- [Instructor] So this laboratory will cover an overview
of the nervous system,
both the central nervous system
and peripheral nervous system.
Before we begin looking at the brains,
I want to take a few seconds to talk to you about
how we have this wonderful opportunity
for you to see the brains.
And this is due to the fact
that local Vermonters have given selflessly of themselves,
not only them, but their family members,
to make the decision to donate their body
to the Department of Neurological Science's
Anatomical Donor Program.
They gave their brains with the intent of teaching others.
So we want to use respect when we examine these specimens.
So the first specimen we're going to look at shows you
an example of how the brain sits within your body.
This is a sagittal cut,
a midsagittal cut right down the brain.
You can see the skull is here.
We have a thin membrane
called the dural septa.
Specifically, this dural septa is called the falx cerebri.
It separates the two hemispheres,
cerebri coming from cerebrum.
And what this membrane does is prevents your brain
from moving side to side or laterally.
There's another membrane that you can't see here,
but we'll see in another specimen
called the tentorium cerebellum,
cerebellum because this is the cerebellum.
This membrane actually continues down horizontally here,
and what it does is prevents the brain
from moving around too much up and down.
The central nervous system consists of the brain
and spinal cord.
The five components of the brain are
the cerebrum,
the diencephalon,
the brain stem,
cerebellum,
and spinal cord.
So one of the things I want to impress upon you is
how small the spinal cord is.
And this is the largest part of the spinal cord,
from here to here.
We'll see it in another specimen.
This enlargement is called the cervical enlargement.
The cervical enlargement is large
because this will contain the spinal nerves
that are going out to innervate your upper extremity.
And when we look at the spinal cord,
we will talk about the dorsal
and the ventral components of the spinal cord.
The dorsal spinal cord is on the back of the body.
The ventral spinal cord is underneath,
ventral, close to the viscera,
close to the guts here.
So what we're seeing here are the dorsal roots
of the spinal nerves that are coming in,
bringing sensory information into the spinal cord.
Now, what you can't see down here is another enlargement
in the lumbar region,
and this is going to go to innervate the muscles
of your lower extremities.
Now, your spinal cord actually ends
in the lumbar vertebrae.
So what you have to appreciate
is that the spinal cord
at the end is essentially nothing more
than a bunch of really long nerve roots.
And this looks like a horse's tail,
and that's why this area of the spinal cord
below the ending is called the cauda equina.
We'll see this in a closeup shot in another specimen.
So this is another sagittal cut of the brain.
And I think what I want to have you appreciate,
how little space there is between the brain
and this membrane
called the dura membrane.
There are three meninges that cover the brain,
the relatively thick dura mater,
right underneath it the arachnoid matter.
There is space underneath the arachnoid mater
called the subarachnoid space.
This space is filled with cerebrospinal fluid.
So the brain actually floats
within cerebrospinal fluid.
And that's why, again,
we need these two membranes, called dural septa,
to help separate the brain.
This, as we saw in the previous specimen,
is called the falx cerebri.
One dural septa that you couldn't see on the last specimen
was this membrane right here, the tentorium cerebellum.
This is the cerebellum.
So the five parts of the brain,
again, are the cerebrum,
the diencephalon,
the brain stem,
the cerebellum,
and what you can't appreciate here is the spinal cord.
Now we're looking at the nervous system
from a different perspective,
outside of the body.
This dissection represents a Herculean effort
by Bruce Fonda, an anatomist here in the department,
who painstakingly not only took the brain out of the skull
and the spinal cord out of individual vertebrae
but actually followed out the major nerves
of the arm and the leg.
So again, I want to focus on the concept
of dorsal and ventral.
Since this person is laying on their back,
the side of the spinal cord that we're seeing here
is the ventral spinal cord.
So this would contain the ventral roots
or the motor neurons that are going out to muscles
to cause muscle contraction.
The nervous system contains the cerebrum,
the diencephalon in this case we can't see,
the diencephalon you have to see from inside,
the brain stem,
the cerebellum,
and the spinal cord.
Now, one of the things that you hopefully can appreciate
here on the brain stem
is that this is the vascular tree
that's going to provide the blood supply
to the brain stem and the brain.
Another thing I want you to appreciate from the ventral
or underside of the brain are these nerves.
These nerves are called cranial nerves.
The cranial nerves are similar
to the spinal nerves.
Cranial nerves contain sensory,
motor, and autonomic innervation,
but this information is only going to the head and neck.
Spinal nerves, like the cranial nerves,
are receiving sensory information from the body,
sending motor information to the body,
and in two regions of the spinal cord,
in the thoracic region
and in the sacral region,
it also has what we call autonomic innervation.
Autonomic innervation for the thorax
is going to the viscera,
the heart, the lungs, the GI tract.
In the sacral region of the spinal cord,
the autonomic innervation is largely going
to the bladder, bowel, and your reproductive structures.
Now, and if you zoom in carefully here,
you can see that there are some spinal nerves
that come straight out as individual units.
However, in several regions
of the spinal cord,
individual nerves join together with other nerves
to form the superhighway
that are called plexus,
plexuses or plexi plurally.
So what this is
is the accumulation of individual nerves,
and we have three major plexi.
Technically, there are four.
You have the cervical plexus,
the brachial plexus,
the lumbar plexus,
and the sacral plexus.
And quite often the lumbar
and sacral plexus are merged together
into the lumbosacral plexus.
And the biggest nerve of the lumbosacral plexus
is the sciatic nerve.
This is what gives you, if you sit on your wallet,
this is what gives you the pain sensation
radiating down your leg.
Now what we're going to do is go
and look at the anatomy in greater detail
of the brain and the spinal cord.
So we'll start working our way up the nervous system,
starting with the spinal cord.
This is where we'll bring in sensory information.
When you look at the spinal cord,
you could see, just like the brain,
the spinal cord is surrounded by dura mater,
arachnoid mater,
a subarachnoid space that's filled with cerebrospinal fluid,
and then the third meninge that we can't see,
either here in the spinal cord or in the cerebrum,
is the pia mater.
And the Pia mater is just a single cell layer thick
that surrounds the brain.
Now, you really can't tell from orientation here
without it being in the body
which is dorsal sensory
and which is ventral motor.
The one thing that you can appreciate here
is these little balls
that are sitting adjacent to the spinal cord.
These balls are actually the collection
of nerve cell bodies of sensory neurons.
These are called the dorsal root ganglia.
There are no synapses
in the dorsal root ganglia.
The dorsal root ganglia only represents
the cell body, the soma, or perikaryon,
three terminology that you should be able
to use interchangeably
that represent the sensory neurons
entering into the spinal cord.
In order for you to see which is dorsal
and which is ventral,
what you'd have to do is you'd have to look
at a cross section of the spinal cord.
So here we have a cross section of the spinal cord,
and you can tell which is dorsal
and which is ventral
by the shape of the gray matter.
The spinal cord has a central gray matter
surrounded by white matter.
The white matter represents the axons
of sensory neurons going up
to the cerebrum
and the axons of motor neurons
from the cerebrum coming down.
This is the dorsal side of the spinal cord.
This is called the dorsal root entry zone,
and you can see it's contiguous with the outside.
Generally, the ventral root doesn't go all the way down.
There's a little bit of white matter that sits around here.
So the dorsal root is going to have sensory information
and the ventral horn here.
So this is the dorsal
horn of the gray matter
and the ventral horn of the gray matter.
This is where the sensory neurons
that came in through
the dorsal root of the spinal nerve
are going to synapse.
They'll then have motor neurons
that will then exit the ventral root.
When the dorsal root of the spinal nerve
and the ventral root of the spinal nerve come together,
you have what's called the spinal nerve.
And again, in certain areas of the spinal cord,
in the thoracic region and in the sacral region,
in addition to having sensory afferents
and motor efferents,
you will also have autonomic nerves
that are going to innervate the viscera.
Now, one of the things that you might not have appreciated
is when you look at how the spinal cord sits
within the vertebral column
and how the spinal nerves exit,
you can see that the spinal nerves exit
through a relatively small space.
So if you have a crush here
that damages or compresses the spinal root,
you're going to take out
not only the sensory information coming in
but the motor information coming out.
Finally, if we look here at the very end of the spinal cord,
something that we also couldn't appreciate
in the other two specimens that we looked at
was that the spinal cord ends
in a rather tapered structure called the conus medullaris
and that all the nerves that are coming out
after that are called the cauda equina.
But the other thing that I want
to point out is this structure right here.
This is a connective tissue structure
called the filum terminale.
It is the terminal end of the spinal cord,
and it's a piece of connective tissue that attaches
to the dura.
And just like you had dural septa
that helped support the brain
and prevent it from moving inside of the skull,
the purpose of this filum terminale
is to attach the spinal cord to the dura.
Because it likewise is floating in cerebrospinal fluid,
and you don't want it to be jostled around too much.
Now what we'll do is we'll move up
and focus exclusively on the brain.
So we saw how the brain fits inside of the skull.
And now that we've seen the brain outside of the skull,
you can see how really thin that dural membrane is.
Remember, underneath the dura is going
to be another layer called the arachnoid matter.
And underneath the arachnoid matter,
we're going to see our superficial blood vessels.
So when the specimen,
looked at the specimen that was lying on its back,
we saw that there are blood vessels that run
underneath the brain,
primarily around the brain stem.
But you can also see that there are lots
of blood vessels here throughout the entire brain.
And we'll have another lab devoted
exclusively to blood supply.
So unlike the body that has
what's called the lymphatic system,
you know that you're sick
when your lymph nodes swell.
All right.
Unlike the brain that doesn't have a lymphatic system,
we have to have another system in addition to blood supply,
to provide nutrients to the brain and remove waste.
And that happens to be the ventricular system
and cerebrospinal fluid.
Well, once the cerebrospinal fluid has circulated
throughout not only the outside of the brain
but we'll see later within the brain
in structures called ventricles,
all the waste products have to be taken back
into the venous circulation,
the unoxygenated blood
that's going to be going back to the heart.
And one of the ways it does that is through
these blood vessels here.
These blood vessels are veins
that are taking
unoxygenated, waste-filled blood
from the brain and returning it to the heart.
Now unfortunately, you could see
that there's a little bit of space here
before the veins connect
with the structure here called the sinus.
The sinus is a blood-filled cavity
that contains unoxygenated venous blood
going back to the heart.
We also said that the brain is sitting
inside of cerebrospinal fluid.
So if the brain moves too much,
it's possible that you could tear, damage those vessels,
and what you would have is a sub,
under, dural hematoma.
And in the next specimen, we'll show what happens
when you have a subdural hematoma.
So this is an example of a brain
that experienced a subdural hematoma,
and what you can see is that the blood is filling in
all the crevices of the brain.
While this looks extremely bad,
in reality this is not as bad as another type
of hematoma called an epidural hematoma,
epi being outside of the dura.
Because at least here we've got two benefits.
Number one, this is low-pressure venous blood.
This is unlike arterial blood,
high pressure coming out of your aorta,
taking blood to the brain.
Second benefit is because it's under the dura,
it can fill in all the spaces here,
and it really doesn't cause too many neurologic deficits
until all the spaces here become filled.
And then the brain can't hold any more volume.
And what ends up happening,
the brain ends up pressing down
through the tentorium cerebellum here,
'cause we said the tentorium cerebellum,
and it pushes down on this region of the brain stem.
This region of the brain stem
is called the medulla oblongata,
and what it is responsible for is
for regulating your heartbeat and breathing.
And if you don't stop the bleeding in the brain here,
you will end up with a herniation and die.
And this is what likely happened to this patient.
Now that we've covered the spinal cord,
we'll spend the majority of our time discussing
the four remaining divisions of the central nervous system,
the cerebrum, which is the largest part,
as we said earlier,
the diencephalon cannot be seen from the outside,
the cerebellum, shown here,
and the brain stem,
shown here.
So first, let's focus on the cerebrum.
One of the first things that I hope you can appreciate is
that the cerebrum is divided
into a left and a right hemisphere
and that they are divided here
by this long, deep depression
called the longitudinal
or interhemispheric fissure.
So the first concept that I want
to talk about at the cerebrum is that
the left hemisphere controls the right side of the body
and the right hemisphere controls the left side of the body.
So when you put your right hand on something,
all of that information is going to be perceived
by the left hemisphere.
If I turn the cerebrum this way,
you can see that the cerebrum
has these depressions
and ridges.
The depressions,
a single depression is called a sulcus,
multiple depressions are called sulci.
The ridge is called a gyrus,
or multiple are called gyri.
And these depressions and ridges actually mean something.
They contain functionally relative information.
So if we look at the major depression,
this major depression right here,
this depression is called the central sulcus.
And the central sulcus is what divides
the frontal lobe from the parietal lobe.
So now we can talk about the lobes of the brain.
We have four major lobes,
the frontal,
the parietal,
the occipital,
and down here the temporal low.
And we also have another fissure here.
A deep depression is a fissure.
And this is called the Sylvian fissure
or the lateral fissure.
And what the lateral fissure
or Sylvian fissure does
is separate the frontal
and parietal lobes from the temporal lobe.
Now, notice the shape of the temporal lobe
because the shape of the temporal lobe
will be a great landmark for you to be able to determine
whether you're looking at the right hemisphere
or if you're looking at the left hemisphere.
Even if I took off the cerebellum and brain stem
and you had no opportunity to use the cerebellum
as a landmark for what's the back of the brain
and the front of the brain,
you should be able to look at the shape
and pointiness of the temporal lobe
to see that this is a left hemisphere.
So if we focus in more
on the various sulci,
we can say that if this
on the left hemisphere
is the central sulcus,
then the bump right in front of the central sulcus,
we call the precentral gyrus,
pre because it's before.
And this gyrus contains the motor information.
It doesn't contain alpha motor neurons
that are innervating your skeletal muscle.
These motor neurons up here we call upper motor neurons.
These are the command neurons.
These are the neurons that are going to tell your muscles
in your arm and your legs to move.
They're the high command center.
Right in front of the precentral gyrus,
you have a triangular region right here
called the premotor cortex,
and the purpose of the premotor cortex is
to plan motor activities.
Really doesn't execute the motor activities.
It makes a plan
and tells that plan
to the precentral gyrus.
And that plan then gets commanded
to the alpha motor neurons in your spinal cord
that then go and innervate the muscle.
Believe it or not, there is a map
of your body within this gyrus.
Where the motor neurons that are going
to be controlling your feet and legs
are deep here in the interhemispheric fissure,
your arms and body
and face are out here.
In addition, within the frontal lobe,
you have another region right about here
that's called Broca's area.
And Broca's area is for the motor component of speech,
not moving your tongue,
but your ability to express your thoughts.
It is motor.
Now, what's interesting is
that Broca's area is located very, very close
to the tongue and mouth region of your motor map.
But again, I want to make sure that you understand
that if you have an aphasia, the inability to speak,
it has nothing to do with the inability
to move your tongues and lips.
It's your inability to express yourself.
So this is the motor component of the frontal lobe.
The vast majority of the frontal lobe here
is called the prefrontal cortex.
And the purpose of the prefrontal cortex is limbic,
limbic functions like your personality,
storage of long-term memories,
deciding what is right and wrong,
regret, motivation,
all these things that define you as being you.
So when I hold this person's prefrontal cortex,
this is all the experiences that that person ever had
being stored here in the prefrontal lobe.
If we go back behind the central sulcus,
the gyrus that is right behind the central sulcus
is called the postcentral gyrus.
And the purpose of the postcentral gyrus
is somatosensory information,
soma coming from the root body.
Right, so this is body information.
This is where the sensory information
from your right side of your body will end up
since this is a left hemisphere.
And just like I said there is a map,
a homunculus,
for motor information,
there is a map in the postcentral gyrus
for somatosensory information.
Basically the entire parietal lobe is exclusively
for somatosensory information.
Similarly, if we look back here to the occipital lobe,
the occipital lobe is purely for visual information.
So I joke when I go out
and do elementary school lessons on the brain,
that, yes, you indeed have eyes at the back of your brain.
The fourth lobe down here is the temporal lobe,
and we'll see that there are two very important components
of the limbic system here in the temporal lobe.
You have the amygdala deep down within here
that's involved in emotion,
and you have the hippocampus,
which is involved in learning and memory.
Another important component of the temporal lobe,
right about here, right where your ears would sit,
is this is where the primary auditory cortex is located.
Interestingly, right here within the parietal
and a little bit of the temporal lobe
is another language area called Wernicke's area.
Wernicke's area, interestingly,
is near the primary auditory cortex,,
but individuals that have Wernicke's aphasia are not deaf.
They just can't comprehend
or understand speech.
They'll be able to speak fine.
They might misuse words.
But the bottom line is here
that this is a sensory
or receptive aphasia,
whereas Broca's aphasia is an expressive
or motor aphasia because they can't express themselves.
Other component of the cerebrum,
now we're looking at the underside,
is we can see here,
the temporal lobes,
and you can see the brain stem.
There are three components to the brain stem,
the midbrain,
this big, bulgy part here, the pons,
and this smaller part here that will be contiguous
with the spinal cord, the medulla.
And we'll have an entire laboratory
devoted to the brain stem.
The last component is the cerebellum.
And just like the cerebrum
has a left and a right hemisphere,
you can see that the cerebellum
has a left and a right hemisphere.
Now, what's important to understand here
about the cerebellum is that the purpose
of the cerebellum is balance and coordination.
So you make a motor plan,
and you decide you want to do something.
That information, do something,
is not only going to go to the motor neurons
in your spinal cord so that you actually do what you want.
That information will also go here to the cerebellum.
So as you start to do whatever it is you want,
sensory information will be coming into the cerebellum.
And the purpose of the cerebellum is to compare
what you want to do, what the motor plan is
with what you are actually doing.
And if you're not executing a good motor plan,
then it's the purpose of the cerebellum to fix that.
An important concept about the cerebellum
is that if you have cerebellum damage,
you will see a neurologic deficit
on the side that you have the damage
because the cerebellum is unable to fix
what you are doing wrong.
Whereas if you have damage to the cerebrum,
a stroke on the left hemisphere will give rise
to neurologic damages on the right,
and a stroke in the right hemisphere will give rise
to neurologic damages on the left.
Now what we want to do is cut the brain in half
because the one thing we can't see
from the outside is the diencephalon.
So now what we're looking at is a midsagittal cut
of the brain.
I'll flip the brain over for a second
and ask you to decide
whether I'm holding a right hemisphere
or a left hemisphere.
This is the right hemisphere.
Notice the shape of the temporal lobe
and the fact that we have the cerebellum here at the back.
If I flip it over, another way that you can tell
that it's a right hemisphere is the shape
of this structure right here.
I said earlier that the left hemisphere controls
the right side of the body
and the right hemisphere controls
the left side of the body.
So we must have some structure
that allows the left hemisphere
and the right hemisphere to communicate,
and that happens to be the corpus callosum.
Another way that you can tell
that this is the right hemisphere
is look at the shape of the pons and the cerebellum.
And when you look at the pons and the cerebellum,
you can see this space here.
So this is now one structure that we can see
that we weren't able to see before,
and that happens to be the ventricular system.
The ventricular system represents a series
of fluid-filled structures.
So this mold
is actually plastic,
but what it's showing is the shape of the ventricles.
This is really cerebrospinal fluid,
and this would sit in the brain just like this.
So if I push on this,
you might see some cerebrospinal fluid
coming out of this hole here.
And the reason why is you have two lateral ventricles.
You have one in the left hemisphere
and one in the right hemisphere.
And what they do is they drain
by this small hole here
into the third ventricle.
The third ventricle
is this space shown right here.
The third ventricle is the perfect landmark
for the diencephalon.
So this space,
this neural tissue right here,
is the diencephalon.
From the third ventricle, the cerebrospinal fluid drains
through a very small canal here
called the cerebral aqueduct.
From the cerebral aqueduct,
it drains into the fourth ventricle.
From the fourth ventricle,
it goes out through
the subarachnoid space,
all the way around the brain,
and, as we saw earlier,
to a dural sinus
and back into your general circulation.
So now the question is we have cerebrospinal fluid,
where does the cerebrospinal fluid come from?
And the cerebrospinal fluid is made
from this tissue called choroid plexus.
So the choroid plexus is blood vessels
and specialized cells that withdraw substances
from the blood and put it into the cerebrospinal fluid
to deliver to the brain.
So the diencephalon here
has three major parts.
It has the thalamus.
The thalamus is considered a sensory relay.
All sensory information and motor information is going
to end up going through the thalamus.
Under the thalamus,
this small triangular piece of tissue here
is called the hypothalamus,
hypo for being under.
The one thing that I want you to think
about the hypothalamus is homeostasis,
homeostasis or thermostat.
This is going to regulate all of your autonomic function,
how much sleep,
whether you're thirsty, whether you're hungry,
all the functions that you don't have to think about,
whether you're hot or cold.
Think of it as homeostasis or a thermostat.
The third component is actually a gland located right here.
This is called the pineal gland.
We'll talk about the pineal gland later,
but the purpose of the pineal gland is to make melatonin.
And because of its connections with the hypothalamus,
it regulates what are called circadian rhythms,
circa diem, about a day.
Most important one is sleep
because this gland makes melatonin,
and melatonin is responsible for maintaining sleep.
The other thing I think you can appreciate
in this sagittal view is the three parts of the brain stem,
the midbrain,
this huge, bulgy pons,
and then the medulla.