Diencephalon Anatomy (Thalamus, Epithalamus, Subthalamus, Metathalamus, Hypothalamus)

What’s up. Meditay here. Let’s continue the anatomy of the Central

Nervous System. In this segment, we’ll cover the complete

anatomy of the different parts of the Diencephalon. So the central nervous system consists of

two parts: the encephalon and the spinal cord. The encephalon is then further divided into

specific parts. We have the brainstem, which consists of the

medulla, pons, and the Midbrain or the mesencephalon. We have the cerebellum back here, then the

Diencephalon and the telencephalon. Our focus in this video is going to be the

Diencephalon, which is here. So in this video, we’re first going to look

at the topography of the Diencephalon. Basically, understand where is it? What parts are considered the Diencephalon? And what’s the orientation between these

parts? After that, we will cover the actual anatomy

of all the structures that make up the Diencephalon. But let’s orientate and understand their

relationship first before doing so. Alright. Here you see Pons, Medulla, Cerebellum, and

the Spinal Cord. And if we remove one side of the hemisphere,

we’ll be able to see the Midbrain. And right above the Midbrain, we have our

Diencephalon. So the Diencephalon is a group of nerve nuclei

that surrounds the Third Ventricle. SO let’s repeat the ventricular system a

little bit. I’m sure you remember the fourth Ventricle,

which continues down as the central canal. And continues upwards as the aqueduct of the

Midbrain, which leads into the 3rd Ventricle. So again the Diencephalon surrounds the 3rd

Ventricle. And above the third Ventricle, on either side,

we have the lateral ventricles. Alright. So the Diencephalon surrounds the third Ventricle,

and its job is to connect different parts of the telencephalon, with the brainstem. It’s like the post office of our brain,

directing the signals to the right place. So let’s now remove the surrounding structures

that are not significant to us yet, and orientate around the different parts of the Diencephalon. So the Diencephalon consists of 5 parts. And that includes the Thalamus, Epithalamus,

Subthalamus, Metathalamus, and Hypothalamus. Now I’ve made an orientation scheme that

really helped me orientate around the Diencephalon when I started studying it. So we can start off here, looking at the Medulla,

Pons, Midbrain and Cerebellum. Now. Let’s say this is you, right? A cute little figure swimming around the Cerebrospinal

fluid within the fourth Ventricle. Now we’re going to send you off for some

adventure. So you swim upwards, up through the aqueduct

of the Midbrain, until you get to the 3rd Ventricle. From your standpoint right now. When you look to your right and to your left. You’ll see the Thalamus on either side of

the third Ventricle. So if we go back to our list, Thalamus is

our first stop, so let’s go ahead and put a checkmark there. Now, you decide to turn around and swim to

the very back of the 3rd Ventricle, where you’ll notice a small pouch handing on the

back here like a tail, called the Pineal Gland. And the Pineal Gland is attached on the backside

here through the Habenula. All of these together form the Epithalamus. So let’s go ahead and put a checkmark here

as well. Next now, if you duck, kind of look inferiorly

to the Thalamus, you’ll find the Subthalamus. This is another important component of the

Diencephalon. Then on the lateral sides of each thalamus,

you’ll find two nuclei called the medial geniculate body and the lateral geniculate

body. These two nuclei are termed Metathlamus, which

is another significant part of the Diencephalon. Now, you decide to turn around and swim forward,

to explore what’s on the anterior side. And what you see is surprising. You’ll see grey matter surrounding the anterior

portion of the 3rd Ventricle, which is termed Hypothalamus. And the Hypothalamus is going to be more of

an area that structures are going to be a part of. Like the mamillary bodies. Then there are a bunch of hypothalamic nuclei

around this area. Some of these nuclei, have axons going down

as tuber cinetum, which form a stalk called the infundibulum that connects to the posterior

part of the pituitary gland. Also called neurohypophysis, since it contains

neural fibers. The anterior part of the pituitary gland is

not considered a part of the Hypothalamus since it’s glandular. It has a different origin during development. Other parts that are considered a part of

the Hypothalamus are the optic chiasm and the optic tract. Some sources say they’re their own part

of the Diencephalon, called thalamus opticus, and some sources include them as a part of

the Hypothalamus. In this video we’ll count them as a aprt

fo the Hypothalamus, but you know keep that in mind. So all of these structures are going to be

a part of the Hypothalamus. Now. Let’s work our way down the list, starting

with the Thalamus. So I think the best way to learn its anatomy

is to go through all the structures one by one, starting with the external features and

then the internal ones. So the Thalamus is here in green. And if we look at it from a posterior perspective,

you’ll see the thalami on either side right here. The most anterior part of each thalami forms

a tubercle shape. We call it the Anterior tubercle. And the poster end is a more rounded part

is called Pulvinar. And in between the Right and left Thalami,

there’s a connection point called Interthalamic adhesion that connects both thalami together. So those are the only external features I’m

gonna tell you to remember: anterior tubercle, Pulvinar, and the Interthlamic Adhesion. Now let’s slice the Thalamus and look at

it from a superior perspective. We’ll see this. Ok. This is a thalamus. The Thalamus is an egg-shaped structure. And it’s divided into three different kinds

of nuclear groups by this little Y-shaped structure. This Y shaped structure, is called the Internal

Medullary Lamina. Sometimes it can be referred to as the Medial

Medullary Lamina. The nice thing about this internal medullary

lamina is that it’s actually a white matter structure. The second thing that’s really cool is that

it separates the Thalamus into three different groups. The first one that we’re gonna talk about,

is the anterior group of nuclei, within the anterior tubercle. Then we have the medial group of nuclei, and

the lateral group of nuclei. Alright, now the Thalamus is actually. You know, when you learning about it it can

be quite daunting. Especially when you look in the books they

got all these nuclei and you’re like ‘’What the crap is going on?’’. I’ll only focus on the very basic neuroanatomy

of it so that you kinda have a good ground base in understanding the Thalamus. So let’s do the anterior nuclei first. The anterior nuclei is a part of a circuit

responsible for emotional episodic memory. Now, what doe that mean? That means, your ability to recall and mentally

re-experience specific episodes from one’s personal past. So this is the one that keeps you awake at

night when you’re brain goes wandering off about awkward situations you’ve been in. And it can do that because it’s a part of

what is called the Limbic System. We’ll talk about the limbic system in detail

when we go through the internal structures of the hemispheres, but the Limbic system

is initially responsible for the control of emotions, behaviors, motivation, and memory. And it’s a system that consists of several

parts. And the ones that are involved with the anterior

group of nuclei are, you know, the Thalamus itself, the Hypothalamus. The Amygdala, Hypocampus, the cingulate gyrus,

and the fornix. So all of these structures are involved with

the anterior nuclei of the Thalamus. Let’s see how. So the Mamillary body, which is a part of

the Hypothalamus. Send fibers to our anterior thalamic nuclei. From the anterior thalamic nuclei, they send

their axons to the cingulate gyrus. The cingulate gyrus then sends axons downwards,

and they eventually reach the Hippocampus. Then, from the hippocampus, fibers go through

the fornix and then finish the circuit in the mamilly body again. This whole circuit is called the papez circuit. And this is the circuit that give you the

ability to recall and reexperience past memory, for emotional episodic memory. Next, we have the medial group nuclei. Or also called the medial dorsal nuclei. And what these nuclei do is that they relate

the sensory input, motor input, and olfactory input with emotions. Meaning gives you the emotional aspect of

smell or any sensory or motor input. And it’s able to do that because it receives

its fibers from the olfactory Cortex, which is the area that perceives smell. It also receives input from the Amygdala,

which is involved in fear, anxiety, aggression, and all of those kind of emotions. So it will send its input to the medial dorsal

nucleus. And then there’s the Hypothalamus. So all of these send their axons to the lateral

thalamic nucleus. And once the medial dorsal nucleus receives

all the emotions, it sends that information to the prefrontal cortex, which is an area

responsible for attention, personality, abstract thinking, and all of those things. Cool, so that’s the medial dorsal nucleus. Now let’s do the lateral group of nuclei

The Lateral group of nuclei is divided into a lateral Dorsal row, and a lateral Ventral

row. And all the way on the back here, we have

our Pulvinar. The lateral Dorsal row is divided into two

portions. It’s divided into the Lateral Dorsal nuclei,

and the Lateral Posterior nuclei. The Lateral dorsal, lateral posterior and

the pulvinar are mostly involved in visual and auditory senses, I’ll show you in a

bit when we talk about the medial geniculate body and the lateral geniculate body, so we’ll

put these on hold a little bit. So let’s talk about the Lateral Ventral

row. This is actually the most important part of

the Thalamus. And it consist of the ventral Anterior and

the ventral Lateral. These two nuclei are a part of the basal ganglia. Remember the basal ganglia are also subcortical

grey matter, but they’re responsible for coordinating, starting and stopping voluntary

movements. They include the Caudate nucleus, Putamen,

Globus pallidus exterus, and internus. Thalamus, but not the whole Thalamus. Only the ventral anterior and the ventral

lateral group of nuclei are gonna be a part of the basal ganglia. That is why they’re special. The last ones are the subthalamic nuclei and

the substantia nigra of the Midbrain. So if we take all the structures of the basal

ganglia and group them all together. We’ll see that the Ventral anterior and

the ventral lateral nuclei are also going to be responsible for initiation and planning

of movement. And it does that by the Basal ganglia structures

receiving impulses from the primary motor cortex. Impulses within the basal ganglion are going

to go through the ventral anterior and the ventral lateral nuclei, which are then going

to end up back towards the primary motor cortex, for a better planning and initiation of the

movement Another thing that is kinda special for the

ventral lateral, in addition to the basal ganglia is, you know the cerebellum? The cerebellum is involved in receiving information

about proprioception. Meaning it receives information about the

position of your muscles your tendons, you joints, your ligaments. It’s receiving all of that information through

the spinocerebellar tract and the external arcuate fibers. It also receives information from the inner

ear. You know the vestibular system? Which is involved in balance? The cerebellum receives information from the

inner ear through the vestibulocerebellar tract, based upon our equilibrium. It also receives a pre-planned motor plan,

through the corticopontocerebellar tract, which remember either goes to the red nucleus

and then down as the rubrospinal tract, or it ascends back up through the Thalamus, or

specifically the ventral lateral nucleus. SO the cerebellum receives all of that information. Our balance, or proprioception, the motor

plan and all of those things. And then it sends it to the Thalamus and then

the signals are sent up to the Cortex. What area of the cerebral Cortex you say? The primary motor cortex. This is a very cool and controlled process. All of this just to move a finger or a limb. The last two nuclei are the ventro-posterio-Lateral

nucleus, or abbreviated as VPL. It receives sensory information for the Trunk

and Limb, through a tract that you’re probably familiar with by now. That tract originates from the Gracile fascicle

and the Cuneate Fascicle. They are responsible for epicritic sensibility,

proprioception, and mechanoreceptors like touch and vibration. They will ascend as the medial lemniscus and

then go to the VPL nucleus to be directed towards the primary somatosensory Cortex. Another tract it receives input from is the

spinothalamic tract. And remember this tract is responsible for

sensation in regards to Pain, Temperature, Pressure, and Touch. The spinothalamic tract goes to the VTL, and

then up to the somatosensory Cortex. So that is the ventroposteriolateral nuclei. The other nucleus is the ventroposteriomedial

nucleus. Or abbreviated as the VPM. These nuclei are also sensory nuclei, and

they receive sensory information from the Face, as well as Gustation, or sense of taste. It receives its senses from the Trigeminal

nerve, through the trigeminal lemniscus about proprioception, pain, touch, all of those

things in the facial region. So that is this one. The other one is Gustation, or taste. You know there are specific cranial nerves

responsible for the sense of taste. These are the facial, glossopharyngeal, and

the vagus nerve. All of them will go the VPM. And then from the VentroPosterioMedial Nuclei,

They will give off axons towards the… Primary sensory cortex. Awesome. Now we’re done with the Thalamus. From this view. We can talk about the metathalamus. Which remember are the Medial geniculate body,

and the Lateral geniculate body. The Medial Geniculate body is associated with

hearing. So it’s a part of the… Auditory Pathway. This pathway starts around the cochlea of

the inner ear, which converts hearing into nerve signals through the hair cells. From here, these nerve signals are sent through

the cochlear nerve to the.. cochlear nuclei in Pons. The cochlear nuclei will then cross to the

other side and form the trapezoid body of pons, and then ascend as the lateral lemniscus,

to the inferior colliculi. Then through the brachium of the inferior

coliculus, the axons will reach the medial geniculate body, and then reach the primary

auditory Cortex, which is located at the superior temporal gyrus. So that is the Medial Geniculate Body. The lateral geniculate body is related to

vision. So it’s associated with the visual pathway. So remember, Within the retina of your eyes,

you have receptors for the 2nd cranial nerve, the optic nerve. The fibers of the optic nerve will go back,

and then half of the fibers will cross and form the optic chiasm. After that, they will synapse with the Lateral

geniculate bodies, and From the Lateral Geniculate bodies, the fibers will go back to the occipital

lobe, which is where you’ll find the primary visual Cortex. When they go to the Cortex, that is when you’re

consciously aware of the things you see around you. But fibers also go from the lateral geniculate

bodies to the superior colliculi through the Brachium of the superior colliculi. The superior colliculi are responsible for

a coordinated movement of the eyes and neck, and it’s able to do that through the tectospinal

tract, which sends motor impulses for the eyes and the neck muscles. So the superior and the inferior colliculus

is responsible for Reflexive movement of the head and neck through visual and hearing stimulus. Now. Remember we talked about the pulvinar and

the lateral posterior and the lateral dorsal nucleus? They’re actually involved in all of these

things. But the Pulvinar especially, will receive

fibers from the medial geniculate body about hearing, Lateral geniculate body about vision,

as well as superior colliculus for reflexive movement of the head through visual stimulus,

and inferior colliculus for reflexive movement of the head through auditory stimulus. All of those go-to Pulvinar, and the pulvinar

sends the information primarily to the tertiary areas in the brain, which gives you the possibility

to take past experiences, let’s say someone's face, or maybe even a flower or a facial expression. And it helps with recognition. It gives meaning to the image you’re seeing. That is what the Pulvinar is responsible for. Talking all of that information and sending

them to the association areas, or the tertiary and secondary areas of the brain. So that was the metathalamus, boom. Let’s move on. The next one on our list is the Epithalamus. So let’s go back to this image. We’re already familiar with the Thalamus

now. But on the posterior side, we can see the

Epithalamus right here. The Epithalamus is a veery small area, and

it consists of mainly the pineal gland. And the pineal gland mainly produces one of

the most important hormones in our body, and that is the hormone that makes u sleep, called

melatonin. So essentially, it regulates the sleep-wake

cycle. The Pineal gland is attached to the posterior

part of the Thalamus. On either side of the pineal gland, you’ll

see a triangular-like structure called the Habenular Trigone, which is white matter that

contains some habenular nuclei which are considered to be a part of the limbic system. Between the habenular triangle, we’ll find

the habenular commissure, which connects both habenular trigones together. And you’ll also find the posterior commissure

here as well. So that is the Epithalamus. Next, let’s do the Subthalamus. They’re called Sub-thalamus, so under the

Thalamus. So here is the Thalamus. Here is the Subthalamus. Or the subthalamic Nuclei. And the Subthalamus is essentially a part

of the basal ganglion. SO all the other structures of the basal ganglion

will work together with the Subthalamus to help start a movement, stop movement and coordinate

voluntary movement. So that is all I had for the anatomy of the

Subthalamus. Let’s now do the last part of the diencephalon,

which is the structure you’ll find around the anterior portion of the third Ventricle,

called the Hypothalamus. Really what I want you more to understand

rather than going detailed into the neuroanatomy is to know that the Hypothalamus is more of

an area that is made up of different parts. Or different nuclei. And it has some external parts that are considered

a part of the Hypothalamus. Remember the optic pathway has the optic chiasm

and the optic tracts. Both of these are consideres a part of the

Hypothalamus. As mentioned earlier, some sources mention

these as a separate part of Diencephalon as Thalamus Opticus, but here we’ll include

them as a part of the Hypothalamus. So, if you look at the Diencephalon, from

an anterior perspective, we’ll see the Hypothalamus here in red, and the Optic chiasm and the

optic tract right here. Awesome. Now, the other part of the Hypothalamus is

going to be the Mammillary body. And they’re responsible for Emotional Episodic

memory as mentioned earlier. As well as reflexes associated with olfaction. Remember earlier when we went through the

papez circuit associated with the anterior nuclei of the Thalamus? Where do we have the Thalamus, Hypothalamus,

Amygdala, Hippocampus, cingulate gyrus, and fornix? The mammillary body will send axons to the

anterior nuclei of the Thalamus. Which will send its fibers to the cingulate

gyrus, and then to the hippocampal area, then to the fornix, and back to the mammillary

body. This circuit will be responsible for emotional

episodic memory, which is the emotional reaction to a past memory. So that was the mamillary bodies. Other things we’ll find in the Hypothalamus

are these Hypothalamic nuclei. There are many nuclei in the Hypothalamus. Some of them send down their axons through

the tuber cinerum, which will get tighter and form a stalk called the infundibulum,

which will then synapse with nuclei in the posterior pituitary gland. So hormones released from the posterior pituitary

gland, like vasopressin or Oxytocin, get their trigger stimulus from the Hypothalamus through

these fibers. Those are the major structures of the Hypothalamus. If you wanna go deeper into the neurology

of it. We can look at a side view of the Hypothalamus

and really look at all the hypothalamic nuclei. They’re arranged into areas. Like the lateral hypothalamic area, the posterior

hypothalamic area, and the anterior hypothalamic area. These nuclei are responsible for different

things. The paraventricular nuclei are associated

with pain for example. The preoptic nucleus decreases the heart rate

and the blood pressure and many other things. We got the Suprachiasmatic nucleus which is

a part of the circadian rhythm, the sleep-wake cycle, Supraoptic nucleus for thirst, Arcuate

nucleus which regulates the release of many hormones. The ventromedial nucleus for the satiety feeling,

this nucleus doesn’t work in my body. I’m always hungry. Then we got our mammillary body here. The dorsomedial nucleus for sleep regulation

and food intake. You might wanna go into detail into this when

you study the physiology or neurology. But for now. That was the anatomy of the Diencephalon and

I hope that was helpful. Please put a like, comment, share, whatever

you find convenient to you. Our next video will be about the Telencephalon.