Description

Telencephalon

• Pallium
  • Cerebral Cortex
  • White Matter of the Brain (Corpus Medullare Telencephali)
• Subpallium
  • Basal Ganglion

White Matter of the Cerebrum

• Association Fibers
• Commissural Fibers
• Projection Fibers

Association Fibers

• Short Association Fibers
  • Arcuate Fibers (Fibrae Arcuatae)
• Long Association Fibers
  • Superior Longitudinal Fasciculus (Fasciculus Longitudinalis Superior)
  • Inferior Longitudinal Fasciculus (Fasciculus Longitudinalis Inferior)
  • Uncinate Fasciculus (Fasciculus Uncinatus)
  • Cingulum
    • From Frontal and Parietal Lobe to Parahippocampal Gyrus (Gyrus Parahippocampalis)
    • Papez Circuit

Commissural Fibers

• Corpus Callosum
  • Splenium
  • Truncus
  • Genu
  • Rostrum
  • Minor Forceps / Frontal Forceps (Forceps Frontalis s. minor)
  • Major Forceps / Occipital Forceps (Forceps Occipitalis s. major)
  • Radiation of Corpus Callosum (Radiatio Corporis Callosi)
• Commissure of Fornix
  • Connects two parts of Fornix together
    • Crus of Fornix
    • Body of Fornix
    • Column of Fornix
• Anterior Commissural Fibers (Commissura Anterior)

Projection Fibers

• Internal Capsule (Capsula Interna)
  • Anterior Limb (Crus Anterius)
    • Frontopontine Tract (Tractus Frontopontineus)
  • Genu
    • Corticonuclear Tract (Corticobulbar Tract)
  • Posterior Limb (Crus Posterius)
    • Corticospinal Tract (Tractus Corticospinalis)
    • Thalamocortical Fibers (Fasciculi Thalamocorticales)
    • Temporopontine Tract
    • Parietopontine Tract
    • Occipitopontine Tract
    • Optic Radiation (Radiatio Optica)
    • Acoustic Radiation (Radiatio Acustica)

Basal Ganglia

• Caudate Nucleus (Nucleus Caudatus)
  • Head (Caput)
  • Body (Corpus)
  • Tail (Cauda)
• Putamen
• Striatum
• Globus Pallidus Externus
• Globus Pallidus Internus
• Lentiform Nucleus
• Thalamus (Ventral Anterior and Ventral Lateral)
• Subthalamic Nucleus
• Substantia Nigra
• Amygdaloid Body
• Claustrum

Sources used in this video

• Memorix Anatomy 2nd Edition by Hudák Radovan (Author), Kachlík David (Author), Volný Ondřej (Author)
• Biorender
• University notes and lectures

Transcript

Introduction
0:03
What’s up. Meditay here. Let’s now cover the Internal structures of the cerebrum,
0:08
underneath the cerebral Cortex. So the central nervous system
0:11
consists of two parts: the encephalon and the spinal cord. The encephalon
0:16
is then further divided into specific parts. We have the brainstem, which consists of
0:20
the medulla, pons, and the midbrain or the mesencephalon. We have the Cerebellum back here,
0:25
then the diencephalon and the Telencephalon. Our focus in this video is going to be the
0:29
telecephalon, which is this blue part here. But If we change this picture into a little
0:34
more realistic one, we’ll find the spinal cord, the medulla, Pons and the Cerebellum.
0:39
And then the Telencephalon would be the whole blue area right here.
0:43
Let’s now make a vertical section just like this, cut it, and then look at the brain from
0:48
this perspective. We’ll see this. SO this is what we call a coronal section of the brain,
0:54
and what we can see here is Pons and the Midbrain, which are a part of the brainstem, and the
0:58
diencephalon. The rest of the tissue you see in front of you now is what is referred to as the
1:02
Telencephalon, which is Latin for the cerebrum. When you look at the cerebrum, you’ll notice
1:07
straight away that it consist of two hemispheres. So the Right Hemisphere, and the Left Hemisphere.
1:12
And each of these two hemispheres is divided into two specific parts: the Pallium
1:18
and the Sub-Pallium. The Pallium is sort of the two outermost layers of the brain,
1:23
which is the Cerebral Cortex, on the surface here filled with nerve cell bodies,
1:28
and the white matter that is just underneath the cerebral Cortex formed by myelinated axons.
1:34
The subpallium consists of what we call the Basal Ganglia, which are nuclei located in the
1:39
deep white matter of the Telencephalon. So again, in this video, we’re going to
1:43
focus on the White matter of the brain, and the deep grey matter structures, the basal ganglia
1:48
So in this video, we’re first going to first look at the three types of fibers that make
1:52
up the white matter of the brain, which are the Association fibers, Commissural fibers,
1:57
and Projection fibers. After that, we’ll cover the actual anatomy of the basal ganglia.
2:03
In our last video, we covered the anatomy of the cerebral Cortex,
2:06
so go ahead and watch that if you haven’t, because I highly recommend you to have an
2:10
understanding of the cerebral Cortex before understanding what’s underneath it. Alright.
White Matter of the Brain
2:16
So the Cerebral white matter is classified, or divided,
2:19
into three systems of fibers. The first one is the Association fibers. These fibers connect different
2:26
structures within the same Hemisphere. We have something called Commissural
2:30
fibers that cross over to the other side and connect structures of one Hemisphere with
2:34
the other. So right Hemisphere connects with the left Hemisphere and vise versa
2:39
Then we have projection fibers. These are fibers that project downwards and upwards
2:44
from or to the cerebral Cortex, through the brainstem and the spinal cord.
2:48
So these are the three fibers we’re gonna focus on, and we’ll start with the association fibers.
Association Fibers
2:53
These fibers, as we said, connect structures within the same Hemisphere, so let’s go ahead
2:58
and look at a side view of the brain so that we get a better overview of these fibers.
3:02
So the Association fibers are divided into two types. These are Short
3:06
association fibers and Long association fibers. The short association fibers consist of Arcuate
3:13
fibers. And as you see here, they connect neighboring gyri or areas together. And so
3:19
they’re short, and as you see here, they form this “U shape”, that’s why in some sources,
3:24
you might see the Arcuate fibers being referred to as the U-Fibers. So that was the only short
3:29
association fibers we have in the white matter. Long association fibers consist of the Superior
3:35
Longitudinal Fasciculus. These fibers connect the Frontal Lobe with the Occipital and Temporal Lobe.
3:41
Then we have the Inferior Longitudinal Fasciculus that passes the lower surface of each Hemisphere
3:47
and connect the Temporal lobe and the Occipital Lobe together.
3:50
After that, we have the Uncinate Fasciculus, which passes along the bottom of the lateral
3:55
sulcus as you see here, and connect the Frontal Lobe with the Temporal Lobe.
4:00
Then we have the Cingulum, and the Cingulum is best seen if we look
4:03
at the medial surface of the Hemisphere. So here in blue, we have the Frontal Lobe,
4:07
and behind that, you see the Parietal Lobe. And under here, we have the Cingulate Gyrus. The
4:13
cingulate gyrus is considered a part of the limbic system because it works by transmitting fibers
4:19
or signals. So the Cingulum is fibers that go from the Frontal lobe and the Parietal Lobe,
4:24
through the Cingulate Gyrus and eventually into the Parahippocampal Gyrus. As well as
4:29
sending some fibers towards the temporal lobe as well. The Cingulum is a part of the Papez
4:34
Circuit. Remember we talked about this one when we talked about the anterior nuclei of the Thalamus?
4:39
Papez circuit is related to emotional episodic memory, so the Cingulum has fibers circulating
4:45
around in the subcortex to remind you about previous episodes you’ve had and
4:50
connect it with the frontal lobe to trigger an emotional response to these previous memories.
4:55
So that was the Association fibers. Next, let’s do the Commissural fibers!
Commissural Fibers
5:00
Now there are three ways fibers can cross over to the other Hemisphere or three structures that the
5:05
association fibers form as they pass over to the other side. And these are the Corpus Callosum,
5:11
Commissure of Fornix, and the Anterior Commissure. So let’s dig a little deeper into their anatomy.
5:17
The corpus Callossum is located here, so as fibers cross over to the other side,
5:22
they form the Corpus Callosum. Now the corpus callosum consists of
5:27
different parts. So if w make a vertical section of the brain and then look at it from the side,
5:32
we’ll see this. So what do we see here?
5:34
We see the frontal lobe and the Parietal Lobe. We can see the Cuneus, which is the primary visual
5:39
Cortex. We see the Lateral Occipitotemporal Gyrus and the medial occipitotemporal gyrus.
5:45
So these three are a part of the occipital lobe. Then we can see a part of the Temporal lobe down
5:51
here, the inferior temporal gyrus. And then here in blue is the parahippocampal gyrus, and
5:56
then our Cingulate Gyrus here. Now underneath the Cingulate gyrus, we’ll find our Corpus Callosum.
6:02
And now, just to orientate, you’ll find the Septum Pellucidum right underneath it.
6:07
This septum is a double fold of membrane that separates the Lateral ventricles from each other.
6:12
And it goes from the Corpus callosum down to the Fornix. Cool, now that we have the orientation
6:17
sorted, let’s focus on the corpus callosum. Corpus callosum has an arched shape, as you
6:23
see here. The posterior end is the thickest part, and it’s called Splenium. Anterior to it is the
6:30
Truncus, then the forward bent part is Genu, Genu means knee since it looks like a bent knee. And it
6:36
continues into a narrow part, called the rostrum. So these are the parts of corpus callosum,
6:43
and again they’re fibers that go from one Hemisphere to the other, but the fibers that go
6:49
forward into the frontal lobe have a unique name. They’re called Minor, or Frontal Forceps. And the
6:55
fibers that extend back towards the Occipital lobe are called Major, or Occipital Forceps.
7:02
Now, if we go back here. What we really see here from this view is most probably the Truncus of
7:08
Corpus callosum. And when fibers have crossed over to the other side, they radiate spread
7:13
to different parts of the cerebral Cortex, forming the radiation of corpus callossum.
7:18
So that was Corpus Callosum. Awesome. Now, what was this thin stalk extending
7:23
down from corpus callosum called, do you remember we mentioned this earlier?
7:27
This is called Septum Pellucidum. That means that the structure underneath it is called the…
7:33
Fornix. And the commissure of Fornix is what connects the Right side of Fornix
7:37
with the left side of Fornix. But what is the Fornix?
7:41
So if we go back to this view. Here is the Septum Pellucidum,
7:44
lying between Corpus Callossum and the Fornix. But here, you only see a tiny part of the Fornix.
7:51
If we continue backward, you’ll see that the Fornix looks like this.
7:55
One part goes to the right, and one part goes to the left. And the commissure of Fornix is what
8:00
connects both sides together… as you see here. Now, if we hold the Fornix and pull it out.
8:06
You’ll see that it look like this. Now, this whole thing is not really Fornix.
8:11
The green part here is the Hippocampus, and the two bulbs you see here are the mamillary bodies.
8:17
The rest that is not highlighted is the Fornix. So the Fornix what it does
8:22
is it connects the Hippocampus, which is where new memory and learning takes place,
8:26
to other components of the limbic system, like the mammillary bodies. And the Fornix consists of
8:31
several parts. It consists of the Crus of Fornix, a body of Fornix, and a column of Fornix. And in
8:38
between the two parts of Fornix. That is where you’ll find the Commissure of Fornix. Awesome.
8:45
So that was 2/3. The last one is the Anterior commissural fibers, which are small bundles of
8:51
white matter fibers that connect the two hemispheres together across the midline.
8:56
And it lies here, this tiny little structure here, in front of the column of Fornix and the
9:01
3rd ventricle, this tiny structure is the anterior commissural fiber.
9:06
So that was the commissural fibers as well. Next, let’s do the projection fibers.
Projection Fibers
9:11
Projection fibers are ascending and descending tracts, so they’re sensory and motor fibers,
9:17
connect different parts of the cerebral Hemisphere, with all structures under the Cortex.
9:22
And all of the fibers that go to the Cerebral Cortex have to go through a structure called
9:28
the Internal Capsule Which is located here.
9:31
Now from this view, we can’t really have a full overview of the Internal capsule.
9:35
So if we go back to this view. And make a transverse cut, just like this, and then
9:40
remove the upper portion. And then look at the brain from this perspective. We’ll see this.
9:45
So what are the structures we see here? We see the Thalamus of the Diencephalon.
9:49
We see the Caudate Nucleus, which is a part of the Basal ganglia. We see the Putamen,
9:54
and Globus pallidus externus and internus, which are also a part of the Basal Ganglia.
9:59
From this view, we can also see the Lateral Ventricle, which extends all the way to the back.
10:03
We can see septum pellucidum here in the midline. And in the front here,
10:07
we can see the Corpus Callosum. The internal capsule is located
10:11
right about here. So it has the Thalamus and the Caudate Nucleus on the medial side,
10:16
the Putamen, and the Globus Pallidus externus, and internus on the lateral side.
10:21
And again, the fibers that go from the cerebral Cortex and down.
10:24
And the fibers that go upwards to the cerebral Cortex all go through the Internal Capsule.
10:30
It’s kind of like the highway for all fibers going to or from the Cortex.
10:35
And it consists of three parts. It consist of the Anterior Limb,
10:39
or crus anteirus. It consists of Genu, which means knee. And a Posterior Limb, or crus posterius.
10:46
Each part of the Internal Capsule has different tracts that go through it. So the anterior Limb
10:52
has a tract called the Frontopontine tract going through it. And remember, the frontopontine tract
10:58
is one of the corticopontine tracts. So this tract comes from the frontal lobe. It goes down through
11:04
the Anterior Limb of the Internal capsule and then synapses with the Pontine nuclei of Pons.
11:09
From here, it goes to the Cerebellum as the Pontocerebellar tract. Then it goes up
11:15
from the Cerebellum to the Red nucleus, as the Cerebellorubral tract. And then,
11:20
from the red nucleus, fibers either go up to the Thalamus or down as the rubrospinal tract.
11:26
These are extrapyramidal tracts that support voluntary muscle movement.
11:30
So that’s mostly the only tract I wanted to mention that goes through the anterior Limb.
11:35
The tract that goes through Genu is the corticonuclear tract
11:40
And this tract goes from the primary motor cortex and then synapses with the cranial nuclei at the
11:45
brainstem for the voluntary control of muscles located in the head and neck.
11:50
So that is the tract that goes through Genu. The Posterior Limb is the limb that has
11:55
the most tracts going through it. One of them is the corticospinal tract
12:00
The corticospinal tract originates from the pyramidal cells of the primary motor area. And
12:05
since they come from the pyramidal cells, we call this a pyramidal motor tract that descends down
12:10
to the spinal cord to innervate skeletal muscles for voluntary muscle control. So that’s that now.
12:16
Now. Do you remember when we went through the nuclei of the Thalamus? There are tracts that go
12:22
from the nuclei within the Thalamus to the Cortex through the Posterior Limb. And these nuclei
12:27
are specifically the ventroposteriolateral and the ventroposteriomedial nuclei. The tracts that are
12:34
associated with the Ventroposteriolateral nucleus are sensory information for the Trunk and Limb,
12:41
through the Gracile fascicle and the Cuneate Fascicle, and they are responsible for the
12:45
epicritic sensibility, which is proprioception and mechanoreceptors like touch and vibration.
12:50
They will ascend as the medial lemniscus and then go to the VTL nucleus.
12:56
Another tract it receives input from is the spinothalamic tract. And remember this tract
13:01
is responsible for sensation in regards to Pain, Temperature, Pressure, and Touch. That is these.
13:08
The other nucleus, the Ventroposteriomedial nucleus or abbreviated as the VPM. This is
13:14
a sensory nucleus, and it receives sensory information from the Face, as well as Gustation,
13:19
or sense of taste. It receives its senses from the Trigeminal nerve, through the trigeminal
13:25
lemniscus about proprioception, pain, touch, all of those things in the facial region.
13:31
So that is this one. The other one is Gustation, or taste. You know there are specific cranial
13:37
nerves responsible for the sense of taste. These are the facial, glossopharyngeal, and vagus
13:42
nerves. All of them will go the the VPM. And now the tracts that go to Ventroposteriolateral and
13:49
the ventroposteriomedial, will go through the posterior Limb, and then synapse with
13:55
different cortical regions in the brain. And these fibers that go from the Thalamus to the Cortex,
14:00
are called Thalamocortical Fibers. So that is these.
14:05
Now from the lobes of the cerebrum. There are fibers that go from the Temporal Lobe. There
14:10
are fibers that go from the Parietal Lobe. There are fibers that go from the Occipital
14:14
Lobe. And these fibers will go through the Posterior Limb of the Internal Capsule.
14:19
These tracts are called the Temporopontine Tract, Parietopontine tract, and Occipitopontine tract.
14:25
They are very similar to the Frontopontine tract we talked about earlier,
14:29
the tract that went through the anterior limb. And that is because of all of these tracts. The
14:34
temporopontine, occipitopontine, parietopontine and frontopontine tract are called Corticopontine
14:40
Tracts. They’re extrapyramidal tracts that help voluntary movement become more precise.
14:46
And the frontopontine tract is the only one of these that go through the anterior Limb.
14:50
And so these tracts will have the same loop as the previous one. So they’ll synapse with
14:55
the Pontine nuclei of Pons. Then they’ll go to the… Cerebellum as the Pontocerebellar tract,
15:02
and then they’ll go up from the Cerebellum to the … Red nucleus, as the Cerebellorubral tract. And
15:09
then, from the red nucleus, fibers either go up to the Thalamus or down as the rubrospinal tract.
15:15
Cool. What else goes through the posterior limb. The visual fibers.
15:19
So remember, Within the retina of your eyes, you have receptors for the 2nd cranial nerve,
15:24
the optic nerve. The optic nerve fibers will go back, and then half of the fibers
15:29
will cross and form the optic chiasm. After that, they will synapse with the Lateral geniculate
15:34
bodies. From the Lateral Geniculate bodies, the fibers will go back to the occipital lobe, where
15:40
you’ll find the primary visual Cortex. When they go to the Cortex, that is when you’re consciously
15:47
aware of the things you see around you. The fibers that go from the lateral geniculate
15:52
body toward the occipital lobe are called the Optic Radiations, and these fibers go through
15:58
the posterior Limb of internal capsule before going to the occipital lobe. So that’s that one.
16:04
Then we have the Auditory Pathway. This pathway starts around the Cochlea of the inner ear,
16:09
which converts sound into nerve signals through the hair cells. From here,
16:14
these nerve signals are sent through the cochlear nerve to the.. cochlear nuclei in Pons. The fibers
16:20
will then cross to the other side and form the trapezoid body of pons. Then they’ll ascend as the
16:27
lateral lemniscus to the inferior colliculi. Then through the brachium of the inferior colliculus,
16:32
the axons will reach the medial geniculate body and then reach the primary auditory Cortex,
16:38
which is located at the superior temporal gyrus. And the fibers between the medial
16:43
geniculate bodies and the primary auditory Cortex are also going to go through the posterior limb
16:49
of the internal capsule. And they’re called the auditory radiations. So that was all the tracts
16:54
for the Posterior Limb of the internal capsule. Just remember that the internal capsule is the
16:59
control point that all cortical fibers have to go through in order to go from or to the
17:04
cerebral Cortex. And all of these tracts are what we call projection fibers. Awesome.
Deep Gray Matter: Basal Ganglia
17:09
So now we’re gone through the cerebral white matter, which are the association fibers,
17:14
commissural fibers, and projection fibers. The last thing we need to talk about in this
17:19
video is the deep grey matter of the Cerebral Cortex. And these are the Basal Ganglia.
17:25
The basal ganglia are structures that work together in order to help the voluntary movements.
17:31
So let’s go through all the structures that are considered a part of the basal ganglia.
17:34
These are the Caudate Nucleus, Putamen, and Globus Palidus externus and internus. These 4 structures
17:41
are considered the main input and output nuclei of the basal ganglia, they’re called Principal
17:46
Nuclei, all of them. And sometimes you see the word Striatum. So when you combine the Caudate
17:52
nucleus and the Putamen, you get the striatum. And when you combine Putamen and the Globus Pallidus,
17:58
you get the Lentiform Nucleus. Then there are other structures
18:02
that are functionally connected with the basal ganglia. These are the Thalamus,
18:06
or specifically the Ventral anterior and the Ventral Lateral Nucleus of the Thalamus, the
18:11
subthalamic nucleus, and substantia nigra. Then another structure that is part of the
18:16
Basal ganglia, that is closely connected with the cerebral Cortex is Claustrum.
18:21
Now. If we look at a side view of the brain again and highlight the Fornix and the Hippocampus. At
18:27
the end of the Hippocampus, you’ll find the amygdaloid body. This is a structure
18:31
of the limbic system but is associated with the Basal ganglia as well. So now let’s go through
18:37
the structures of the basal ganglia that are associated with the cerebral hemispheres. These
18:42
are the Caudate nucleus, Putamen, Globus Pallidus, Claustrum, Amygdaloid Body. But before doing that,
18:49
we need to have kind fo a basic understanding of what the overall function of the Basal Ganglia is.
18:54
The basic motor function is coordinated by the cerebral Cortex,
18:58
right? Primarily the primary motor area. Whenever you decide to consciously move a limb,
19:04
your primary motor cortex will send motor tracts along the spinal cord to engage muscles necessary
19:10
to do so through the corticospinal tract. But in order for this motor plan to be able
19:15
to go to the muscles, you need to kind of have communication with the basal ganglion.
19:20
SO imagine for a second we’ve combined all the basal ganglia structures into a
19:24
purple bulb here. So the primary motor area has to communicate its motor plan with the basal ganglia.
19:31
The basal ganglia take that motor plan and modify it in a particular way through the
19:36
direct and indirect pathway, and send it back to the cerebral Cortex to send now the proper
19:42
motor plan to either start movement, stop movement or modulate the movement. Beautiful.
19:48
Now. If we remove one of the cerebral hemispheres, except the basal ganglia. And look at them
19:54
all from this perspective. We’ll see this. So what we see here is the Cingulate Gyrus,
20:00
which has the cingulum association fibers for the Limbic System. We see the Corpus callosum, which
20:05
is a part of the commissural fibers. We see septum pellucidum. We can see the Hippocampus, which
20:10
is associated with learning and memory. And it’s connected with the Fornix. Then we see the Caudate
Lobes and Gyri on Inferior Surface
20:16
Nucleus, which has this weird shape of a worm, and it’s connected with the Putamen. So let’s go ahead
20:21
and focus on the anatomy of the caudate nucleus a little bit. The caudate nucleus consists of a
20:26
thick head going towards the frontal lobe. It has a body or corpus within the parietal lobe.
20:33
And it goes back as the tail. And as you see here, the caudate nucleus connects with the Putamen.
20:39
So if we look at them both from an anterior view, we’ll see this.
20:43
So the caudate nucleus is here. The putamen is here, and medially we’ll see the globus pallidus
20:49
exterus and the globus pallidus internus. Medially to the globus pallidus internus,
Insular Lobe
20:54
you can see the Thalamus. So if we go back to this
20:57
picture. Now the locations of these basal ganglia structures kinda make sense, right?
21:02
Now lateral to the Putamen, you’ll find Claustrum. And claustrum is a strip of grey matter,
21:08
situated between the Putamen and the Insular lobe of the brain. The function of the claustrum is
21:14
that it connects the basal ganglion to different cortical areas of the brain.
21:19
Alright, so that was everything I wanted to talk about in terms of the cerebral white
21:23
matter and the deep grey matter. I really hope that was helpful. If
21:27
it was, please like, comment, say hi, and good luck with any upcoming tests if you have that.