Okay. Now let’s move to our counterpart,
which is the central nervous system.
So like I said, it’s made up of
the spinal cord and the brain.
The brain has three main subdivisions,
the hindbrain, midbrain, and forebrain.
So there are also the older
names that have been used,
the rhombencephalon, the
mesencephalon, and prosencephalon.
You should probably
know those for the MCAT
because they might not refer
to them as hindbrain.
They most probably will, but they might
also throw around these other name,
so you should kind of associate
which one goes with which.
The entire CNS is
contained within this sac
and it’s bathed in this solution
called the cerebrospinal fluid or CSF
and it’s basically a salt
solution so it’s saline.
We say it’s a circulating
which provides all the different
nutrients, protection, and removes waste.
So nutrients make sense
because it’s bathed in stuff
and it has all the ions, the sodium,
the potassium, the calcium,
and all those things that it needs.
And it provides protection because the brain
actually sits floating inside the skull,
inside different layers of membrane
and this cerebrospinal fluid.
So the analogy I like to use is think
of maybe a large container of soup
or something like a metal tin
and if inside that you
put a water balloon
and then you fill that up with a little
bit of water and put the lid back on.
So that would sort of
represent the skull and brain
with the outside of that
hard tin being the skull,
then you have your brain
which is the water balloon,
and then you have water and that
kind of allows it to float around.
And you want that because
if there was not CSF,
you would have your very tender,
soft, malleable brain tissue
against this rigid, hard skull
and just walking
around or dancing,
you basically would be causing major brain
trauma, which you don’t want to be doing.
So by having this kind of floating system,
it allows it that buffer
and that ability to
deal with a lot of the movement
and impact that we deal with.
Here’s the basic structure,
again, not a lot of components.
We have the brain, we have the spinal
cord, and then we have everything else,
which is the peripheral nervous
system, we have the ganglion cells,
and we have all the nerves that exit the
spine going to all the different effectors
and getting sensory information as well
that goes up to the spinal cord --
up through the spinal cord to
the central nervous system.
So easy divide. Brain, spinal cord,
CNS; everything else is PNS.
Here’s a nice blowup
of the spinal cord.
It shows that it’s actually a
stacking of different bone segments
and each one is separated by
some tissue and cartilage
and there’s a cavity that allows these nerves
to go in and to go up to the spinal cord.
So it’s connected to the brain and
is protected by the CSF as well,
so it also has the same fluid
and has a vertebral column.
This is the pathway for sensory
data to go to the brain
and it allows for integration
and processing up at the brain.
There’s some integration and processing that
actually happens in the spinal cord too.
So as things come
in, they synapse,
and you’re starting to see some
integration happen right on the spot.
And it’s also responsible for
simplest spinal reflexes
like the muscle stretch
reflex which we talked about.
So it prevents it from having to
go all the way up to the brain.
It can happen right there at the synapses
happening within the spinal cord.
Now let’s take a look at
some of the structures in
each of those different
regions that we talked about.
We’ll start with the hindbrain.
So first off you have
the medulla oblongata.
This is a spot that relays information
between the different areas of the brain.
So it’s sort of like a major hub.
It regulates vital
including blood pressure,
digestive function, vomiting.
So again, these are things that you might
not necessarily be thinking about.
And kind of a simple rule
of thumb that we have
for the brain is the deeper
you are in the brain,
sort of the more rudimentary
or simple the function,
and as you peel that onion
and you go on the outside --
actually, not peel the onion, but add
layers to the onion and move farther away,
the more sort of complex and
higher level the function is.
So the very -- the base of the
brain being simple stuff,
and the very outside or the
cortical layers is where we do
a lot of our executive function
and higher level thinking.
So the pons is a connection point between
the brainstem and the cerebellum
and this coordinates
movement and balance.
So we’re not going to spend tons of
time going through each of these
because simply put you need
to know these structures
and you need to know their
basic function for the exam.
The cerebellum is also
known as little brain
and sort of basically because of
its function and its location.
So we say it’s an integrating center
where complex movements are coordinated.
The midbrain now is a relay for
visual and auditory information.
So this is where a lot of
that input is now coming in.
And it also contains the RAS, which
has come up at other lectures
as the reticular activating system, which
is responsible for arousal and wakefulness.
And the link I always tell people
if you don’t remember think
of arousal or being activated
and this is called the reticular
activating system or RAS.
The brainstem refers to the midbrain
along with the medulla and pons.
So you’ll also hear
that term brainstem,
I mean I myself have
been using it already
and that’s what we’re referring
to actually, is the midbrain
and the medulla and the pons.
Now the forebrain includes the
diencephalon and telencephalon.
And the diencephalon includes structures
like the thalamus and the hypothalamus.
The thalamus contains relay and processing
centers for sensory information,
and the hypothalamus contains
centers for controlling emotions,
autonomic functions, and a major role
in hormone production and release.
So quite a bit of stuff they’re doing,
this is kind of advanced stuff,
so now layering an emotion and
processing actual sensory information.
This is sort of higher level stuff.
Here’s a nice image looking at
all the different components
of the central nervous
system as a whole
and there’s a few that
I want to highlight.
One, the locations of the structures
that we’ve already talked about,
so the hypothalamus, the midbrain,
the cerebellum, the brainstem.
I want you to also notice how
the spinal cord comes up
and then is connected to the brainstem and
it’s kind of at the base of the brain.
And we have something
called the corpus callosum.
Corpus callosum, this
is also very important.
And this is a bundle of fibers that
connects the two hemispheres of the brain.
So we haven’t gotten there yet, but basically
the brain is made up of two halves.
I’m sure you’ve heard of that
before, left brain, right brain,
but there’s actually a physical clear
marcation between the two sides of the brain.
The two hemispheres are connected,
one of the connections is
through this corpus callosum.
So here’s an image looking at, you
know, an animal model of the brain
and you can see as you
spread the hemispheres apart,
you can clearly see
the corpus callosum.
So it connects the two
In this diagram you also can see the
location of the cerebellum, as well.
Now the two sides have some differences.
So generally speaking, both
hemispheres have similar functions,
but there’s a little bit of
differentiation in each.
So for example, at the rear of
the brain at the occipital lobe,
we know that that lobe is primarily
dealing with visual function.
Now, the left and right side of the occipital
love both deal with visual function,
but they might control and modulate and
mediate different aspects of vision.
So the hemispheres are bilateral,
meaning two sides, left and right.
The left side of the brain controls
the motor function of the right side,
and the opposite holds true.
So when I’m moving right hand I’m
actually using the left side of my brain,
and when I’m using my left hand I’m
using the right side of my brain.
So information is crossed.
The left hemisphere is generally
responsible for speech,
while the right hemisphere is responsible
for visual-spatial reasoning
and for interacting with things like music,
a little bit more of the artsy side, okay?
So here are the lobes,
you’ve seen these before.
You should be very familiar with
their location and their names.
So the frontal lobe,
top of the hat,
it’s nice to meet you and
you’ll remember that
because it’s at the front
of your brain, okay?
Then we have the occipital lobe
which is at the back of the brain
and this is the part of the brain
that deals with visual function.
And then we have the parietal lobe
which is kind of in between the two.
And then the temporal lobe if you want to
remember is where your temples are, okay?
So you should know their locations.
Now the frontal lobe initiates
all voluntary movement,
complex reasoning, problem solving.
So the prefrontal cortex,
the frontal lobe,
these are all areas that kind of
do that higher level thinking,
deal with emotion, help
shape your behavior.
The parietal lobe is involved in general
sensation and taste, gustation,
so it’s more around
and this is also where we have the
somatosensory cortex and the homunculus
which we’ve talked about in
some of the other lectures.
The temporal lobe processes
auditory and olfactory sensation
and it deals with short-term
memory, language, comprehension,
and is also involved
So you can see that certain
parts of your brain are very
localized and focused
on a specific function
and now they’re a little bit more
diverse and do quite a few things.
Occipital lobe, an
example of being pretty
focused in dealing with
just visual information.
Now, how do you study the brain?
Well, there’s a lot of ways of doing it.
So you can have two broad categories.
Invasive is when you’re actually
going and poking and prodding,
there’s noninvasive where you’re
looking at usually a more behavioral
or indirect measures and we’re
also looking at in today’s world
some of the cool bio-imaging
that we now have
and you’re not drilling holes
and opening up the skull.
So you can also have the scenario of
some of this being behind damage, right?
So you can look at the effect
of brain damage or injury
and this is what we call
a natural experiment
because hopefully you’ll
have some information before
or you might have normal function,
and then you have some type of
injury, a stroke or trauma,
and then you can look at
what’s happened post-trauma.
How was this changed?
Look at the changes in behavior,
and you can look at
functional changes, as well.
You can also have, say, maybe postop if
it was a significant trauma like death,
you could look at a biopsy data,
where you’re looking at
histological and pathological data,
so looking at cross-sections of brain,
staining, looking under a microscope,
and looking at “Oh, I’m seeing this.”
So again, you’re looking
hands on at what’s happened.
You can have a look at
looking at actual psychotropic
or brain-changing agents.
You can look at ECT, which is
You can look at conduction
stimulation looking at electrodes.
You can look at different animal models.
This is really the bulk of where a
lot of medical research is done.
We can have chemical/electrical
simulation through EEG
and the example that we used
was looking at recordings
from when you’re looking at
different stages of sleep
and they were capturing electrical activity
and it allows us to understand function.
And then more recently and
much more cool is bio-imaging.
So things like CT scans, PET scans,
MRIs which uses magnets,
magnetic resonance imaging,
and we have a lot of really
new cool hybrid techniques
to image the brain
without having to go in
and they can do that at
such higher resolution
that can go down right down
to the cellular level.
And they can look at presence of
anomalies like tumors or growths.
We can look at internal bleeding.
We can look at so a stroke.
We can look at a function,
changes in glucose utilization.
So how active is that area of the brain,
really, really cool stuff in order to study
the brain and understand its function.
So let’s take a look at the
influence of neurotransmitters
and how they impact behavior.
So we’ve explained what a neurotransmitter
is, we’ve explained the process of release.
Now we’re going to look at the
and what impact they actually
have on our behavior.
So transmitter release and the
impact that they have on behavior
can be attributed to three things
that we want to talk about right now.
So one is genetics, the
second is lifestyle,
and the third is injury or disease.
Let’s start with acetylcholine.
It is involved with voluntary
movement, memory, learning, and sleep
and we know that we have elevated
levels in certain individuals
that are expressing depression, and we
also have low levels can cause depression.
So this is one that has kind of a lot of
range and does a lot of different things.
Dopamine is really, really popular
when we’re looking at behavior.
So it is a happy transmitter.
It causes feelings of pleasure,
it can help modulate voluntary movement,
it’s associated with learning.
And what it does is it actually
activates the reward area,
an area within the limbic system
called the dopamine reward pathway.
And we know that if you are doing
something that’s positively reinforcing,
so a good behavior, you see
a release in dopamine.
If you happen to maybe snort some
cocaine or take some heroine,
that also causes a change in levels
of dopamine in the reward pathway
making that a behaviorally
so you want to continue to do that
positively reinforcing behavior.
And some examples in terms of inappropriate
levels and the effect on behavior,
we can have schizophrenia, Parkinson’s,
disorders that we’ve mentioned,
and that’s linked to inappropriate
levels of dopamine.
Norepinephrine causes arousal, alertness,
and may stimulate the
sympathetic nervous system.
So we know lower levels
can cause depression
and it can be linked to changes
in terms of stress hormones.
So serotonin is the last one
that we want to mention here
and directly linked to anxiety
and it’s typically regulating things
like appetite, sex drive, and mood.
So what we’re trying to
show here is a clear link
between a transmitter
and the behavior.
So there is obviously a lot
of impact that you can have
if you’re changing the levels
of this neurotransmitter,
whether it’s a through pharmacotherapy,
taking medicine, using recreational drugs,
or even things like changing your
diet can have a dramatic impact
in the levels of neurotransmitter
and the ultimate behavioral effect.