What I'd like to do today is to give you a little bit of background about how the brain works in both health and
in disease, for example.
It's kind of amazing to think about. How is it that I can sit here and spontaneously speak to you without actually
pre-planning a whole lot of what I'm about to say? How is it you converse with your friends and neighbors?
Just by taking what they have to say,
inculcating it into your own brain, and coming out very quickly with information.
How is it that you move?
How is it you develop a physical skill like dancing or being a better basketball shooter?
And how is it we remember things well? How is the brain organized? Let's start with this
plastic brain. Here's a skull, and inside the skull,
surrounded by spinal fluid that cushions it, is the brain. The brain is divided into a right side and a left side,
and then into lobes, so this is the right hemisphere,
this is the left hemisphere.
The lobes consists of the frontal lobe, which is more anterior--
this area is important for what we call executive functions and memory.
Learning helps us plan helps us sequence, helps us think through our ideas.
Most other living things don't have as much frontal lobe as we have, and so we're supposed to be better thinkers
than other things that live on Earth.
Then there's the parietal lobe that's primarily involved in sensation, and where we are in space,
helps us integrate information. We have the temporal lobe, which is a banana-like area underneath the frontal and parietal lobes,
that contains how we hear, contains,
deep inside, the hippocampus for memory,
that's essential--we'll come back to that a bit later--
as well as language functions.
And then we have the occipital lobe in the back that takes information from vision up here, sends it through
optic nerves, back to the brain to allow us to see. Then, under the brain, what we see is the
typical Belem,
which helps us with our coordination and timing of things, and then we can see here the brain stem,
and then finally, here's the spinal cord the brain stem contains.
Especially--
not only is it a conduit between the spinal cord and our muscles and
sensation and the brain, but it also contains our regions for consciousness, for breathing, for hyper-
managing our blood pressure, and so a small amount of damage in that brain stem would make us
comatose, and
the spinal cord that contains the nerves that eventually go out to the muscles to help us contract our muscles
as well as bring in information from our joints, from our muscles, from our skin, about
feelings of temperature, feelings, of pain,
feelings of movement, and
help the brain integrate all that
information. We can see the inner sides, and it's a little bit easier now to see the
cerebellum in the back, the
brain stem, and then leading to the beginning of the spinal cord, which of course is cut off, but would go down your back, and
we can appreciate the frontal lobe here and the inner side.
In fact, this area right in here, in the back part of the frontal lobe,
contains the nerve cells for the leg, and this part, in the outer side, contains the nerve cells for the hand and arm.
For movement and back here, we can see that occipital lobe that allows us to see--not only
see, but begin to interpret motion, color,
size, and
speeds of movement, so within that ribbon of cortex that we saw in the human brain are
many billions of neurons, and this is kind of a picture of a neuron, with its
nucleus, and then it sends out processes called dendrites, often sends out one large process called an axon.
We can see that in purple there are other
neurons that send out dendrites and axons to connect to these
spidery tree limb-like branches here, and this is the way nerve cells make their connections together.
Then as that axon comes out, it develops a white, glistening material called myelin
from other cells that make myelin, and that helps it conduct electrical impulses that eventually go down and connect to
perhaps a nerve cell in the spinal cord, or a nerve cell in another part of the brain.
Then at the places where these nerve cells
make their connections with each other,
we have what's called a synapse. The synapse contains chemical
messengers that are sent out from that
dendrite or axon and travel to the opposite
nerve's dendrite or axon, and
with that, can trigger an electrical impulse.
But this is the real working area, the synapse. By strengthening connections
between one
nerve ending and another nerve ending,
we, in a sense, create the basis for learning. We reinforce our
ability to make those connections,
and this is where we kind of cement our learning. When many, many hundreds of thousands, millions and even billions of neurons
work together,
they fire together, and
in a general way that leads to
more likelihood that they'll fire together, and that's what we mean by
learning.
So here we have a
real human brain. It has a protective covering called the dura that sits up against the skull and
helps protect the brain from trauma. And then under the dura is
another fine layer called the
arachnoid, and under that, subarachnoid space, which
also serve protective effects as well as help bring blood vessels into the brain.
Here, we see the front part of the brain, the frontal lobe.
So all this here, the parietal lobe in here,
the occipital lobe here,
on the right side here's the cerebellum underneath for balance, and here we see again
the brain stem and the spinal cord, so
we've seen the whole brain, the right side, on the left side we've talked about the lobes,
but what goes on in the brain has to do with clusters of nerve cells and their
pathways called axons that are moving in many directions within the brain. So, let's take a slice of this brain. Let's
go as if we
cut across
the middle and we pulled out a
slice of the brain, so now what we have is the frontal lobe and the back part of the brain, here.
We're still in part of the parietal lobe
because of the angle of the cut, and deep inside we can see that there's spaces called ventricles, and
these produce spinal fluid that then comes outside of the ventricles and surrounds the brain.
But you can see that there are different shadings here.
Here's--that what's called the caudate nucleus.
We have here the thalamus, we have here the
internal capsule.
Each of these carries certain fibers. For example, the thalamus has nuclei, which are important for memory. If you damage
the upper and inner parts of the nerve cells that are deep in there,
merely a few hundred thousand of them, you may not be able to remember anything if
you damage them. Another part of the thalamus that brings sensation up from the muscles and from the
skin, joints of the body, you may not be able to feel anything.
You may not be able to tell whether something is hot or cold or
sharp or dull, or you may not understand whether you're moving your wrist up or down.
You may not understand or recognize the direction of a movement.
if you damage this tiny area in here,
called the internal capsule,
which is lighter than the grayer areas around it, this is kind of a funnel, so information coming from the
leg and arm region of the brain up above
comes down as a funnel and passes through here,
so a tiny stroke, as little as
1/4 to 1/2 an inch in this little area, lack of blood flow to the small area there or trauma
from hitting your head, and perhaps not wearing a helmet and getting a head injury can cause paralysis from the tiniest little injury there.