PROFESSOR: Now, let's go back
and look at our spinal cord.
I gave you two pathways that
were essentially ascending,
just to review them for you.
Let's take this.
If you recall, we filled
up the posterior funiculus.
This was our posterior funiculus
with just one modality.
It was kinesthetic sense.
This is our poster funiculus.
Just reviewing for
a moment before we
bring in the descending.
These are ascending paths.
Get you focused on the brain
all of a sudden from out here--
bring it in.
And we said we had a fasciculus
gracilis, just repeating,
and cuneatus, and that
these were ascending paths.
They're carrying
proprioception--
proprioception, also referred
to as kinesthetic sense.
And then we gave
you the pathway.
This one I should mention to you
because it's an important one,
since it takes the
whole posterior
funiculus for just one
type of sensory modality.
It will have a
dorsal root ganglia.
Number one will be the DRG.
Number two will be different.
It will be the medulla, and I
just think you should know it.
Because when you cross
the bay, you'll get it.
So, it'll be the
medulla for this path.
And number three will be what?
Thalamus, sure.
They've all got to
go to the thalamus
before they go to the cortex--
all right.
And, then, we gave the
lateral funiculus--
because, see, both of these
here will be filled up with--
These are both right and
left posterior funiculus.
So, we essentially filled almost
a third of our white matter.
Then, we put in here a
lateral spinothalamic tract.
We just did it one
side, but I want
you to get the vision
these are on both sides.
So this was our lateral
spinothalamic tract.
And what was it carrying?
Paying attention--
good for you, right--
terribly important.
Pain and temp.
And we had our three
neurons for it,
and the first one was where?
The first one's always the same.
Where's the first one?
Nobody want to say?
The DRG, sure.
And then the second
one was where?
STUDENT: [INAUDIBLE]?
PROFESSOR: Pardon?
STUDENT: [INAUDIBLE]?
PROFESSOR: No.
That was the second one for the
proprioception in the posterior
funiculus.
This one-- It's an exception.
Where is it?
STUDENT: Substantia gelatinosa.
[INAUDIBLE]
PROFESSOR: That's correct.
And where is the
substantia gelatinosa?
STUDENT: In the dorsal horn.
PROFESSOR: Terrific.
Good for you.
I gave them dorsal horn and,
specifically, substantia.
No, my students here
take this all casually.
And then I see them on campus
once they are over there.
And they said, my gosh.
Everything you said, we're
getting over here too.
And they use it, and so it
is important-- substantia
gelatinosa.
And the third one was where?
STUDENT: Thalamus.
PROFESSOR: Yeah, thalamus--
just begin to reason with it--
begin to use it.
You will when you
start having problems,
then you'll remember all this.
So now we will take all
of these from the thalamus
to the cortex.
And do you remember
the sensory ones, where
they were going on the cortex?
Postcentral gyrus, right.
And this was our
postcentral gyrus--
postcentral gyrus.
Good for you.
So we've got sensory
up to the cortex.
Now, we want to have a response.
We've got to take
motor back down again.
So let's start with
our descending path.
And these will be motor,
and we'll have two of them.
We'll have-- first one
is called corticobulbar--
corticobulbar.
And what does that mean?
You'll find with these paths
that the first word in a path
tells you where it begins.
So this is going to begin
in the cerebral cortex,
and you'll say, what in
the world is the bulbar?
They used to call the brain
stem the bulb, and that's why.
These tracts are going from
the cortex to the brain stem,
in the modern derivation
of brain stem.
This will include the
midbrain and the hindbrain,
the parts that are in the
main stem, not the cerebellum.
And so corticobulbar tracts--
and an example
would be, since it's
going to cranial
nerve nuclei, it
goes to cranial nerve nuclei.
And let's just take the
fifth cranial nerve nucleus.
Now, who can remember
what's the motor component
of the fifth cranial nerve?
Nobody?
Did you chew your
breakfast this morning?
Did you think what would
happen if you didn't
have this nerve in intact?
STUDENT: Muscles of mastication.
PROFESSOR: Muscles of
mastication, sure--
muscles of mastication.
So this will be
coming from the cortex
down to the nucleus of the fifth
for muscles of mastication.
Then the other tract will
be the corticospinal tract.
So, from its name,
it's obvious it's
going to go from the
cortex to the spinal cord.
And that's the major one
for the rest of your body.
So we're going to follow it.
We were just introducing
corticobulbar.
These two run together some
of the time, not always,
but they leave the
cortex together.
One and two leave
cortex together.
So where are they leaving?
What part of the cortex
are they coming from?
We took sensory to
postcentral gyrus.
We're going to take motor
from precentral gyrus.
Sometimes these work and
sometimes they don't.
So we're going to follow
the corticospinal tract.
And it's going to originate
in the precentral gyrus.
So here is our central sulcus.
And we're going to have a
gyrus just in front of it,
and that's our precentral gyrus.
Can you picture
yours in your brain?
I mean, you felt all over for
your bones and your muscles.
How much have you transferred
this to your brain?
I mean, you can sort of see
you're going to central here.
Precentral would be in front
of it, postcentral behind.
All right-- so now,
let's follow this.
We've got to get down
to the spinal cord.
So we've got a lot of
brain to go through.
I'm just going to
take off this one
and use this drawing
to show how we're going
to take sections coming off.
So, we're going to sort
of expose our midbrain
a little bit more
than it's exposed,
and then we come down--
come to our hindbrain.
We've got our
cerebellum out here,
and then our medulla coming
here, and our foramen magnum
and our cord.
So we want to get
started with a section
through our precentral gyrus.
We'll take a coronal
section through.
So A will be what we do.
We need a whole page.
So begin at the top of
a page, because we're
going to be taking this
down through the segments.
Put some gyri here.
And we'll put in
the basal ganglia,
as we've seen it, as
a representative here.
So this will be our
precentral gyrus.
These will be our representative
of the basal ganglia
for landmarks.
Do you remember what
basal ganglia did for you?
Modifies your motor behavior--
keep it smooth and coordinated.
And then, let's start now
with our pyramidal cell
up in the precentral gyrus.
It's going to be the origin
of our corticospinal tract.
We have lots of
pyramidal cells up here.
And their axons, then,
are going to descend.
They have to go through
the internal capsule
so they confine in the apex
area of the basal ganglia.
And what have we
developed here--
all of these axons in here.
I'm just going to put Xs here.
What do we call the mass of
white matter between the cells
up here and the cells
down in the basal ganglia?
Corona radiata.
It's white matter.
And it's often
affected with disease,
so they talk about
the white matter
of the cerebral hemispheres--
the corona radiata.
So, where I put--
See, it's only white
matter between these cells
and these cells, so this equals
the corona, the radiating
crown, radiata.
Clinically, it's used a lot.
And then we come down
to the area here.
This will represent part
of the internal capsule,
as these fibers
are condensed here.
Fibers going to
and from the cortex
are all condensed in here.
I'm only giving you
one set of fibers.
So in red, I've put
internal capsule
for corticospinal tract.
Because, you'll
learn, eventually,
the blood supply of this whole
area-- very important, you see.
Break a blood vessel here,
and you're paralyzed.
These are your main
fibers going down.
So let's now take the
midbrain section--
Where?
Are these fibers going
through the midbrain?
So we put our colliculi--
lets you know we're at
collicular level, midbrain.
What's the name of our
former central canal here?
Aqueduct, good--
just repeat, repeat.
And down here, on
the ventral surface,
these are motor fibers.
So you're going to see I'm
on ventral, not dorsal.
This was sensory up here.
This was visual,
auditory sensory.
This is motor.
We'll see our paths coming
through here, down here
in our cerebral peduncles.
But, in the middle,
there are lots
of other fibers going down.
I just have to do it this
way because I don't have
the dimensions, but you realize
this is a continuation down,
and we pick them up here
in the cerebral peduncles.
These are cerebral peduncles.
And our next area will
give the upper medulla.
This was midbrain, so you
learn the characteristics
of each part of the brain stem.
That's the beauty of it--
no two parts are the same--
a real challenge.
So my next drawing will
be of the upper medulla.
Who can tell me what the
ventricle will be here
over the medulla?
Four, sure-- fourth ventricle.
And will my motor
pathway in the medulla
be up here or down here--
up or down?
Which is dorsal and
which is ventral?
This is dorsal.
This is ventral.
Will motor be dorsal or ventral?
STUDENT: Ventral.
PROFESSOR: Thank you.
My, that is so fundamental in
learning about your brain--
when you've got bleeds
to know the difference.
So we have what
are called then--
they take a
pyramidal shape here.
These are still the same fibers.
But at the medulla level,
they look like this.
So, if you saw something that
looked like that, what would
you call it?
STUDENT: Pyramid.
PROFESSOR: A pyramid-- yes.
These are pyramids.
So down here, they call
it the pyramidal tract,
if you want to.
But it's still the
corticospinal tract,
but just going
through the medulla.
All right, what
happens to it next?
This was upper medulla.
By the time we get
to lower medulla,
it does something different.
So we've got-- oops,
don't want that one.
Lower medulla looks
something like this.
This is lower medulla.
[BEEP]
Whoops, can you
check that, please?
Thank you.
What's happening in
the lower medulla
to this corticospinal tract?
It's deciding to cross.
You think we understand
anything about this brain?
Why in the world is it going
to wait till it gets down here
and then cross?
So we have what's called the
decussation of the pyramids.
So it comes from the
pyramids, and they cross.
So this represents the crossing,
or decussation of the pyramids.
But only 80% to
90% of them cross.
What do the others do?
They continue to
stay where they are,
and I'll mark them in
a different color here.
Those in the medial area,
here, will stay here.
In green, these are uncrossed.
So now, our next section--
because what we've
taken here, we've
taken one, here, in midbrain.
This was A. Then, A
was up here, up here.
Then B will be midbrain.
We've taken it through here.
And C-- this is B, and this is
C down here-- upper medulla--
would be upper medulla.
And then D is lower medulla.
So we get them
from all directions
so you become
familiar with them.
So our next one will be
E, will be spinal cord.
We've reached our destination.
E will be spinal cord.
And it's become an old friend
now-- you're familiar with it--
posterior horn, anterior horn.
You know we're not
in the thoracic cord.
How do you know that we're
not in thoracic cord?
STUDENT: Lateral horn.
PROFESSOR: The
lateral horn, right.
We didn't have time to
give you a lateral horn.
But if this were
a thoracic cord,
you have very thin horns because
you don't have much muscle
mass around your thorax.
But you also have a lateral
horn, so it differs.
It has thin horns
and a lateral horn.
I'll just slip this
in at the moment.
And why do we have a thoracic
cord that has lateral horns?
Because this is the connection
of the CNS with the ANS.
This is for the ANS.
When we get to the
ANS, we'll get to that.
But I just wanted you to see, if
you see one of these like this,
you know you're not in thoracic.
But we've now crossed, and
we've brought these fibers up
to this position.
So who's going to tell me in
which funiculus in the cord
will this group
of fibers descend?
In the posterior, in the
lateral, or in the anterior?
STUDENT: [INAUDIBLE]
PROFESSOR: Pardon?
STUDENT: Anterior [INAUDIBLE].
PROFESSOR: Anterior--
only the uncrossed.
See, they're here-- they're
going to stay there.
But look at what I drew here.
They're up here--
Where are they going
to be over there?
STUDENT: Lateral.
PROFESSOR: Lateral--
good for you--
right.
So, we're going to
have them coming down
here in the lateral funiculus.
So this is still our
corticospinal tract.
But we could add a definition
to it, where it is, a location.
So we'll call it the
lateral corticospinal tract.
And this one becomes the
medial corticospinal tract,
or anterior.
So now it's time,
because our destination
is the anterior horn cell.
Where are we going to find
the anterior horn cell--
here or here--
one or two?
STUDENT: Two.
PROFESSOR: Two, sure.
Those are your anterior horns,
so there you'll find it.
Let's make an anterior
horn cell so we
can bring in this cortical
control, multipolar cell here,
with its axon going out
over the ventral root.
So now we'll have
fibers that will
leave our lateral
corticospinal tract
and come over and synapse
with our anterior horn.
We'll call this 1.
1 will be synapse directly
with anterior horn.
So is this going to be for
refined movement or crude
movement?
What would you guess?
STUDENT: Fine.
PROFESSOR: Fine,
right-- fine movement.
It comes directly to
the anterior horn cell.
So this is for fine movement.
For more generalized
movement, my fibers going to
come over to an interneuron--
we talked about interneurons--
and then down to your
anterior horn cell.
So, for general movement,
not this fine movement,
we come into an interneuron and
then to the anterior horn cell.
And we did this one in blue.
Now, you say, well, what
about this other 10% to 20%
that hasn't crossed
yet that's down here
in our anterior
corticospinal tract?
Well, those fibers--
these will cross
at this segment in
the cord where they're
going to leave the cord.
These will cross
in segment of cord
where exit cord, let's put.
So they will eventually,
further down--
I'm not going to draw a
full picture for them--
they'll come in and cross.
But that's a fascinating
system in itself.
Why in the world is
it doing all this?
All right, now we want
to talk about what
are known as upper motor
neurons and lower motor neurons.
Because when they're
damaged, they put about--
bring about completely
different symptoms.
So our upper motor neuron
will be our pyramidal cell.
That's an upper motor
neuron, because we've
seen we have two
neurons in this tract.
Its axon will come down
to an anterior horn cell,
where we'll have the lower.
This is anterior horn cell.
These are lower motor neuron.
And, as neurologists, they
have to know the difference
in what happens if I cut here--
have an automobile accident--
my cord gets cut as it's in its
lateral corticospinal tract.
And what are going to be
the symptoms versus a cut
that I get down--
that impinges on my
anterior horn cell?
So this is called an
upper motor neuron lesion.
And we'll see various
clinical symptoms.
The first is called
flaccid paralysis--
flaccid paralysis.
And what is that?
That's a very weak, or feeble,
paralysis, not a strong one.
It's a weak, feeble paralysis.
Shortly after the
injury, it will change.
That's one characteristic--
It'll change to a
spastic paralysis--
a spastic paralysis.
And the spastic paralysis
will be a continuous contained
paralysis, but it's
not a strong one--
but it's a continuous one--
continuous paralysis.
The next one is that the loss
of superficial reflexes--
loss of superficial--
superficial reflexes.
In the male, that'll be the
loss of a cremasteric reflex.
You know where your
cremasteric muscle is?
It's the muscle that's
attached to your testis.
And when it gets
too cold, the testis
moves up toward the abdomen when
the cremasteric muscle pulls it
up.
So the cremasteric--
cremasteric reflex--
is a superficial one.
You just stroke this muscle,
and the testis will ascend.
In other words, it
comes out of the cold.
So that's a superficial reflex.
Four, you have an exaggeration
of deep tendon reflexes--
exaggeration of deep
tendon reflexes.
And obviously, these
are easier to test.
If you just tap your
patellar tendon--
and if you have an upper
motor neuron lesion, instead
of just giving a short--
it flies up.
So, if you're testing
for it, stand aside
because you get
kicked in the chin
if he really has an upper
motor neuron lesion.
But I saw one over at UCSF,
and the neurologist-- this
was when I was a student,
and we were visiting.
And they said, well, would
you like to see an upper motor
neuron lesion?
Sure.
And so he tapped, and her
knee didn't do anything.
Tapped.
And he was so
embarrassed because this
was supposed to demonstrate.
Turned out she had
on woolen underwear
that was that thick under
her slacks, that wasn't even
getting through to her tendon.
So, to let you know, as young
physicians, be sure you're
tapping the tendon and
not all the underwear.
All right-- exaggeration.
Deep tendon reflexes--
that'll be the knee jerk.
And the last one is
a positive Babinski.
A positive Babinski.
Whoops-- whoops--
trying to hurry here.
We've got so much to cover,
and we're not making it.
OK-- positive Babinski.
And what is this?
You stroke the sole of the foot.
Your toes are usually like this.
If you have an upper
motor neuron lesion,
the toes will fan out.
So, stroke sole of foot.
But you have to stroke it
with something, not just
with your hand.
When we saw this same
doctor, he used his keys--
just took a key and struck
and the toes went out.
So you have to really
get the impulse through.
Stroke sole of foot and
the toes will fan out.
So that's a positive Babinski.
So the sure ones
that are easy to test
would be the positive Babinski
and the exaggerated deep tendon
reflexes.
That'll let you know that
you're on the right track
for an upper motor
neuron lesion,
because the lower
motor neuron lesions
are fairly obvious and
easy for you to figure out.
A lower motor neuron lesion--
this is going to be damage
to our anterior horn cell.
Where is it going?
Skeletal muscle, right?
Remember your skeletal muscle
with peripheral nuclei?
So it's going to muscle,
and we've cut it.
So what will we see?
Loss of reflexes-- we have
no function from the muscle.
Loss of reflexes.
With time, the
muscle will atrophy.
You need your nerve
connection to your muscles
for them to stay healthy.
You cut them, muscle dies--
atrophy of muscle--
and what happens?
You get paralysis.
So what used to be the
well-known disease that
attacks these?
Polio, the polio virus--
the virus of poliomyelitis.
And you see the people
without the muscles in a leg
if it attacks just the
lumbosacral anterior horn
cells.
But it gives you
an idea of why it's
important to know your pathways.
There are connections
with the nerves
and the symptoms
related to them.
So, with that, we'll move on
to the cerebral hemispheres.
And, as we said, the
cerebral hemispheres
account for about
85% of your brain.
I mean, they're that
big, massive amount.
And the cerebral cortex will
be the few layers of cells
that cover these hemispheres.
What does cortex mean?
It means bark, so these
are the outer layers
of cells on the hemispheres.
There are only-- and
your occipital cortex
is only a millimeter thick.
It's very thin.
It's thickest-- frontal
cortex is thick--
thicker.
It gets up to 4 millimeters
occipital, down to 1.
So we've talked about the
cortex because we've talked
about the bones on the outside.
So we know what our lobes are.
We've had them, but we didn't
get them in much detail.
We'll see how much
detail we can give you.
Because some of you will
want to go into embryology
and find out how these nerve
cells migrate to where they
are, how they know how to
get there, how they know what
transmitter to give.
I mean, all the decisions
that these cells have.
Do you feel tired just
thinking about them?
I mean, all that time I
was using all those cells
for my motor activities, right--
for talking, that had
to be synchronized--
with hand movement,
which was corticospinal
versus cortical bulbar.
It's just so phenomenal.
So now, our cerebral
hemispheres-- we're
going to take the frontal lobe.
The frontal lobe is the
largest behind your forehead.
And we've already
had parts of it,
but I want to give
other terminology which
is used clinically.
So we've had our
precentral gyrus, right?
So this is our precentral gyrus.
And now we're going to introduce
Brodmann's terminology,
because this is used frequently.
Brodmann-- lots of people have
given numbers to the cortex
so that you can talk about
area two, three, four,
but Brodmann's has been
one that has stayed.
So he has the numerical
designation of cerebral cortex.
So precentral gyrus is
going to be area four.
We talked about area four--
you know exactly where you are.
We said the precentral
gyrus gave rise
to the corticospinal
tracts, but other areas that
were going to develop--
participate-- we'll
mention those as well.
Let's go first-- this is our
refined motor for precentral.
Then we go to premotor.
Premotor is six.
So it's for more generalized
moves, less specific motor.
Where I like it is
on the medial aspect.
What is six doing on
the medial aspect?
It's still-- it's called
supplementary motor
on the medial aspect of the
hemisphere, where we have
our corpus callosum in here.
We have our central sulcus here.
Then, this would be area
six on the medial aspect
for behind it.
This is supplementary motor.
What's it doing for you?
It's visually planning
your motor activity
before you ever execute.
How many of you are divers?
How many have ever been
off 3-meter boards?
Yeah.
We were always on those as kids.
That's what you do growing
up in Southern California.
You did your flips,
you did all of this.
But before you left
the end of that board,
you planned what you
were going to do.
Watch the Olympic divers.
They stand there
before they ever go off
and twist and everything.
That's premotor
supplementary planning.
Isn't it wonderful--
I mean, you do it when you're
on the basketball court.
I mean, you're deciding
how much-- oops--
you've got-- I'm on
the basketball court
when I was supposed
to be finished.
This is supplementary motor
for planning motor activity--
fascinating area.
I'm going to give you one more.
I'm going to give
you area eight.
These are for
frontal eye fields.
Because we know vision is all
the way back in the occipital,
but here we are in the frontal.
These are for conjugate
eye movements.
We've talked about those before.
So we're seeing a lot of
this frontal lobe is motor,
but this is both eyes
working together.
So let's look at our slides,
and we'll finish this next time.
All right.
Here's our cortex as we
see it from the side.
We'll have our central sulcus--
we'll be coming down
here-- your central sulcus,
postcentral gyrus,
precentral gyrus.
And then we just gave the
premotor area and then
the frontal eye fields here.
And the next one--
and this shows that
you'll have a--
we said a sensory homunculus
on your postcentral gyrus.
Well, you have a
motor homunculus
on your precentral gyrus.
Again, I asked you why
is this right side up
and the rest of the
body is upside down?
Nobody gave me an answer yet.
And the next one.
And this is showing
that corona radiata.
Here's my cortex out here,
on the gyri and sulci.
The axons have to get all
the way down to either--
as corticobulbars-- to cranial
nerve nuclei and the brain
stem or corticospinal
anterior horn cells.
And the next one.
And this shows, again,
here, your basal ganglia.
I'm sorry, this is
an unstained brain,
so you can see how dark they
are just because of pigmentation
and blood vessels.
Here was your caudate.
Here was your putamen
and your globus pallidus.
The fibers are coming from here.
They're coming down by the
genu of the corpus callosum
here and going on
to the next one.
Next one please.
And down here were our cerebral
peduncles, colliculi, aqueduct,
substantia nigra, all midbrain,
but this part of our peduncles
will be our corticospinal
tracts traveling down.
You break a blood vessel
here, you'll get paralyzed.
Next one.
Now we're down at upper
medulla, and you'll
learn some day what the
characteristics are.
This nucleus here will tell
you it's upper medulla,
but here are your pyramids--
pure tracts coming down.
Next one.
And now they're crossing,
and it gets sort of messy
when they cross.
It's not as pretty a
picture as it usually is.
Anybody tell me what group
of cells these would be?
Do you remember
the tract gracilis?
These would be the
nuclei for the gracilis--
just to see if you
could figure things out.
Here we go-- so,
we're going to cross--
Let's see the next one.
It'll be less crossing.
It's hard to get
one that does it
just like we do
on the blackboard,
but all this mess is crossing.
And the next one.
And here we are
down on the cord,
so we're going to be out
here in the lateral funiculus
with our lateral
corticospinal tract
and our anterior corticospinal
tract in the anterior
funiculus-- here where
our posterior tracks
in the posterior funiculi.
And the next one.
And we didn't get as
far as we wanted to,
so I can't go on with the
rest of the gyri on this.
Let's see one more.
Do I have one more,
or was that it?
Yes, it will be visual cortex.
We'll get it next time.
But here's your
supplementary motor cortex
up here for planning
your activity, all right?
