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 medulla oblongata.

So remember, 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 medulla oblongata, which is here.

So in this video, we’re first going to cover  the external surfaces of the medulla. Basically,

look at its topography and what structures you’ll  find from an anterior view and a posterior view.

Then we’re gonna slice up the medulla  and look at the internal surface.

Basically, see how the grey matter and white  matter are arranged within it. And at the end

of this video, you’ll find a quiz that you’ll  hopefully be able to pass based on this video.

Alright, so we can start by replacing  this picture with a more realistic one.

The medulla is here, lying right above the spinal  cord and below the pons. The medulla also connects

with the cerebellum, so you’ll find the cerebellum  behind the superior part of the medulla oblongata.

And all of these structures lie within  our cranial cavity within the skull.

So topographically, the medulla starts  at the level of the foramen magnum,

which is the distinct border between the  spinal cord and the medulla. And in the front,

the medulla lies on the clivus, which remember  is at the anterior portion of the occipital bone.

The length of the medulla oblongata is  about 2,5cm, so it’s a quite small portion

of your brain but a very important one. Alright. Now. Externally, your medulla has

two surfaces. It has an anterior surface and a  posterior surface. Let’s now cover the typical

morphology of these two surfaces, starting with  the anterior surface first. So if we look at the

brainstem from this perspective, you’ll see this. And again, the medulla oblongata is here in green.

So there are 5 grooves that you can see on the  anterior surface. The first one is the Anterior

median fissure, then laterally to that, you  can see the Right and Left Anterolateral sulci,

and laterally to that again, you’ll see  the right and left posterolateral sulci.

And notice between these grooves, there are bumps  that are very characteristic for the medulla.

The first bumps are called the Pyramids of the  Medulla Oblongata. And they’re located medially

between the anterior median fissure and the Right  and Left anterolateral sulci. The pyramids contain

the corticospinal tracts, which come from the  pyramidal cells of the primary motor cortex. Which

remember is responsible for voluntary movements of  our skeletal muscles. A majority of the fibers in

the corticospinal tract will decussate at  the lower border, forming the decussation

of the pyramid. We’ll talk more about that when  we talk about the internal surface of the medulla.

I just mentioned it now to give you something to  remember the pyramids with. Alright. Laterally to

the Pyramids, you’ll find the Olives of the  Medulla, which contain the olivary nucleus.

So these are the bumps. But some cranial nerves  go out from the medulla through these grooves.

We have 12 cranial nerves in our body and each  serves its particular function in the brain,

but from the anterior part of the medulla. You’ll  see the 12th cranial nerve, the hypoglossal nerve,

going out from the anterolateral sulci. The 12th  cranial nerve is responsible for the movement of

most of the muscles in your tongue, so this  nerve goes out from the anterolateral sulcus

and then goes to the tongue. So that is  that. Then on the posterolateral sulci,

there are three cranial nerves that go out.  These are the cranial nerve number 9, number 10,

and number 11. The glossopharyngeus, Vagus, and  the Accessorius. Glossopharyngeus is mainly for

coordinating the swallowing process and  is also responsible for the gag reflex.

Vagus goes to most organs in your body and  regulates their function. Mainly parasympathetic

fibers. And the last accessories is an  accessory nerve for the neck muscles.

So that is the anterior view. Now let’s turn the picture around

and look at the posterior view. So the posterior  part of the medulla is highlighted in green,

and if we now remove the cerebellum, you’ll  be able to see the rest of the medulla. Now

the upper part of the medulla oblongata takes part  in forming the so called rhomboid fossa, which is

a fossa that contain many nuclei. The lower part  of the rhomboid fossa is considered a part of the

medulla oblongata, but we’ll cover the rhomboid  fossa briefly in a separate video to really focus

on the anatomy of the medulla for now. So on the posterior surface,

you’ll find the Posterior median sulcus. On  either side of the posterior emdian sulcus,

you’ll find the Gracile Fascicle, remember  we talked about this one when we talked about

the spinal cord. The gracile fascicle received  sensory input form the Lower part of your body,

and sends it up through the spinal cord and  through the medulla, to the gracile nuclei,

which form a gracile tubercule. Laterally to  the gracile fascicle is the Cuneate Fascicle,

which receives input from the upper parts  of your body and forms the Cuneate Tubercle.

From the posterior surface of the medulla,  you’ll also be able to see the inferior

cerebellar peduncles, which are fibers that go  within the medulla, to the cerebellum, as you

see here. So the inferior cerebellar peduncles  connect the cerebellum and the medulla together.

So that was all for the  external surface of the medulla.

Now let’s go ahead and cover the internal  surface of the medulla oblongata.

The internal surface of the medulla consists of  two parts, grey matter, and white matter. And

just to remind you again, that grey matter always  contains cell bodies, so when we talk about the

grey matter, we talk about nuclei. White matter  always contains nerve fibers, which form tracts.

Now, let’s finally take the medulla and give it a  good slice, to focus on the internal surface. In

theory, if you wanna go deep within the neurology  of it, the internal surface of the medulla differs

along the superior part and the inferior part of  it. Meaning if you cut the medulla at different

regions, you’ll find different structures. But in  this video, I’ll just slice at the superior part

of the medulla and talk about the most significant  parts of the internal surface while highlighting

which parts below to which level so that it  gets easier to understand the medulla oblongata.

So here is the general outline of the medulla.  We’ll be able to see the Antrior median fissure,

the Pyramid of the medulla and the Olives. And  posteriorly, we’ll see the Gracile Tubercle and

the Cuneate Tubercle. And on the sides here  we can see the inferior cerebellar peducle,

which remember connects the cerebellum with the  medulla. So I hope you’re following so far. Let’s

now go ahead and fill upp the internal surface  with structures, starting with the grey matter.

We’re first going to have the Gracile Nucleus  medially, within the gracile tubercle. Then

laterally to that, we have the Cuneate Nuclei,  within the cuneate Tubercles. Within the Olives,

we have the olivary nuclei, and then in the  middle, we have the Reticular formation,

which is a network of grey matter throughout  the brainstem. I’ll show you this in a little

more detail later. Then lastly, you’ll find many  nuclei of the cranial nerves within the medulla,

at the region of the Rhomboid Fossa. You’ll  find the cranial nuclei number 8-12. Again,

these are not significant for the understanding  of the medulla anatomy, for now, so I’ll mention

these in the video about the rhomboid fossa.  So these are the grey matter of the medulla

oblongata. Let’s now see how these nuclei are  associated with tracts within your brainstem

by looking at the white matter of the medulla. While we’re talking about the tracts,

I’ll represent the blue color as ascending  tracts or sensory tracts. And the red color

will represent motor tracts or descending tracts.  Alright, so first off, we’ll start with the

fibers associated with the nucleus gracilis, and  we’ll add the spinal cord to visualize this one.

Fibers that synapse with the nucleus gracilis are  sensory fibers that come from the lower parts of

the body and through the spinal cord. These fiber  will then ascent and synapse with nucleus gracilis

in the medulla. Um, I use the letter G in Gracile  nucleus as genitals to remember that nucleus

gracilis receives input from the lower parts of  the body. And it receives conscious epicritic

sensibility. With is conscious proprioception.  Remember, this is kinesia, joint position,

and the sense of force. But it also receives input  from mechanoreceptors, which is responsible for

two-point discrimination, which means the minimal  distance between two points required for you to

detect it as two points and not one. So if these  two pencils were veeery cloe to each other, you’d

have detected that prick as one point and not  two. So two-point discrimination is your ability

to discriminate between two points. Meaning the  minimum distance needed for you to sense those

pencils as two points, not one. It also receives  input like vibration and touch. All of these are

sent to the nucleus gracilis. The cuneate nucleus  receives input from the upper part of your body

through the cuneate fascicle, which also senses  epicritic sensibility. Alright. Now from the

gracile nucleus and the Cuneate nucleus, where do  the fibers go? Well, they split into two pathways.

They split into fibers that go through the  inferior cerebellar peduncle, as you see here,

as fibers called the external arcuate fibers.  And remember, since they go through the inferior

cerebellar peduncle, they’ll go to the cerebellum. Now. Since we have external arcuate fibers,

we’ll also have internal arcuate fibers. And  these fibers will cross over to the other side,

as you see here. So these are called the internal  arcuate fibers. And since both sides cross to the

other side, they decussate to form the decussation  of the lemnisci. They’re called that because once

they cross, they start to ascend upwards  in your CNS, as the medial lemniscus. To go

further through the diencephalon and then to the  primary somatosensory area in the cerebral cortex.

Next, we have two tracts on either  side. Called the spinocerebellar

tracts. Remember we talked about these  when we talked about the spinal cord?

We have an anterior spinocerebellar tract and a  posterior spinocerebellar tract. Remember, if the

tract ends with the work Cerebellum, that means  that these tracts will ascend to the cerebellum.

But the way these two tracts do that is a little  bit different. The posterior spinocerebellar

tracts are closest to the inferior cerebellar  peduncle, so it’ll go through the inferior

cerebellar peduncle to the cerebellum. The anterior spinocerebellar tract

will ascent through the medulla oblongata through  pons and then to the midbrain. From the midbrain,

it’ll go into the cerebellum through  the superior cerebellar peduncle.

And since these tracts go to the cerebellum,  that means they’re responsible for

unconscious proprioception, like giving  information about the posture and joints.

After that we have two other ascending  tracts, called Spinothalamic tracts.

We have an anterior spinothalamic tract and  a lateral spinothalamic tract. These tracts

are both going to go to the primary somatosensory  area in the cortex. And as they ascent, they get

the name the spinal lemniscus. And since they go  to the cerebral cortex, that means they provide

conscious sensory information. And that is for  Pain and temperature and pressure and touch.

So that was all the ascending tracts  I wanted to mention in the medulla.

Now let’s do the descending tracts. And the first one is the one that’s

the most significant of them, located within the  pyramids of the medulla, called the corticospinal

tract. These fibers will originate from the  pyramidal cells of the primary motor cortex,

and then they will descend. 80 percent of  the fibers that descend, will cross at the

medulla oblongata region, like this, and form the  deccusation of pyramids. After they cross, they

will descend as the lateral corticospinal tract.  The remaining 20% will descend as the anterior

corticospinal tract, and only decussate at the  region they exit at the spinal cord. And since

they come from the pyramidal cells of the primary  motor cortex, that means they’re responsible

for the voluntary movement of skeletal muscles. Next there are the corticonuclear tracts, which

descend at the same areas as the corticospinal  tract. And the corticonuclear tracts are

responsible for the voluntary control  of muscles located in the head and neck.

The next descending tract is the vestibulospinal  tract. Inside of your ear, the inner ear,

you have a system called the vestibular system.  The vestibular system has crystals within it

sensing the position of your head, wether your  head is tilted upside down, or to the side, all of

that is sensed and through the vestibular nerve,  it’s sent to the brainstem, and then down to your

spinal cord to keep your balance and posture.  So the vestibulospinal tract is responsible for

keeping your balance and posture. And this happens  unconsciously because this tract doesn’t originate

from your cortex—so unconscious balance of  your body is the function of this tract.

So that is the Vestibulospinal tract. Next we  have the Olivospinal tract, which comes from the

olivary nuclei. The olivospinal tract also takes  part in helping you keep your balance and posture.

Through the olivary nuclei, there are  also fibers that go to the cerebellum,

called the olivocerebellar tract, which  aid the balance system. So that’s these.

Next, we have the Rubrospinal tract. Rubro means  red, and the reason why they’re called rubrospinal

tract Is because we have red nuclei located inside  the midbrain of the brainstem. So these fibers are

extrapyramidal because they’re not originating  from the primary motor cortex. They come

from the red nucleus of the midbrain, and they  descend as the rubrospinal tract. And remember,

extrapyramidal fibers are responsible for fine  coordination of movements and support voluntary

movements, they make our voluntary movements  more precise. SO that is the rubrospinal tract.

The next tract is the tectospinal tract. It  transmits motor impulses for the eyes and

neck muscles. So they coordinate the eyes and  the neck muscles when you look at something.

Imagine you’re looking at a hamburher, you look  at it, and you keep looking at it as it passes you

and your neck muscles follow your eyes. That’s  what this tectospinal tract is responsible for.

It’s called tectospinal tract because it comes  from the tectum of the midbrain, it’s located

on the posterior surface of the midbrain.  It’s also extrapyramidal, so it unconsciously

moves your neck muscles with your eyes. Then we have the Reticulospinal Tract.

We have a lateral Reticulospinal tarct, and a  medial reticulospnal tract, which are also a

part fo the balance and posture system. They come  from the reticular formation inside the brainstem.

The Reticular system are responsible for  Sleep, alertness, cardiovascular control,

breathing and all of those vital things. But  they’re also responsible for motor control

like your balance and posture, through the  reticulospinal tract. So that is all of these.

Let’s just clean up the labels and add  a little colour to differentiate them.

There is one more tract that we need to mention,  which is the medial longitudinal fascicle,

which descend and is present only in the cervical  segments, which coordinated involuntary movements

of the head, neck, and eyes through  synapses between the cranial nerves 3,

4, 6, and 11. So that was all I had for the  internal surface of the grey and the white matter.

I made this table for the nuclei in the grey  matter and the tracts in the white matter we

just went through, along with a little description  of them. Now this Is where this video gets scary.

I am going to make all of these names disappear,  and can you, from the beginning, tell me what is

the name of number 3, what is the name of number  4, where does number 6 go and where does number 11

go. If you can do that, then you’ve grasped  the anatomy of the medulla oblongata fully.

If you found this video helpful, please  put a like, comment, share, whatever

you find convenient to you. The next video is going to be about the Pons