauer's
fasciculus here.
And then we'd climb
up to the next one,
and come in to your
substantia gelatinosa.
Crossover in the anterior
white commissure,
and come on over into the
lateral spinothalamic tract
and ascend.
In the next one.
Now, these are real
sections of brain.
So we've got thalamus here.
So we're coming up to specific
nuclei with the thalamus
to have our third neuron.
And from there,
we're going to go out
through the internal capsule,
through the corona radiata,
up into our sensory cortex.
In the next one, and
this is showing then
this is our
postcentral gyrus here.
Here's our central sulcus.
So sensory is getting
postcentral gyrus.
And the next one.
Here's our homunculus.
You'll have toes way
up here at the top.
Coming down lots of
hand representation.
The biggest representation
will be hand and face.
But why his face right
side up and the rest
of the body upside down?
Next one.
Oh, this will be
for next lecture
because we've got to
come back down again.
All right.
We'll stop there.
