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PROFESSOR: All right, we have just a little bit at the end
of this class to finish up, and then we'll spend the rest
of the hour reviewing.
We're talking about behavioral state control and these
systems of very widely branching axons.
We know less about chemical diffusion as a means of
controlling brain state, though it's
no doubt very important.
I mentioned the so-called reticular activating system.
I'm not sure if this is really the best illustration because
it's a hindbrain neuron, and usually when we think of the
ascending reticular activating system, we're talking about
midbrain systems.
But these types of neurons are found throughout the reticular
formation of the brain stem, including the midbrain.
Axons with very wide distribution, this is just a
schematic of one in the hindbrain and how it can
activate the neocortex by its projection to the thalamus and
diffuse projection to the thalamus.
Actually, much of that projection goes to what we
call the old thalamus, part of the thalamus that have more
widely branching axons to the cortex.
And then the other system here is in the basal forebrain,
these cells that project to the entire hemisphere.
So those are cholinergic systems, and then we mentioned
the monoamines, serotonin, and the catecholamines,
norepinephrine, and dopamine.
Serotonin, you can see by the color here, distributes
throughout the brain.
It actually distributes much further, it distributes
throughout the spinal cord as well and much
of the brain stem.
Heimer, the anatomist, is picturing its distribution to
the hemisphere here.
Axons that come from these cell groups near the midline
of the midbrain and hindbrain is particularly important in
controlling sleep states.
And that's demonstrated very dramatically by the effects of
lesions in these areas that cause insomnia.
Here's the norepinephrine containing axon system.
It's even more remarkable in the small number of cells that
give rise to the axons.
This locus really is in the hindbrain, only 1,600 neurons,
approximately in the rat, and yet it distributes throughout
the entire nervous system.
Dopamine has less of a distribution, but still a very
important modulator.
It's particularly associated with reward systems.
Remember the ventral tegmental area, and I talked about the
midbrain, the ventral part of the midbrain, when stimulated,
is associated with pleasure and reward?
And it's projecting here to all of the structures that we
call limbic system, structures closely connected to the
hypothalamus, but it also projects into prefrontal areas
of the cortex.
And then the more recently discovered groups.
The earliest ones were in the old thalamus, midline and
intralaminar thalamus that project very widely in the
brain, and then cell groups in the lateral hypothalamus.
Some of these were discovered at Harvard Medical School by
Cliff Saper, the editor of Journal of Compared Neurology,
and he's done a lot of interesting work on these
types of systems.
And the anatomy here has preceded
the functional studies.
We know a lot less about the function of these.
But very interesting things have been discovered, for
example, this system using these peptides, hypocretin, or
oxiraine and dynorphon as transmitters because a
mutation in the gene for those substances or its receptor are
a cause of narcolepsy, a sleep disorder.
Have you all read, or do you know of anyone with
narcolepsy?
Do you know what it is?
What are people with that like?
AUDIENCE: They randomly fall asleep?
PROFESSOR: They fall asleep at odd hours.
A firemen with narcolepsy can fall asleep on the ladder
fighting a fire.
It has some peculiarities in that a person with narcolepsy
can, if he just--
say he's at a dinner party and the talk gets onto some
emotional topic and the person gets very emotional, he can
suddenly go into a sleep state in which his muscles become
paralyzed, which is what happens in dream sleep.
And they'll just suddenly enter that part of dream
sleep, even though in other respects, he's still awake.
So it can be a pretty severe and debilitating disorder.
It can interfere with the ability to work.
All right.
So this discovery was pretty important.
And now that we know the types of neurons it's associated
with, there may be more progress made.
I suppose most of the progress came from the discovery of
animals, certain species of dogs that get narcolepsy.
And it's those animals that they've been able to work out
these correlations.
All right, so we have multiple systems.
I mentioned how you make a few assumptions, you can compute
the number of different brain states that are possible using
different combinations of activity in those systems.
The last question in dealing with the motor system is a
very important one.
The last question I want to raise, namely, why has the
motor cortex become so dominant?
We've talked about projections to the striatum, it's become
the most important input to the striatum, very important
in habit formation.
We know it has direct projections to the spinal
cord, so it can actually bypass the older systems of
motor control, including the midbrain, which were critical
in premammalian animals.
And that was the last topic, talking about the role of the
cortex in controlling the spinal cord.
But it's not only dominant because of its striatal
connections and these direct connections that
bypass other systems.
It has close connections with a system for anticipating and
planning for the future.
A lot of its input comes from these other cortical areas.
In fact, motor cortex gets more transcortical input than
any other cortical area.
It gets cortical input from posterior areas of cortex, the
so-called association areas, and a lot of input from the
prefrontal association cortex.
And we know the prefrontal is concerned with anticipating
and planning, especially the immediate future, what we're
just about to do.
So when we're just about to move our eyes, we say we want
to move our eyes, it's controlled by the prefrontal
cortex that in order to actually move the eyes, it has
to connect to motor areas.
Similarly for speaking, the areas in the prefrontal cortex
where we formulate what we're going to say, but when we
actually say it, it requires the connection
to the motor cortex.
And that's the case controlling the jaws, the
lips, the tongue, and of course, the breathing.
What would you like to do?
You've been given a lot of questions.
You can ask me questions.
I'm happy to answer them.
Another thing I can do is I have gone through the pictures
I've been using and just selected some, and we can just
go through those, because I can point out about a lot of
things that I think are important
that we've gone over.
And that would be one way to conduct the review today.
But if you've come upon any questions that you can't find
answers to, ask me, or ask your teaching assistant,
Andrew Bolton, who's there waiting for your questions.
When I show you these pictures, it's not necessarily
because I want you to memorize any picture.
If we go through these, I can point out the few that you
really should know.
Did you have a question?
AUDIENCE: That was it.
I was just wondering which diagrams we
would have to memorize.
PROFESSOR: You should know this one.
I've shown it what?
Five or six times in the class.
What is it?
It's an embryonic central nervous system of a mammal
showing the hemispheres here.
There's actually olfactory bulbs underneath here that I'm
not showing.
And then the tween brain, so there's forebrain between the
first two lines, and then midbrain, then hindbrain.
I'm showing where the cerebellum develops.
And then of course the spinal cord.
I'm showing a cross section in a developing animal.
In humans, it would look like this early in development.
And this isn't very far from the kinds of cross sections
you see in a small rodent brain, even in the adult.
And I've used that for drawings of pathways too, at
various points in the class.
I do expect you to know a little bit about single
neurons, although it's not been the emphasis.
But we do bring up things about single neurons in
various systems that we talk about.
Some people get a little confused with this because the
CNS is here at the left here, and the CNS is
at the right here.
But it's because I'm placing the receptive end of the
neuron in the same place for the--
the motor neuron here at the bottom, and a primary sensory
neruon innervating the skin there on top.
And I show the axon, and the axon endings, and maybe that's
not very clear either, because this obviously is
not part of the axon.
There are synaptic connections there.
[INAUDIBLE] here just indicating the striated
muscle, but these are synaptic connections.
We call them motor [INAUDIBLE].
And here, there's synaptic connections here.
What are the little enlargements
on the axons called?
AUDIENCE: Boutons.
PROFESSOR: Boutons.
Terminaux in French, the end buttons.
But we always call them boutons.
The French have been dominant for that particular thing.
And then Cajal's work was translated into the French,
and that's where most people read Cajal,
in that French edition.
So that's why some of the French terms
have become so popular.
I didn't copy all these pictures, but I expect you to
know what these types of synapses are.
There were three slides where I just drew them.
We're always picturing axosynaptic and axodendritic
terminals, but you should know that there's axon to axon
contact, usually one ending contacting a
bouton of another axon.
There's also what we call reciprocal synapses, a synapse
with transmission in one direction is right next to one
going the opposite direction, so it's a kind of feedback
arrangement that you find in various places
in the nervous system.
And serial synapses, I picture that also with a process in
the middle.
What that indicates, some of these types of synaptic
arrangements, is that you don't always need an action
potential to get effects at a synapse, just membrane
potential changes are enough to affect the flow of
neurotransmitter in many synapses.
And I didn't copy all these pictures, but I just want to
remind you that we showed some methods, cell stains like the
Nissl stain, fiber stains, like the myelin stain.
I didn't name them here, there's a couple of different
myelin stains.
And then histochemistry, and immunohistochemistry.
Histochemical methods show chemical properties, the
location of particular
molecules or certain chemicals.
It's really the same thing, but we use molecular binding
methods for immunohistochemistry, and
histochemistry, we use laboratory chemistry methods.
So these are the methods.
What do we do with them?
What do we do with these kinds of methods?
What's the main use in neuroanatomy?
Well, we want the regions to look different, right?
We map out different cell groups, different regions of
the brain, different fiber tracks, and give them names.
It's not enough, these methods at the top here aren't enough
to trace a pathway, though.
You could make good guesses.
But to trace pathways using experimental methods, we use
these track tracing methods.
And we talked about the Nato methods, which were the
earliest modern methods, using silver staining for
anterograde degenerating axons.
And then retrograde transport.
I showed pictures of Horseradish Peroxidase, that's
HRP, and color toxin.
And then retrograde transport, that also uses HRP and various
fluorescent molecules.
It can be taken up by a cell and transported
back to the cell body.
And that's what we use to trace pathways in the brain.
So a lot of the things I talk about in the class when I'm
talking about pathways, the reason we know about them is
because of the experiments using these methods,
injections of chemicals usually, and
using transport methods.
Although some of the work done with the Nato stains was so
clear it doesn't have to be repeated, and many of those
studies have not been repeated.
But whenever there was more controversy, they've been
repeated with transport methods.
I used these early studies of George Parker about early
nervous systems that you found in anemones and jellyfishes,
especially the jellyfishes and animals like hydra, that
showed these very simple nervous systems.
The simplest didn't even have interneurons, just an
epithelial cell contacting a contractal cell.
And before that, actually in sponges, you find contractal
cells that themselves respond directly to stimuli.
Then, there's no neuron at all, just the contractal cell
that can respond to input.
So that's the ultimate simplicity in nervous systems.
Combine it all in one cell.
But then you separate the contractal cells, and you have
to stimulate those cells.
You can do it directly, as in these anemones, with an
epithelial cell there that's become specialized to respond
to stimulation and it contacts the contractal cell, and then
you go through a neuron in between.
When that first appeared, you just call it a motor neuron,
because we always call it a motor neuron if it connects to
the contractal cell and stimulates it.
Here, the motor neuron and the sensory neuron is the same
thing on the left.
Here, the motor neuron has become separate, and then you
have interneurons appearing, and its those interneurons
that are between the primary sensory and the motor neurons
that became the dominant cell and nervous system.
There's more interneurons than anything else.
So that's what I use, these concepts, in coming up with
this diagram that's important because of the definitions.
From this, you can define a primary sensory neuron.
It always extends to the surface, or wherever it's
getting its input, although the cell body, as you know,
isn't always out there.
Just the dentritic portion of the cell is out
there in most cases.
And then the neurons they contact are in the central
nervous system.
They're the secondary sensory neurons.
Some of them have long axons, some of them have short axons
to the same region.
And then with varying numbers of interneurons, you finally
reach motor neurons.
And the motor neurons we call the final common path for
eliciting movement, because we can't move
without the motor neurons.
Everything in the rest of the nervous system that's going to
cause any action has to go through those, action here
meaning actual movement of the body.
You could call action awareness, too.
And we know from studying using functional imaging
methods that people that can't move might still be activating
the brain areas concerned with movement control, so they are
still able to think.
So that's a kind of action, too.
But that's a philosophical issue that we're going to
leave for now.
I think it's a very important one, especially in dealing
with patients that have a deficiency in getting input to
their motor neurons.
OK, and the other point here is the motor neurons that
contact striated muscles are shown in the picture, but then
I also show one that has to go through another neuron, a
ganglian cell.
This is what happens in the autonomic nervous system.
So two types of contact there, muscle cells.
Smooth muscle, in the case the autonomic nervous system,
striated, in the case of the somatic system.
OK, and then the evolution pictures.
What was the animal we talked about that was closest to the
very simple undeveloped neural tube?
Amphioxus or branchiostoma.
There are several animals in that group, but there's really
not much study of the details of their nervous system.
They've been hard to study.
They're very small.
And the experimental methods that we use for mammals and
other vertebrate animals have been difficult to apply and
they have not been applied that I know of, though I think
various injection techniques could be successfully applied
to that animal.
And then, with the evolution of head receptors and forward
locomotion, you begin to get specializations at the
anterior end, and so I'm showing an animal here that's
not much beyond amphioxus here, just a few inputs.
I show olfactory, visual, which were the two early ones
for the endbrain, and then I show somatosensory and
vestibular, two early ones for the hindbrain.
And then I show expansions of the hindbrain, because we have
examples of that in living animals.
Remember the fish with the large taste systems or the
large cerebellum?
And then I'm wanting to show here what I call the first
expansion of the far brain, olfactory inputs began to
develop, and they projected right there into the end
brain, which led to some early expansion of the forebrain.
The early olfactory system, from the studies of living
animals, we know went to more than just end brain, it
actually projected into the entire forebrain, and we'll be
talking about that after the midterm.
I'll go over a little bit of that data because of its
importance in talking about brain evolution.
And then in the next class, we talked about things that cause
midbrain to expand the evolution of distance
receptors like vision, that extended now beyond the early
connection to the hypothalamus.
They became imaging eyes, projected to
the midbrain tectum.
They project contralaterally, and I talked later about how
that happened, in my view, anyway.
And I'm mentioning here at this very early stage the main
functions of that connection to the midbrain, both for
escaping, getting away from predators, and for orienting
towards things, mainly food, objects.
And then the second expansion of the forebrain, invasion of
non-olfactory sensory input.
So the first one is olfactory, the second one is
non-olfactory.
Why did they come in there?
Why should they?
They were doing perfectly well with just midbrain context,
hindbrain context.
Why would they extend forward into that olfactory territory?
Why would they do that?
There must have been some advantage, and I think the
advantage was the plastic connections that were forming
in the primitive striatum, allowing habits to form.
And even though that happens to a rudimentary degree in the
spinal cord, hindbrain, midbrain, nothing like what
happens in the striatum.
That required the kinds of connections that
the striatum evolved.
So here I'm showing the tectum developing a connection that
reaches the forebrain by a connection here in the tween
brain, just as an example of how that happened.
So that was stage five.
And then the rest of stage five is expansion of those
hemispheres, and with mammals, it was the appearance of that
dorsal cortex in the more primitive mammals.
Became thicker, expanded.
Very simple genetic changes we think probably underlay--
once they had occurred, the cortex obviously had
advantages for processing of information, and it led to
this incredible expansion.
All you need is a slight change in the genetics
controlling cell proliferation to prolong it, and you can
expand the size of the cortex, either thickness or area.
And the same thing was happening here in the
cerebellum, and those things tended to happen about at the
same time, so I'm showing both of them here.
And what is being pictured here?
Since I was talking about expanding size of brains, I
brought this in here.
Here's the brain increasing in size.
So now I asked, well, how much did it increase
in different animals?
So this is a picture where on this plot, every animal is
just one point here, every animal that was studied, or
they take the mean for the species.
So for example, there were the dot is is human.
And note that the human is furthest from this
diagonal line here.
It's a plot of body weight against brain weight.
The reason for doing it that way is that body weight is
such a major factor in determining brain size.
The bigger the surface area, the more sensory neurons you
need, and the more motor neurons you need to control
the greater muscle mass.
What are other factors affecting brain size?
Anybody?
I don't want you to have the idea that this kind of plot is
the last word on brain size.
What are other factors?
Why among the mammals here is there such a
spread in brain size?
Yes?
AUDIENCE: [INAUDIBLE] specializations like
echolocation?
PROFESSOR: Yeah, specializations led to some
mosaic evolution.
It wasn't only the whole brain that was expanding.
You can get specializations.
Like when the fish developed specialized taste senses, you
got this huge expansion of areas in the hindbrain
processing taste input.
Well, in primates, what's the big expansion there?
What are they so specialized for?
Vision.
Higher vision, tremendous expansion of the visual
cortex, real dominance of the forebrain by the visual system
in the primates.
OK, so that's another factor.
If animals have a lot more sensory acuity in their
fingertips, they're going to have much bigger areas in the
brain representing those fingertips.
Like the rat, tremendous abilities with his whiskers,
so he's got specialized expansions in the end brain,
the Barrel fields of the cortex.
I actually have that picture here.
So that's a factor influencing brain size, though it hasn't
been as an important factor overall as body weight.
And then finally, we would have to add how
smart the animal is.
Cognitive abilities also take brain tissue.
So those are the three factors that I see, but brain weight
is the dominant one, which is why these plots have been done
successfully.
And you can see how different groups fall
at different points.
It's the mammals with their neocortex, that places them
more to the upper left, which means greater relative size.
What's this showing?
It's taken as evidence for evolution from a common
ancestor way way, way back, because when you look very
early in development, the very early embryo, animals as
different as fish and humans look similar.
So at a very early stage, all of the
vertebrates look very similar.
But then as you get later, they start diverging.
And animals that have separated more recently in
evolution remain fairly similar for longer, as you
study older and older embryos.
And that's the sense in which ontogeny
recapitulates phylogeny.
It's not a law by any means, but it's an approximate
relationship.
And then remember I said this was like the brain of a
premammalian animal?
What was the animal group out of which the mammals evolved?
Does anybody remember?
That's OK if you don't.
The cynodonts.
C-Y-N-O-D-O-N-T-S. It was one group of cynodonts.
There's very good fossil evidence that they were
reptile-like mammals, or mammal-like reptiles.
I think the early ones would have to be
called mammal-like reptiles.
We don't even know if they had hair yet, or mammary glands,
but at some point they evolved those.
And I'm sure it took a long time for those things to
appear, so there were transitional animals.
It's not that far from the brain of primitive reptiles,
or amphibian-like animals.
And now they used to say that this was all limbic cortex,
but now we know that in fact, it's more
than just limbic cortex.
There is a cortex that's hard to call limbic, even in
reptiles and even in the frog.
So we just call it dorsal cortex.
It's not neocortex, it doesn't have the six layered structure
of neocortex.
It looks a little more like limbic cortex that's so
coarsely connected to olfaction and to the
hypothalamus.
We say all this, but then I can't tell you too much about
cetacean brains, because in fact, they had this enormous,
expansive cortex, but it doesn't look too much like
neocortex, either.
But in fact, we have not studied it enough to
understand those brains very well.
I hope we can learn more about them without cutting a lot of
them up, because imaging techniques are being used more
and more to study these animals, and I'm doing some of
these studies with a collaborator that I've been
advising for a number of years, that actually got his
start in this class a number of years ago.
All right.
So it's important to know the subdivisions
here, and to know--
you look at this bowl of spaghetti down here and it
doesn't look like anything, but in fact, it's pretty easy
to identify specific things here.
So for example, I show a dorsal root input.
Primary sensory neurons I marked in red there.
I marked in green the secondary sensory neurons, in
the spinal cord or in the cochlear or
vestibular nuclei there.
Here they are for olfactory system.
Here the primary sensory neurons in the surface of the
body, in the nasal epithelium.
And the axon context, secondary sensory cells, and
the olfactory bulb.
We'll be talking about details of that system fairly soon.
And what else can you see here?
Well, look on the output side.
I show the motor neurons going all the way up and down the
ventral part of the spinal cord there in little groups in
the hindbrain, there in groups in the midbrain.
I don't show any [INAUDIBLE] to that, because there aren't
any motor neurons innervating striated muscles rostrum to
the midbrain.
OK, and then I'm showing that some of those motor neurons
contact ganglia, some contact striated muscles, as we
mentioned before.
And then we traced lemniscal pathways.
Those are those long axons going from secondary sensory
cells here up towards the brain.
Those are the rhythms of fibers,
the lemniscal pathways.
I show one going to cerebellum, I show others
going into the brain stem with a few axons making it to the
tween bran here.
One more thing I'll point out here.
I show these secondary sensory cells in the olfactory system
projecting to an area behind the olfactory bulbs, and they
connect directly to the hypothalamus and to parts of
the hemisphere there.
And those same parts of the hemisphere connect to the
hypothalamus.
Those are the limbic system structures.
What's this showing?
Dermatomes.
The dermatome map.
We put the human in the quadruped position just
because then by drawing vertical lines, we have an
approximate dermatome map.
And you see the different levels of the spinal cord
correspond to the different dermatomes because they're
defined, as shown on the right here.
The entire dermatome would be a little wider than shown on
the map here, because there's overlap.
A dermatome is the entire area of skin innervated by axons
coming in through one spinal nerve.
What's a cladogram?
This is one.
It's supposed to say something about evolution.
And what you can see from this is the animals that are living
now are shown at the top here.
There's many animals that they're not showing here,
because their lines ended before you reach-- this is
time going up this way, so this is all now, current time.
These are all living species.
And note that a few of these living species are at the end
of a line that goes all the way back without any branching
to animals that were ancestors of all these other animals.
And that's why amphioxus is so interesting, and why also the
hag fish and lampreys are so interesting,
because they're closer.
It doesn't mean they have evolved since these early
animals, but the fossil record indicates that they've changed
a lot less since this early period.
Because if they changed more, than we wouldn't say it's that
animal anymore.
We'd say it's a different species, right?
And they've just expanded a couple parts of the cladogram
here to show where modern mammals and reptiles and birds
fit, and then some of the seagoing animals up there, the
type is a little small.
And here's when we talked about lemniscal channels, and
there's other pictures there that you can see the details a
little more.
But what I did in this one is to draw in the spinaothalamic
tract on this dorsal view picture, and then I showed
where the axons were in the cross sections, too.
So the synapses are here in the spinal cord, then the
secondary sensory cell axon [INAUDIBLE], and you can see
it in the cross section more easily here.
Crosses over to the other side, and descends with
various branching, the longest ones reach the thalamus, which
then projects up to the cortex.
So that's spinothalamic tract in this top view.
With the top views, you can show the decussations.
So this is class six, and I will post these for you.
Here we were showing, somebody already mentioned this
different size of these midbrain structures, and
animals with different behavioral specializations.
I used pictures like this to illustrate the concept of
diaschisis, eliminating a lot of inputs to cells causing a
depression.
It becomes harder to excite the cells.
Then I'm also showing how it can cause collateral sprouting
to occur, which accounts for a lot of the recovery from
diaschisis.
Here I'm showing the earliest visual inputs coming directly
into the thalamus, but also up here in the pineal eye, we
call it, up into the epithalamus.
And here, I call that [INAUDIBLE], because that's
the neocortex, and I'm just outlining different
subdivisions there, because you should know what all those
correspond to.
If you don't know by now, make sure you ask.
And then I talked about two long pathways, and I had a lot
of different pictures because I dealt with these two types
of pictures separately, pathways
associated with neocortex.
Dorsal column to medial meniscus, going up through the
thalamus to the cortex.
You don't find that pathway in non-mammals, at least not
developed to any appreciable degree.
And then descending pathways cortical spinal, going to both
ventral and dorsal parts of the spinal cord.
And I'm showing those two kinds of pathways then on the
top view too, just because of their decussations there,
right at the junction of hindbrain and spinal cord.
And then we had a couple sessions on development, the
formation of the neural plate, a thickening of the ecoderm,
it's induced by the underlying notochord in all the chordate
animals, forming this invaginates towards the
notochord that forms this group.
It closes off as the neural tube forms just above the
notochord, below the skin.
And then not included when it closed off are what we call
the neural crest cells, and neural crest cells, remember,
become several things.
Primarily, they become the paravertrebral ganglia of the
synthetic system, and the prevertebral ganglia also.
These are the sympathetic ganglia at the thoracic and
upper lumbar levels.
They also migrate to form the melanocytes in the skin, and
they form the adrenal glands.
And I'm defining different parts there
of the neural tube.
We talked about neurogenesis, two kinds of cell division.
The symmetric cell division, the two cells remain mitotic,
and asymmetric cell division, where one of them stops being
mitotic and migrants away.
And this is one kind of migration, migration by
nuclear translocation.
The cells are just very elongated.
This is the peel surface at the top, ventricular
surface down here.
And in this particular cell, the axon starts to form long
before the cell body gets to its final destination.
So here's the cell way down here.
It's moving up the process.
Here you see it moving up, here it reaches the axon, and
only then does it lose these processes.
Now, what would I want you to know about
something like this?
Just a few things.
You should see a lateral horn here, thoracic and upper
lumbar levels.
You can see it here, here, here.
Lateral horn, the preganglionic motor neurons of
the sympathetic nervous system.
Otherwise, we'd just have a dorsal and ventral horn at
every level.
And then you also see the spinal cord is enlarged in the
cervical region and in the lumbar region.
That corresponds to the limbs, because there's more motor
neurons and more secondary sensory cells at those levels,
especially motor neurons.
And then you see in the gray matter how anatomists have
divided it into layers, with the groups of motor neurons
here in the ventral horn, What kind of stain is this?
What kind of stain is that?
Well, it's staining something black around the side there.
And we already know this is cells in there, so that must
be fibers, the axons.
It's a myelin stain, staining the myelinated axons.
So even though we can't see the cell stain with that, we
can see where the cells are, because it leaves it less--
it's much less stained.
So it's a useful stain in
subdividing the nervous system.
This shows a cross section of the top of the spinal cord, at
the top the very top of the cord where you have the dorsal
column nuclei, and I'm just showing there that the lower
body is represented in the most medial one, then the
upper body, and then finally, in just that upper part of the
cord, you have axons from the face are terminating.
That's when you first have a homunculus, that's the lowest
part of the nervous system where you have an entire
representation of the body's surface, from the most caudal
to the most rostral part of the body.
And here, I'm showing proprius spinal fibers on the left,
cells that begin and end in the cord.
They always travel very close to the gray
matter in these columns.
And then I'm showing where the cortical spinal axons are
found in primates, and the rubrospinal axons.
And then I show where these various systems that I show in
green here controlling axial muscles are found.
They're all found in this ventral region.
All right, I will post the rest of these online, so
you'll have some idea.
This one, I again would not expect you to memorize at all.
I just want you to understand about the meninges and the
role of the astrocytes there separating the
neurons from the blood.
And a little bit autonomic system.
For that, if you simply know how the gut, or the heart, of
the iris of the eye is innervated by both systems,
you should be able to say a little bit about that, the
nature of the innervation and how it's
different in the two systems.
OK, so I'll post these.
And if you have questions, I will be reading the next few
days, the forum carefully, so if you want to put a question
up there, fine.
I'll answer it or Andrew will answer it, just to help you
get ready for this.