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Introduction
0:01
What’s up.
0:03
Meditay here.
0:05
Let’s continue the anatomy of the Central Nervous System.
0:08
In this segment, we’ll cover the complete anatomy of the different parts of the Diencephalon.
0:13
So the central nervous system consists of two parts: the encephalon and the spinal cord.
0:18
The encephalon is then further divided into specific parts.
0:22
We have the brainstem, which consists of the medulla, pons, and the Midbrain or the mesencephalon.
0:27
We have the cerebellum back here, then the Diencephalon and the telencephalon.
0:31
Our focus in this video is going to be the Diencephalon, which is here.
0:35
So in this video, we’re first going to look at the topography of the Diencephalon.
0:39
Basically, understand where is it?
0:42
What parts are considered the Diencephalon?
0:44
And what’s the orientation between these parts?
0:46
After that, we will cover the actual anatomy of all the structures that make up the Diencephalon.
0:51
But let’s orientate and understand their relationship first before doing so.
Topography of Diencephalon
0:57
Alright.
0:58
Here you see Pons, Medulla, Cerebellum, and the Spinal Cord.
1:02
And if we remove one side of the hemisphere, we’ll be able to see the Midbrain.
1:07
And right above the Midbrain, we have our Diencephalon.
1:10
So the Diencephalon is a group of nerve nuclei that surrounds the Third Ventricle.
1:15
SO let’s repeat the ventricular system a little bit.
1:18
I’m sure you remember the fourth Ventricle, which continues down as the central canal.
1:22
And continues upwards as the aqueduct of the Midbrain, which leads into the 3rd Ventricle.
1:27
So again the Diencephalon surrounds the 3rd Ventricle.
1:31
And above the third Ventricle, on either side, we have the lateral ventricles.
1:35
Alright.
1:36
So the Diencephalon surrounds the third Ventricle, and its job is to connect different parts
1:42
of the telencephalon, with the brainstem.
1:45
It’s like the post office of our brain, directing the signals to the right place.
1:50
So let’s now remove the surrounding structures that are not significant to us yet, and orientate
1:55
around the different parts of the Diencephalon.
Parts of the Diencephalon
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So the Diencephalon consists of 5 parts.
2:01
And that includes the Thalamus, Epithalamus, Subthalamus, Metathalamus, and Hypothalamus.
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Now I’ve made an orientation scheme that really helped me orientate around the Diencephalon
2:12
when I started studying it.
2:14
So we can start off here, looking at the Medulla, Pons, Midbrain and Cerebellum.
2:18
Now.
2:19
Let’s say this is you, right?
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A cute little figure swimming around the Cerebrospinal fluid within the fourth Ventricle.
2:26
Now we’re going to send you off for some adventure.
2:30
So you swim upwards, up through the aqueduct of the Midbrain, until you get to the 3rd
2:35
Ventricle.
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From your standpoint right now.
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When you look to your right and to your left.
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You’ll see the Thalamus on either side of the third Ventricle.
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So if we go back to our list, Thalamus is our first stop, so let’s go ahead and put
2:48
a checkmark there.
2:49
Now, you decide to turn around and swim to the very back of the 3rd Ventricle, where
2:55
you’ll notice a small pouch handing on the back here like a tail, called the Pineal Gland.
3:00
And the Pineal Gland is attached on the backside here through the Habenula.
3:04
All of these together form the Epithalamus.
3:07
So let’s go ahead and put a checkmark here as well.
3:10
Next now, if you duck, kind of look inferiorly to the Thalamus, you’ll find the Subthalamus.
3:16
This is another important component of the Diencephalon.
3:19
Then on the lateral sides of each thalamus, you’ll find two nuclei called the medial
3:24
geniculate body and the lateral geniculate body.
3:28
These two nuclei are termed Metathlamus, which is another significant part of the Diencephalon.
3:33
Now, you decide to turn around and swim forward, to explore what’s on the anterior side.
3:39
And what you see is surprising.
3:41
You’ll see grey matter surrounding the anterior portion of the 3rd Ventricle, which is termed
3:46
Hypothalamus.
3:47
And the Hypothalamus is going to be more of an area that structures are going to be a
3:52
part of.
3:53
Like the mamillary bodies.
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Then there are a bunch of hypothalamic nuclei around this area.
3:59
Some of these nuclei, have axons going down as tuber cinetum, which form a stalk called
4:04
the infundibulum that connects to the posterior part of the pituitary gland.
4:09
Also called neurohypophysis, since it contains neural fibers.
4:13
The anterior part of the pituitary gland is not considered a part of the Hypothalamus
4:17
since it’s glandular.
4:19
It has a different origin during development.
4:22
Other parts that are considered a part of the Hypothalamus are the optic chiasm and
4:26
the optic tract.
4:27
Some sources say they’re their own part of the Diencephalon, called thalamus opticus,
4:32
and some sources include them as a part of the Hypothalamus.
4:36
In this video we’ll count them as a aprt fo the Hypothalamus, but you know keep that
4:39
in mind.
4:40
So all of these structures are going to be a part of the Hypothalamus.
4:44
Now.
4:45
Let’s work our way down the list, starting with the Thalamus.
Thalamus: External
4:49
So I think the best way to learn its anatomy is to go through all the structures one by
4:54
one, starting with the external features and then the internal ones.
4:57
So the Thalamus is here in green.
4:59
And if we look at it from a posterior perspective, you’ll see the thalami on either side right
5:04
here.
5:05
The most anterior part of each thalami forms a tubercle shape.
5:09
We call it the Anterior tubercle.
5:11
And the poster end is a more rounded part is called Pulvinar.
5:16
And in between the Right and left Thalami, there’s a connection point called Interthalamic
5:21
adhesion that connects both thalami together.
5:24
So those are the only external features I’m gonna tell you to remember: anterior tubercle,
5:29
Pulvinar, and the Interthlamic Adhesion.
Thalamus: Internal
5:32
Now let’s slice the Thalamus and look at it from a superior perspective.
5:36
We’ll see this.
5:38
Ok.
5:39
This is a thalamus.
5:40
The Thalamus is an egg-shaped structure.
5:43
And it’s divided into three different kinds of nuclear groups by this little Y-shaped
5:48
structure.
5:49
This Y shaped structure, is called the Internal Medullary Lamina.
5:52
Sometimes it can be referred to as the Medial Medullary Lamina.
5:55
The nice thing about this internal medullary lamina is that it’s actually a white matter
6:00
structure.
6:01
The second thing that’s really cool is that it separates the Thalamus into three different
6:06
groups.
6:07
The first one that we’re gonna talk about, is the anterior group of nuclei, within the
6:10
anterior tubercle.
6:12
Then we have the medial group of nuclei, and the lateral group of nuclei.
6:16
Alright, now the Thalamus is actually.
6:19
You know, when you learning about it it can be quite daunting.
6:21
Especially when you look in the books they got all these nuclei and you’re like ‘’What
6:25
the crap is going on?’’.
6:26
I’ll only focus on the very basic neuroanatomy of it so that you kinda have a good ground
6:31
base in understanding the Thalamus.
6:33
So let’s do the anterior nuclei first.
6:36
The anterior nuclei is a part of a circuit responsible for emotional episodic memory.
6:42
Now, what doe that mean?
6:44
That means, your ability to recall and mentally re-experience specific episodes from one’s
6:50
personal past.
6:51
So this is the one that keeps you awake at night when you’re brain goes wandering off
6:54
about awkward situations you’ve been in.
6:57
And it can do that because it’s a part of what is called the Limbic System.
7:01
We’ll talk about the limbic system in detail when we go through the internal structures
7:05
of the hemispheres, but the Limbic system is initially responsible for the control of
7:09
emotions, behaviors, motivation, and memory.
7:13
And it’s a system that consists of several parts.
7:16
And the ones that are involved with the anterior group of nuclei are, you know, the Thalamus
7:21
itself, the Hypothalamus.
7:23
The Amygdala, Hypocampus, the cingulate gyrus, and the fornix.
7:27
So all of these structures are involved with the anterior nuclei of the Thalamus.
7:32
Let’s see how.
7:33
So the Mamillary body, which is a part of the Hypothalamus.
7:36
Send fibers to our anterior thalamic nuclei.
7:40
From the anterior thalamic nuclei, they send their axons to the cingulate gyrus.
7:45
The cingulate gyrus then sends axons downwards, and they eventually reach the Hippocampus.
7:50
Then, from the hippocampus, fibers go through the fornix and then finish the circuit in
7:55
the mamilly body again.
7:57
This whole circuit is called the papez circuit.
8:00
And this is the circuit that give you the ability to recall and reexperience past memory,
8:05
for emotional episodic memory.
8:08
Next, we have the medial group nuclei.
8:12
Or also called the medial dorsal nuclei.
8:15
And what these nuclei do is that they relate the sensory input, motor input, and olfactory
8:21
input with emotions.
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Meaning gives you the emotional aspect of smell or any sensory or motor input.
8:28
And it’s able to do that because it receives its fibers from the olfactory Cortex, which
8:33
is the area that perceives smell.
8:36
It also receives input from the Amygdala, which is involved in fear, anxiety, aggression,
8:41
and all of those kind of emotions.
8:43
So it will send its input to the medial dorsal nucleus.
8:46
And then there’s the Hypothalamus.
8:48
So all of these send their axons to the lateral thalamic nucleus.
8:53
And once the medial dorsal nucleus receives all the emotions, it sends that information
8:58
to the prefrontal cortex, which is an area responsible for attention, personality, abstract
9:03
thinking, and all of those things.
9:05
Cool, so that’s the medial dorsal nucleus.
9:09
Now let’s do the lateral group of nuclei The Lateral group of nuclei is divided into
9:14
a lateral Dorsal row, and a lateral Ventral row.
9:18
And all the way on the back here, we have our Pulvinar.
9:21
The lateral Dorsal row is divided into two portions.
9:24
It’s divided into the Lateral Dorsal nuclei, and the Lateral Posterior nuclei.
9:30
The Lateral dorsal, lateral posterior and the pulvinar are mostly involved in visual
9:35
and auditory senses, I’ll show you in a bit when we talk about the medial geniculate
9:39
body and the lateral geniculate body, so we’ll put these on hold a little bit.
9:43
So let’s talk about the Lateral Ventral row.
9:46
This is actually the most important part of the Thalamus.
9:49
And it consist of the ventral Anterior and the ventral Lateral.
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These two nuclei are a part of the basal ganglia.
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Remember the basal ganglia are also subcortical grey matter, but they’re responsible for
10:02
coordinating, starting and stopping voluntary movements.
10:05
They include the Caudate nucleus, Putamen, Globus pallidus exterus, and internus.
10:11
Thalamus, but not the whole Thalamus.
10:13
Only the ventral anterior and the ventral lateral group of nuclei are gonna be a part
10:17
of the basal ganglia.
10:19
That is why they’re special.
10:20
The last ones are the subthalamic nuclei and the substantia nigra of the Midbrain.
10:25
So if we take all the structures of the basal ganglia and group them all together.
10:30
We’ll see that the Ventral anterior and the ventral lateral nuclei are also going
10:35
to be responsible for initiation and planning of movement.
10:39
And it does that by the Basal ganglia structures receiving impulses from the primary motor
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cortex.
10:45
Impulses within the basal ganglion are going to go through the ventral anterior and the
10:50
ventral lateral nuclei, which are then going to end up back towards the primary motor cortex,
10:55
for a better planning and initiation of the movement
10:58
Another thing that is kinda special for the ventral lateral, in addition to the basal
11:02
ganglia is, you know the cerebellum?
11:05
The cerebellum is involved in receiving information about proprioception.
11:10
Meaning it receives information about the position of your muscles your tendons, you
11:13
joints, your ligaments.
11:15
It’s receiving all of that information through the spinocerebellar tract and the external
11:20
arcuate fibers.
11:22
It also receives information from the inner ear.
11:24
You know the vestibular system?
11:26
Which is involved in balance?
11:27
The cerebellum receives information from the inner ear through the vestibulocerebellar
11:32
tract, based upon our equilibrium.
11:35
It also receives a pre-planned motor plan, through the corticopontocerebellar tract,
11:41
which remember either goes to the red nucleus and then down as the rubrospinal tract, or
11:46
it ascends back up through the Thalamus, or specifically the ventral lateral nucleus.
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SO the cerebellum receives all of that information.
11:54
Our balance, or proprioception, the motor plan and all of those things.
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And then it sends it to the Thalamus and then the signals are sent up to the Cortex.
12:04
What area of the cerebral Cortex you say?
12:06
The primary motor cortex.
12:08
This is a very cool and controlled process.
12:10
All of this just to move a finger or a limb.
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The last two nuclei are the ventro-posterio-Lateral nucleus, or abbreviated as VPL.
12:19
It receives sensory information for the Trunk and Limb, through a tract that you’re probably
12:24
familiar with by now.
12:26
That tract originates from the Gracile fascicle and the Cuneate Fascicle.
12:30
They are responsible for epicritic sensibility, proprioception, and mechanoreceptors like
12:35
touch and vibration.
12:37
They will ascend as the medial lemniscus and then go to the VPL nucleus to be directed
12:42
towards the primary somatosensory Cortex.
12:45
Another tract it receives input from is the spinothalamic tract.
12:49
And remember this tract is responsible for sensation in regards to Pain, Temperature,
12:54
Pressure, and Touch.
12:56
The spinothalamic tract goes to the VTL, and then up to the somatosensory Cortex.
13:01
So that is the ventroposteriolateral nuclei.
13:05
The other nucleus is the ventroposteriomedial nucleus.
13:09
Or abbreviated as the VPM.
13:11
These nuclei are also sensory nuclei, and they receive sensory information from the
13:16
Face, as well as Gustation, or sense of taste.
13:20
It receives its senses from the Trigeminal nerve, through the trigeminal lemniscus about
13:25
proprioception, pain, touch, all of those things in the facial region.
13:30
So that is this one.
13:31
The other one is Gustation, or taste.
13:34
You know there are specific cranial nerves responsible for the sense of taste.
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These are the facial, glossopharyngeal, and the vagus nerve.
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All of them will go the VPM.
13:44
And then from the VentroPosterioMedial Nuclei, They will give off axons towards the…
13:51
Primary sensory cortex.
13:52
Awesome.
13:53
Now we’re done with the Thalamus.
Metathalamus
13:56
From this view.
13:57
We can talk about the metathalamus.
13:59
Which remember are the Medial geniculate body, and the Lateral geniculate body.
14:03
The Medial Geniculate body is associated with hearing.
14:07
So it’s a part of the…
14:08
Auditory Pathway.
14:10
This pathway starts around the cochlea of the inner ear, which converts hearing into
14:14
nerve signals through the hair cells.
14:17
From here, these nerve signals are sent through the cochlear nerve to the.. cochlear nuclei
14:23
in Pons.
14:24
The cochlear nuclei will then cross to the other side and form the trapezoid body of
14:29
pons, and then ascend as the lateral lemniscus, to the inferior colliculi.
14:35
Then through the brachium of the inferior coliculus, the axons will reach the medial
14:40
geniculate body, and then reach the primary auditory Cortex, which is located at the superior
14:45
temporal gyrus.
14:47
So that is the Medial Geniculate Body.
14:50
The lateral geniculate body is related to vision.
14:53
So it’s associated with the visual pathway.
14:55
So remember, Within the retina of your eyes, you have receptors for the 2nd cranial nerve,
15:00
the optic nerve.
15:01
The fibers of the optic nerve will go back, and then half of the fibers will cross and
15:07
form the optic chiasm.
15:09
After that, they will synapse with the Lateral geniculate bodies, and From the Lateral Geniculate
15:14
bodies, the fibers will go back to the occipital lobe, which is where you’ll find the primary
15:19
visual Cortex.
15:20
When they go to the Cortex, that is when you’re consciously aware of the things you see around
15:27
you.
15:28
But fibers also go from the lateral geniculate bodies to the superior colliculi through the
15:33
Brachium of the superior colliculi.
15:36
The superior colliculi are responsible for a coordinated movement of the eyes and neck,
15:40
and it’s able to do that through the tectospinal tract, which sends motor impulses for the
15:46
eyes and the neck muscles.
15:48
So the superior and the inferior colliculus is responsible for Reflexive movement of the
15:53
head and neck through visual and hearing stimulus.
Metathalamus Connections with Thalamus
15:57
Now.
15:58
Remember we talked about the pulvinar and the lateral posterior and the lateral dorsal
16:02
nucleus?
16:03
They’re actually involved in all of these things.
16:06
But the Pulvinar especially, will receive fibers from the medial geniculate body about
16:11
hearing, Lateral geniculate body about vision, as well as superior colliculus for reflexive
16:16
movement of the head through visual stimulus, and inferior colliculus for reflexive movement
16:21
of the head through auditory stimulus.
16:24
All of those go-to Pulvinar, and the pulvinar sends the information primarily to the tertiary
16:30
areas in the brain, which gives you the possibility to take past experiences, let’s say someone’s
16:35
face, or maybe even a flower or a facial expression.
16:39
And it helps with recognition.
16:40
It gives meaning to the image you’re seeing.
16:43
That is what the Pulvinar is responsible for.
16:45
Talking all of that information and sending them to the association areas, or the tertiary
16:51
and secondary areas of the brain.
16:53
So that was the metathalamus, boom.
16:55
Let’s move on.
Epithalamus
16:57
The next one on our list is the Epithalamus.
17:00
So let’s go back to this image.
17:02
We’re already familiar with the Thalamus now.
17:05
But on the posterior side, we can see the Epithalamus right here.
17:09
The Epithalamus is a veery small area, and it consists of mainly the pineal gland.
17:15
And the pineal gland mainly produces one of the most important hormones in our body, and
17:21
that is the hormone that makes u sleep, called melatonin.
17:24
So essentially, it regulates the sleep-wake cycle.
17:28
The Pineal gland is attached to the posterior part of the Thalamus.
17:32
On either side of the pineal gland, you’ll see a triangular-like structure called the
17:37
Habenular Trigone, which is white matter that contains some habenular nuclei which are considered
17:42
to be a part of the limbic system.
17:44
Between the habenular triangle, we’ll find the habenular commissure, which connects both
17:49
habenular trigones together.
17:52
And you’ll also find the posterior commissure here as well.
17:55
So that is the Epithalamus.
Subthalamus
17:57
Next, let’s do the Subthalamus.
17:59
They’re called Sub-thalamus, so under the Thalamus.
18:03
So here is the Thalamus.
18:04
Here is the Subthalamus.
18:06
Or the subthalamic Nuclei.
18:07
And the Subthalamus is essentially a part of the basal ganglion.
18:11
SO all the other structures of the basal ganglion will work together with the Subthalamus to
18:17
help start a movement, stop movement and coordinate voluntary movement.
18:22
So that is all I had for the anatomy of the Subthalamus.
Hypothalamus
18:25
Let’s now do the last part of the diencephalon, which is the structure you’ll find around
18:29
the anterior portion of the third Ventricle, called the Hypothalamus.
18:34
Really what I want you more to understand rather than going detailed into the neuroanatomy
18:38
is to know that the Hypothalamus is more of an area that is made up of different parts.
18:44
Or different nuclei.
18:45
And it has some external parts that are considered a part of the Hypothalamus.
18:50
Remember the optic pathway has the optic chiasm and the optic tracts.
18:55
Both of these are consideres a part of the Hypothalamus.
18:58
As mentioned earlier, some sources mention these as a separate part of Diencephalon as
19:02
Thalamus Opticus, but here we’ll include them as a part of the Hypothalamus.
19:07
So, if you look at the Diencephalon, from an anterior perspective, we’ll see the Hypothalamus
19:12
here in red, and the Optic chiasm and the optic tract right here.
19:17
Awesome.
19:18
Now, the other part of the Hypothalamus is going to be the Mammillary body.
19:22
And they’re responsible for Emotional Episodic memory as mentioned earlier.
19:26
As well as reflexes associated with olfaction.
19:29
Remember earlier when we went through the papez circuit associated with the anterior
19:33
nuclei of the Thalamus?
19:35
Where do we have the Thalamus, Hypothalamus, Amygdala, Hippocampus, cingulate gyrus, and
19:40
fornix?
19:41
The mammillary body will send axons to the anterior nuclei of the Thalamus.
19:46
Which will send its fibers to the cingulate gyrus, and then to the hippocampal area, then
19:51
to the fornix, and back to the mammillary body.
19:53
This circuit will be responsible for emotional episodic memory, which is the emotional reaction
19:59
to a past memory.
20:01
So that was the mamillary bodies.
20:04
Other things we’ll find in the Hypothalamus are these Hypothalamic nuclei.
20:08
There are many nuclei in the Hypothalamus.
20:11
Some of them send down their axons through the tuber cinerum, which will get tighter
20:16
and form a stalk called the infundibulum, which will then synapse with nuclei in the
20:21
posterior pituitary gland.
Hypothalamic Nuclei
20:23
So hormones released from the posterior pituitary gland, like vasopressin or Oxytocin, get their
20:29
trigger stimulus from the Hypothalamus through these fibers.
20:33
Those are the major structures of the Hypothalamus.
20:36
If you wanna go deeper into the neurology of it.
20:39
We can look at a side view of the Hypothalamus and really look at all the hypothalamic nuclei.
20:43
They’re arranged into areas.
20:46
Like the lateral hypothalamic area, the posterior hypothalamic area, and the anterior hypothalamic
20:51
area.
20:52
These nuclei are responsible for different things.
20:55
The paraventricular nuclei are associated with pain for example.
20:59
The preoptic nucleus decreases the heart rate and the blood pressure and many other things.
21:04
We got the Suprachiasmatic nucleus which is a part of the circadian rhythm, the sleep-wake
21:09
cycle, Supraoptic nucleus for thirst, Arcuate nucleus which regulates the release of many
21:15
hormones.
21:16
The ventromedial nucleus for the satiety feeling, this nucleus doesn’t work in my body.
21:21
I’m always hungry.
21:22
Then we got our mammillary body here.
21:24
The dorsomedial nucleus for sleep regulation and food intake.
21:28
You might wanna go into detail into this when you study the physiology or neurology.
21:33
But for now.
21:34
That was the anatomy of the Diencephalon and I hope that was helpful.
21:35
Please put a like, comment, share, whatever you find convenient to you.
21:36
Our next video will be about the Telencephalon.
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