Alright Ninjas, in this video we are going to talk about the neuroanatomy of the pond. So let's go ahead and get started. Alright Ninjas, so what we are going to do is we are going to look at the kind of internal structures of the pond and then we will go into their function in more detail as we kind of move towards the right of the whiteboard. know is we have to look at two sections or cross sections or transverse sections of the pons.
One is going to be behind the left, it's going to be at the trigeminal nerve level, particularly at the level of the trigeminal motor nucleus. The one on the right is going to be at the level of the facial nerve or the abd... Duesen's nerve. Okay.
Let me give you guys a little orientation on that. So if I draw like a little mini diagram here, here's my cerebrum, right? Midbrain, pons, medulla, and then I have my spinal cord.
Here's going to be the cerebellum, right? The pons, you have a particular level here, right? At this level, we're going to have right here, is going to be at the level of the trigeminal motor nucleus, okay?
So, out from this, you'll have the trigeminal nerve, the motor nerve. And again, you'll have a sensory nucleus there as well. At the lower level, just a little bit lower, closer to that pons medulla junction.
So again, if I were to kind of draw like a line there, that's kind of right around the area between the pons and the medulla just below it. Right around that level, we're going to have the level of the facial nerve. And we're going to have this at the level.
of the abducens nerve, okay? So we're going to take two sections. One is going to be here, and that's going to be on the left. That's the level of the trigeminal, and we're going to take another section, and that's going to be at the level on the right, which is going to be at the level of the facial and abducens nerve, okay? Let's go ahead and focus here at the level of the trigeminal nerve.
All right, so let's go ahead and take a look here at this cross section at the level of that trigeminal nucleus, motor, and sensory nucleus here, okay? Now, what I want you to remember is that there's... a ventral portion here.
So when we're looking at this, giving you guys some orientation, this side here is the ventral, this side here is the dorsal. Okay. Or another way that we can say it is anterior and posterior. Okay.
Now, another thing is sometimes questions might come up where they might say, okay, what is the ventral portion of the pons called? In other words, here's your trapezoid body, right? We'll get into all these structures in a second, but this blue kind of like A diamond thing here is going to be the trapezoid body. Anything that is anterior to the trapezoid body, so from here all the way till here, this is the base or the basilar part of the pons, okay? Anything from this part of the trapezoid body all the way back here to the back part, most dorsal point, is the tegmentum of the pons, okay?
So again, this part, basilar part of the pons, This part all here, tegmentum of the pons. Okay? So, let's talk about stuff in the ventral or basilar part of the pons first. Then we'll get into all the structures in this dorsal or tegmental part of the pons next. Okay?
First things first, we have all these little orange dots within the basilar part of the pons. What are these little orange dots? These little orange dots here that we're going to talk about, we're going to have like a key so that this diagram doesn't get too crazy here.
These little orange dots are called your pontine nuclei. Okay? So these are called your pontine nuclei. And again, we'll talk about their function in a little bit. But one of the big things I want you guys to remember for this, and kind of that one word sentence, is that the pontine nuclei, what happens is you have descending motor fibers coming from the cerebral cortex that some of them will synapse on these pontine nuclei.
Then... When they synapse on these cell bodies, or these pontine nuclei, some of the fibers from the pontine nuclei on the left side of the pons will cross over to the opposite or contralateral cerebellum. The ones on the right side will cross over and send their axons from the right side of this pons to the contralateral or left cerebellum.
How do they do that? You see these black fibers here? If I were to kind of imagine here, here's going to be the synapse at this point. And from here, this guy is going to go this way. He's going to make his way across these.
These are your ponto cerebellar fibers, right? So what are these fibers here called? These are your ponto cerebellar.
fibers. And again, they're going from one side of these pontine nuclei to the contralateral cerebellum. When they go towards the contralateral cerebellum, how do they communicate with the contralateral cerebellum?
Do you guys remember? They're going to make their way. So for example, it would come down here to this guy. He would cross over this way, continue to keep crossing, continue, and then move into this little black structure here. What is this called?
These are called your middle cerebellar peduncles. Okay, so you have middle cerebellar peduncles. And again, we already talked about these when we talked about the midbrain.
Those are the superior cerebellar peduncles. If we're at the pons, it's the middle cerebellar peduncles. And if we're at the level of the medulla, it's the inferior cerebellar peduncles.
So again, what I want you to remember, and the basilar part, pontine nuclei. receive their information coming from descending motor pathways from the cortex to the pontine nuclei. When they synapse on the pontine nuclei, these pontine nuclei will send their axons to the contralateral cerebellum via the pontocerebellar fibers. These pontocerebellar fibers will then move into the middle cerebral peduncles, which will connect them to the contralateral cerebellum.
That's it. That should make perfect sense now, okay? Alright. We covered the basilar part. We're almost home.
Let's move on to the next part. If we covered the basilar part, let's go into this tegmental part. What do we say the tegmental part has right here at this portion? What do we say that was before?
That's the trapezoid body. Okay, so this is the trapezoid body. And we'll talk about what that is in more detail later. What I want you to know and that one kind of line sentence is the trapezoid body. is where the hearing, the cochlear fibers, okay?
So the fibers that are coming from the cochlear nuclei, they cross and they move up into what's called the lateral lemminiscus. We talked about that in the midbrain, okay? So the trapezoid body is gonna be these kind of like crossing of the cochlear fibers, or we call them the acoustic striae. We'll get into more detail on that. I just want you to know that this is basically where the crossing of the auditory pathway is.
Okay, now let's go a little bit farther back. We go a little bit more dorsal into the tegmentum and we have these purple structures and we're going to cover them on one side, but we're going to move from medial all the way out to lateral. Okay, so what are these structures as we go from medial all the way out to lateral?
So this would be the most medial portion here and this will be the most lateral portion. The most medial is the medial. As you go a little bit more out, then you have the trigeminal leminiscus.
As you move a little bit more out, you have the spinal leminiscus. And as you move all the way out to the lateral part, you have the lateral. Lemma Niscus. Okay.
We talked about these in great detail and the midbrain video, super quick little thing. Media Lemma Niscus carries sensory information from the dorsal column, proprioception, fine discriminative touch vibrations. The trigeminal Lemma Niscus is carrying touch pain, temperature, proprioception, pressure sensations from the face. The spinal Lemma Niscus is carrying Pain, temperature, pressure, crude touch from the neck all the way down. Okay?
And then the last one is the lateral liminiscus. And again, what do we say would happen from here just to kind of put this in perspective? There's a little bit of these fibers here.
Remember the trapezoid body? Some of these fibers will cross over and move into the lateral liminiscus. And we'll talk about where they come from. This will make more sense, but they do come here into the lateral liminiscus.
That son of a gun. That's carrying. Hearing. Okay, sensory information from the inner ear. Okay, particularly from the cochlea.
All right, so let's move a little bit more back. But again, let's hit these kind of blue structures here, then we'll work our way back to the midline. Okay, so we already hit medial meniscus, we hit the trigeminal, we hit spinal, we hit lateral meniscus, what's these blue structures here on the outer parts, this blue kind of like structures here are actually ascending fibers.
And these ascending fibers are a part of your ventral muscle. Spino cerebellar. Ooh. Spino cerebellar tract. And that is an ascending tract.
Okay, so it's carrying kind of these proprioceptive information, which is position sense from your muscles, your tendons, your joints, right? It's going to be sending that information to the cerebellum. And it actually will ascend up. It actually comes up through the medulla. It comes up through the pons.
And it comes up all the way up to the midbrain. and moves in via the superior cerebellar peduncles into the cerebellum. Okay?
So that's the next one. Let's move now into the middle here. We have these kind of these red tracks.
These red tracks here actually is a descending tract. This is actually the rubrospinal tract. Okay? This is the rubrospinal tract.
Remember this is a descending motor pathway to what? flexor muscles, okay, particularly of the upper extremities. Next one, the blue guy here.
This blue guy here is actually the tectospinal tract. You guys remember that one, the tectospinal tract, that's going to be sending descending information, motor information from the tectum, which is primarily the superior colliculus and inferior colliculus, down to the motor neurons. that are going to play a role within movements of the head the neck and even the eyes in response to either a visual stimulus from the superior colliculus or an auditory stimulus from the inferior colliculus okay all right let's move a little bit dorsal in the tegmental part of the pons right so we hit rubrous spinal we hit tectospinal what's this bad son of a gun this guy right here is your medial longitudinal fasciculus all right so what is this guy here if we come down here just use our key here this is the medial longitudinal fasciculus. You guys remember what that son of a gun connects? Remember this is basically coming from the sixth nerve, the abducens nerve, crossing over and connecting the third and fourth nerve, oculomotor and trochlear nerve, right?
So it's basically in the kind of an ascending tract that connects what? Three cranial nerves. Third, fourth, sixth cranial nerves. And it helps with basically conjugating our eye movements, making sure that they're coordinated, okay? So that's the medial longitudinal fasciculus.
Okay, this is actually a very common, important thing to remember because this can get damaged in patients with multiple sclerosis. We'll talk about that when we talk about multiple sclerosis, but it can lead to what's called internuclear ophthalmoplasia whenever this can be damaged, okay? Last thing here that we're going to talk about, then we'll kind of talk about these couple last structures here. Okay, you got this red nucleus here and this green nucleus. Again, what do we say we're at the level of?
The trigeminal nucleus, right? The trigeminal motor nucleus and the trigeminal sensory nucleus. Okay, so again, this red structure here is the trigeminal motor nucleus. The green one there is the trigeminal sensory nucleus.
So let's come down here and write that and get our key here, right? So the red one is the motor nucleus of the trigeminal nerve of cranial nerve five. If you guys watched our videos on each individual cranial nerve, we go into a lot more detail on the trigeminal nerve and how this is basically supplying the structures of the first pharyngeal arch.
Does that sound familiar? These are part of your special visceral efferent fibers, right? And that's supplying those muscles of mastication.
We'll talk about those in more detail later. The medial pterygoids, lateral pterygoids, masseter, temporalis, all those bad boys. So again, that's what his responsibility is for, okay? The green guy is actually going to be the sensory nucleus. Now, we're at the level of the pons, right?
So because we're at the level of the pons, This sensory nucleus is actually referred to as the central or principal pontine nucleus of the trigeminal nerve. So again, technically the sensory nucleus, since we're at the level of the pons, and particularly right at the level of the trigeminal motor nucleus, this is called the central or principal pontine nucleus. of cranial nerve 5 or the trigeminal nerve. Okay, so again, sensory nucleus, what is it picking up information from? It's picking up information, and we'll talk about this in more detail later, basically sensations from the face.
Okay, and we'll get into more detail on that, and if you guys want to know all about all these different fibers and nerves related to the trigeminal nerve, go watch our video. We have a specific video on the trigeminal nerve, okay? All right, so that covers all the internal structures at this point of the tegmentum.
Let's go a little bit farther back. Okay, what do we have next? All right, you see this guy here, big fluid-filled cavity. You know what this big fluid-filled cavity is called?
This big fluid-filled cavity here is called the fourth ventricle. And the fourth ventricle is a fluid-filled cavity filled with cerebral spinal fluid. And it's basically going to receive this fluid from the above cerebral aqueduct. So in the midbrain, you have the cerebral aqueduct, fluid drains down into the fourth ventricle.
Then from the fourth ventricle, we'll talk a little bit later, it can actually move out through the median or lateral apertures or the foramen luschia or the foramen magendi, or it can go down through the central canal into the spinal cord. Okay? Now, in the back part here, in the back part of the fourth ventricle, in the back part of the pons, you have this kind of like structure here. And this is called the superior medullary vellum.
Okay. So they call this the superior medullary vellum. Okay.
So again, we have the superior medullary vellum, and then just anterior to that, you have this fourth ventricle. Last thing is you have a tiny piece, a tiny little piece of the superior cerebellar peduncles and the dorsal part of the pons, a tiny little piece of that. So again, remember, what do we have back here?
In this most dorsal part, a tiny little piece of the superior cerebellar peduncles. Okay, you'll see this a lot in books where they'll have this. Again, I want you to remember that the main connection between the superior cerebellar peduncles is between the cerebellum and the midbrain. Middle is between the cerebellum and the pons, and inferior is between the cerebellum and the medulla. But again, for sense of anatomy, there is superior cerebellar peduncles, a tiny little piece of them, and this dorsal part of the pons tegmentum.
Okay. All right. That covers the cross section at the level of the trigeminal motor and sensory nucleus.
Let's now move on to the level of the facial and abducens. All right. So now we're going to take a look at the cross section of the pons, right?
But this is going to be at the level of the abducens and facial nerve. Okay. Sometimes people will just even say this is the level of the facial colliculus.
And I'll explain what that means in just a second. Okay. So again, giving you guys some anatomical orientation. This is the ventral.
This is the posterior or dorsal portion. So again, ventral anterior. posterior dorsal portion.
Again, giving you guys those terms, this part here, anterior to the trapezoid body, all the way to the most ventral portion. This is the base or the basilar part of the pons. Anything from the trapezoid body all the way back here, this is the tegmentum of the pons.
Okay. A lot of this should be review. Okay.
So we'll annotate. We won't write everything down. What is these guys going to be here in the, the actual Basilar part.
This is your pontine nuclei. I'm just going to put PN here, right? So PN, pontine nuclei. What are these guys that are going to move in the contralateral direction?
So again, if the descending fibers are coming down from the cortex to the pontine nuclei, these pontine nuclei are going to send fibers in the contralateral direction. What are these called? Pontocerebellar fibers. These pontocerebellar fibers will move in towards the direction of the contralateral cerebellum via the Middle cerebellar peduncles.
And again, same thing. If I have descending fibers coming to this pontine nuclei, it's going to send its information via these pontocerebellar fibers to the contralateral cerebellum via what structure? We already hit it.
It's the middle cerebellar peduncles. Okay, pontine nuclei. Pontine cerebellar, pontocerebellar fibers, middle cerebellar peduncles pretty much make up the basilar part.
Work our way backwards into the tegmentum. We already hit this before. This is your trapezoid body. All right, some of these structures here, after we go from the trapezoid body, we work our way back.
Some of these structures should be the same here, right? So this purple guy in the medial portion is the medial leminiscus. Work our way out. You would think, oh, that's the trigeminal leminiscus because that was the one before. Not really.
We'll talk about why in a second. What's the next one as you go a little bit more laterally? That is the spinal leminiscus. And you guys might be wondering, well isn't there supposed to be a lateral meniscus? Not yet.
Remember, we're at a lower level. We're at the facial colliculus level. The lateral meniscus hasn't formed.
But if you guys remember what forms the lateral meniscus, remember fibers from the cochlear nuclei will cross via the trapezoid body and come up as the lateral meniscus. Cochlear nuclei from this side will cross over and become the lateral meniscus. Okay. So we haven't formed the lateral liminiscus yet, but we have the medial liminiscus and the spinal liminiscus. Okay, work our way out a little bit more.
What was after the lateral liminiscus? Do you guys remember? That was your ventral spinocerebellar tract.
Again, that was carrying that proprioceptive information from, you know, again, your muscle tendons, your joints, your capsule within the ligaments, right? All of those different things. And then these are going to be coming up to the superior cerebellar peduncles. All right.
Let's now work our way a little bit more back. Okay. Let's hit these guys and we'll come back to these in just a second.
So we're going to come here to this kind of maroon colored guys here. These maroon colored guys, there's two parts of it, right? The ones that looks like the nuclei. This is going to be the spinal nucleus of the trigeminal nerve.
Let's write that down. So this nucleus part, okay, this guy here, this is your spinal nucleus of cranial nerve five or the trigeminal nerve. And we'll explain this in a little bit. The spinal nucleus extends from the lower part of the pons all the way down to the medulla, even a little bit into the portion of the spinal cord. Okay.
The other one is going to be the trigeminal. thalamic tract or part of the trigeminal leminiscus. So we're going to put here part of the trigeminal leminiscus.
It just, we're having some fibers coming off from the spinal nucleus that will move as the trigeminal thalamic tract or the trigeminal leminiscus that will move up into the upper level of the ponsal, which we had in the previous section. Okay. All right. We covered that bad boy.
Now. We're going to talk about what else this thing does in just a second because you'll see that this is connected to something else. There's this long axon coming off.
I'll explain in a second. Let's now move into this next component here. Okay, I want to circle something here.
Okay, I'm going to circle all of this. I'm going to put like kind of a dotted line here. All of these nuclei that are surrounded by this dotted line are a part of the facial nerve. Okay. They're all connected through multiple different sensory and motor systems.
If you guys want more detail on this, go watch it in our video on the facial nerve. What I'm going to do for right now is give you a little bit of explanation on this. So what I'm going to explain here is you have the facial nerve. It has multiple different sensory and motor fibers.
We're going to go from the purple one and work our way. And again, talk about this maroon color one last. Okay.
So the first thing that we have to talk about here, we have this purple guy, this purple nucleus, this purple nucleus with its axons that are going to be coming around. This is a part of the facial nerve, but this is going to be the motor nucleus of cranial nerve seven or the facial nerve. Give you guys a little bit of information about that.
Remember the facial nerve, the motor nucleus that supplies the supplying muscles of facial expression. And again, if you guys remember out of all those branches, right? So you have the temporal branch, you have the zygomatic branch, you have the buccal branch, you have the marginal mandibular branch, you have the cervical branch. It's supplying all those muscles of facial expression and even a little bit of the platysma. So if you guys want more detail on that, you guys go watch that.
But again, this is the muscles that are going to be supplied by the facial nerve. Okay. Now, because these muscles are actually a part of your pharyngeal arch, these are actually going to be muscles that are coming from the second pharyngeal arch. So these fibers we actually call special visceral efferent fibers.
Just like those motor fibers coming from the trigeminal nerve, those are supplying the first pharyngeal arch. So those are going to be special visceral efferent fibers. Okay?
The green one. Okay, the green nucleus is actually going to be a very special nucleus. This guy here is called the superior salivatory nucleus. And this is going to be connected to the facial nerve as well.
Now the superior salivatory nucleus, this is going to have its axons, its fibers, and these are going to be parasympathetic fibers. Parasympathetic fibers going to the lacrimal glands, going to your palatine glands, going to your salivary glands. So they play a role in lacrimation, nasal secretions, and salivation.
So these are parasympathetic nervous system fibers. But they're actually called general visceral efferent fibers of that facial nerve. Okay, go next one. The black nucleus here with its axons here.
This is actually going to be a very special nucleus called the nucleus of tractus solitarius. Right? It's cool to say that one.
The nucleus of tractus solitarius. This guy here. is actually going to be picking up sensory information from the anterior two-thirds of the tongue.
Taste. So that is actually a special kind of sensory system, right? So these fibers are coming from the tongue, anterior two-thirds of the tongue, they're picking up taste or gustation, and they're coming back to the pons. So these are special visceral afferent fibers, okay?
So, so far we have muscles, we have salivation, lacrimation, and nasal secretions. We have taste of the anterior two-thirds of the tongue. Guess what else we have? One more. Remember I showed you that the spinal nucleus of the trigeminal nerve was connected.
There was a connection to the facial nerve. I'll show it again in just a second. The reason why is, do you guys remember what I told you? What pretty much the nuclei of the trigeminal nerve are responsible for? They're receiving information, sensory information.
From the face, what kind of sensations? Pain, temperature, touch sensations. Well, you know another area that's actually really important that the facial nerve supplies?
It supplies the middle and external ear and even the tympanic membrane. So some of those sensations that you have within the tympanic membrane, the external ear and the middle ear are actually picked up on sensory fibers of the facial nerve. Okay? and sent to the spinal nucleus of the trigeminal nerve.
Okay? So again, this kind of maroon colored fibers, I want you to remember that these are general somatic afferent fibers, but these are fibers that are basically taking sensations. Okay? They're going to be taking sensations from the external ear, the middle ear, and the tympanic membrane.
But these are going to be, I just want you to remember, these are sensory. fibers and these sensory fibers are going to be sending this information to who? To that spinal nucleus of cranial nerve 5. Let me give you just a tiny explanation of that.
So if you look here let's just say that we take this part of the diagram. Let's say here is going to be picking up the sensations from the external ear your tympanic membrane. These sensations will be picked up via these sensory fibers of the facial nerve.
What kind of fibers? General somatic afferent fibers. They'll be traveling down this nerve. And as they travel towards what portion? Where are they going?
To that spinal nucleus of the trigeminal nerve. Okay? So again, that's what I want you to remember. They're picking up the spinal nucleus of the trigeminal nerve. It's receiving sensations.
Obviously pain, temperature, touch, pressure. Even a teensy bit of proprioception from the face. But also... from that external ear tympanic membrane and a little bit of the middle ear. All right, sweet deal.
Let's move on to the next part, okay? So we covered the facial nerve, okay? What's this guy here that it's wrapping around?
And we'll talk about what that little wraparound is called here because it produces a little depression in the back of the fourth ventricle. But let's talk about this nerve first. So we already covered the facial nerve and how it wraps around this nerve.
What is that guy called? That's called your abducens nerve. So again, what is this? son of a gun called here, this baby blue guy here that we talked about, this is your abducens nerve. And thank the Lord, the abducens nerve only has one fiber.
Okay. So again, this is your cranial nerve six, and it only contains motor fibers. Okay.
Or those general somatic efferent fibers. So if you guys really want to remember, that's your general somatic efferent fibers. And these go to your...
Lateral rectus, how do you remember that? LR6. Lateral rectus is supplied by the sixth nerve so it plays a role with abduction of the eyes. Beautiful.
We're done with that one. Thank goodness. Let's move on to the next structure. So we covered the abducens. We covered all the facial nuclei and their fibers.
Okay. And if we move out a little bit more, we got this guy here. Okay.
You see these red structures here. What are these? Okay.
This red structure here is actually a part of your vestibular nuclear complex. So again, what is it called? It's called your vestibular nuclear complex. So again, this is your vestibular nuclear complex.
And this vestibular nuclear complex has a couple different portions. It has a superior nucleus, a medial portion, a lateral portion, and an inferior portion. What I want you to remember is that the superior, middle, medial, and lateral portion are situated at...
this level of the pons the inferior is situated in the upper part of the medulla okay so you won't be able to see it okay so again superior medial and lateral at the level of this portion of the pons inferior won't be able to see it we'll talk about more detail what this guy does he plays so many roles if you guys want to know more about this in more detail watch our video on the vestibular cochlear nerve okay sweet deal let's go into the next one you see these green guys here These green nuclei here and then in the center of it is another big structure. Okay, we're going to talk about those now. These guys are your cochlear nuclei.
Okay, so you have your cochlear nuclei and if you guys want more detail on this, watch our video on the cochlear pathway of the vestibular cochlear nerve. But again, the cochlear nuclei, which are situated posterior to this brown structure or dorsal to this brown structure. It's called your dorsal cochlear nuclei. So what are these called?
Your dorsal cochlear nuclei. Sweet. The structure, this green structure that's located anterior to this kind of brown structure is called your anterior or ventral cochlear nuclei. So these are called your ventral cochlear nuclei. Sweet.
The next thing you have to answer is, okay, what the heck is this deuterobrown structure that's between these cochlear nuclei? This deuterobrown structure is actually the inferior cerebellar peduncles. There's a tiny little piece of the inferior cerebellar peduncles at this level of the pons. Okay. So again, what is this tiny little structure here?
It's called the inferior cerebellar peduncles. We're just going to put peduncles. Okay.
So the inferior cerebellar peduncle is separating posteriorly the dorsal cochlear nuclei, ventrally the ventral cochlear nuclei. Now, what I want you guys to know about this is the cochlear nuclei are receiving information from the cochlear branch of the vestibulocochlear nerve. We'll get into more detail on that. But again, if you have to remember these, I want you to remember that these guys are receiving information from the vestibular branch of the vestibulocochlear nerve. And guess what they do?
They send their information down into the trapezoid body, which will come out via the contralateral lateral meniscus. So again, you'll have fibers coming in through this guy. The ventral cochlear nuclei will send these fibers down through the trapezoid body. That's basically what makes the trapezoid body, is the crossing of the axons coming from the ventral cochlear nuclei, or what we call the ventral acoustic striae.
Okay? It'll cross over and go to the opposite side and make the contralateral lateral meniscus. Beautiful, right? Okay, sweet.
Next thing I want to talk about here, we have these green structures here. These green structures here are also very important. Again, we'll talk about that in a little bit more detail when we go over this kind of trapezoid body and the cochlear nuclei in more detail. But what happens is some of these fibers from the trapezoid body.
that ventral acoustic striae basically, will ascend upwards, right? And some of those fibers, as they go upwards, will synapse on these structures. And they play a role with being able to play a, determine the intensity, as well as kind of the relative velocity of auditory sensations. What are these guys called? These green guys here, which we're going to kind of annotate here, these are called your superior olivary complex or nucleus.
So this is called the... Superior Oliveri Nucleus Okay, so they play a role with the relative intensity, timing, velocity of auditory sensations. And they're a very important component of that auditory pathway.
We'll get into more detail on that in a little bit. What else do we have? We have these guys. Remember these?
Rubro spinal tract, descending motor pathway to the flexors. Tecto spinal tract, helps with reflexive movements of the head and the eyes. And the medial longitudinal fasciculus, which is the connection between the sixth, the third, and the fourth.
cranial nerves. Move a little bit back. Remember I told you that there was a thing called the facial colliculus. And basically what that is, is whenever the facial nerve, where we have it here, it kind of rolls around the sixth nerve. It puts a little depression into this portion of the fourth ventricle.
So what is this structure here? Again, we still have the fourth ventricle. But there's a little depression on both sides here.
What are those little divots called? This is called your facial colliculus. Let me give you guys a little bit better review of this so you completely understand here. I'm going to draw a sagittal section here.
Okay, so here's your midbrain. Here's your pons. Here's your medulla.
And here's your spinal cord, right? And then here's your cerebellum. And then what we'll do here is we'll draw a little.
sitting there for the fourth ventricle. Again, to explain it like this, here's your sixth nerve, your abducens. We'll put here in black here.
This is your facial nerve nucleus. And again, all of those fibers that are coming from the multiple nuclei, they wrap around. And when they wrap around, they put a little divot into this little fourth ventricle. That little divot, which is formed by the turning of those facial nerve fibers is called the Facial colliculus.
Okay? So that covers all the components within this section of the pons. Alright guys, so now that we've covered pretty much the cross sections, covered pretty much all the internal structures, things that are coming in and out of the pons at the trigeminal level, and at the facial nerve abducens level, I kind of want to give just a general overview with different kind of like sections so that we completely understand all of these structures.
Just a general overview of what these structures are that are moving up, that are moving down, that are moving all over the place in these levels of the pons. Again, they're going to be very general. They're not going to be super detailed. I just want us to get the overall concept. First thing I want us to understand is the level of the corticoponto cerebellar fibers.
Okay, so again, if you guys remember, we have these descending motor fibers. So here's your upper motor neurons, right? They're coming from the cerebral cortex. They're coming down, and as they come down, remember what happens. They move through the crust cerebri, and some of the fibers will scatter around the pontine nuclei, and some will actually synapse on these pontine nuclei.
When, again, some of these come together, they move down to the level of the medulla at the pyramids, cross over, right? So some of these will re-come together, cross at the level of the pyramids, and come over here, okay? What I want you to remember is that some of these fibers that are coming down here that stop at the pontine nuclei, they'll synapse on these pontine nuclei, right? These pontine nuclei, what did I say? They'll send their fibers, their pontocerebellar fibers, to the contralateral cerebellum via the middle cerebellar peduncle.
So the middle cerebellar peduncles are basically these structures here that are connecting the cerebellum to the pons, right? So again, Cortex coming down to the pontine nuclei, synapse on some of those pontine nuclei. The pontine nuclei will send their fibers via the pontocerebellar fibers via the middle cerebellar peduncles to the contralateral cerebellum.
What is the purpose of this? What will happen is you have a motor plan. Motor plan is coming down to go to the muscles. You perform a movement. Your cerebellum is also going to be receiving sensory information from a bunch of different proprioceptors from those muscles that are firing.
Your cerebellum receives that information from all these sensory pathways. It also receives the previous motor plan that came down from the cortex. It takes all that information, sifts through it, and then guess what it'll do?
It'll send that information back up to the cerebral cortex and say, Hey. I took into consideration the movement that you had planned. I received all the sensory information from the muscles, the tendons, the joint capsules. I put it all together, came up with the next perfect motor plan. Here's what you need to do.
Isn't that cool? So again, that's the thing I want you guys to understand with those pontine nuclei, the pontocerebellar fibers, and again, the middle cerebellar peduncles. Okay, next thing.
Again, we've talked about these fibers in so many videos. We're going to make this very general. We're going to go over some of those ascending pathways.
Okay, again, let's cover the medial liminiscus and we'll kind of work our way outward. So we'll do medial liminiscus here in purple here, right? So medial liminiscus.
What does it do? It receives sensory information from proprioceptors for finding a discriminative touch for vibrations. And what does it do?
It sends that information inwards, comes into the dorsal gray horn and moves into the dorsal gray horn and ascends upwards on the ipsilateral side, comes to the medulla where it has nuclei like the nucleus cuneatus and the nucleus gracilis, right? Synapses on these nuclei in the medulla. And then what happens? These guys will form those, that arcuate fibers, the internal arcuate fibers, which will cross and ascend upwards.
And as it ascends upwards, it eventually goes to the thalamus. Where is these medial limoniscus fibers? Remember, they were at the pons at both levels.
So that's, again, picking up sensory information from proprioception, touch, and vibrations. What else do we have? Let's do the maroon as the trigeminal.
Again, the trigeminal nerve, remember you have the spinal nucleus here, you have the central principal pontine nucleus, and the mesencephalic nucleus, right? And these guys are receiving information from the trigeminal nerve, all the sensory fibers. And from these nuclei, they basically send up their axons as the...
trigeminal lemniscus. So again, you're going to have the, what is this here? The mesencephalic nucleus, the central or principal pontine nucleus, and the spinal nucleus.
They're going to be receiving information, pain, temperature, touch, vibration, all of those things from the face and sending it to these individual nuclei. And these individual nuclei will send up their axons as the trigeminal lemniscus. Okay. So again, purple here. is medial limoniscus.
The maroon here is the trigeminal limoniscus. What else do we have? So the next one in this kind of like do to green color, this is your spinal limoniscus.
Do you guys remember what happens with a spinal limoniscus? Spinal limoniscus, you're picking up pain, temperature, crude touch, and even some pressure. That sensory information is coming in.
It's synapsing on that dorsal gray horn. If it's pain and temperature, where is that going? Lateral.
If it's going to be crude touch and pressure, where will those fibers go? Ventral. Either way, they'll eventually ascend upwards and come together. And when those fibers come together from the ventral spinothalamic tract and the lateral spinothalamic tract, they'll ascend upwards as the spinal lemminiscus. Okay?
So again, medial lemminiscus is carrying that proprioception. Find discriminative touch and some of the vibrations. Trigeminal meniscus carrying all those sensations from the face.
Spinal meniscus carrying pain, temperature, crude touch pressure from the basically from the neck down. Okay, that covers those. And if you guys really want to remember here, remember we said that there was also another ascending pathway, that ventral spinal cerebellar tract. If you guys really want to remember that one, it's also kind of doing the same thing here. as this pathway here, it's picking up sensations.
What kind of sensations? It's picking up sensations from proprioceptors, from muscle, tendons, joints, from L2, L3 level down to the coccyx. Okay. And it sends that information into the dorsal gray horn, crosses over to the lateral white column and ascends upwards.
And what do we say it does? It goes into the superior cerebellar to the contralateral cerebellum. Okay.
Okay, that covers that one. And again, if you guys really want to remember what happens here, once it goes through the superior cerebellar peduncles, it actually will go into this part of the cerebellum and actually move behind and go to the opposite cerebellum. So again, just a little tiny piece of information there. Technically, the ventral spinal cerebellar tract will take proprioception from the same side to the same cerebellum.
It just goes up through the superior cerebellar peduncles of the contralateral cerebellum and then moves... around the midbrain to the other cerebellum. Pretty crazy.
But again... This covers a lot of those tracks that we talked about and puts a name and a kind of an idea behind all of those structures. Okay, now that we covered some of those sensory pathways, let's cover another one, which is basically that vestibular nuclear complex.
Okay, so if you guys remember, we have your vestibulocochlear nerve. Remember, the vestibulocochlear nerve is going to be receiving information from your ears, right? Particularly from the inner ear. So it's going to be coming from that cristae ampullaris and the vestibule, right? And what happens is that information will come in, and when it comes in, it'll actually move over here and synapse on these vestibular nuclear complex.
So again, this is coming from your inner ear, okay? Picking up your dynamic and kind of static equilibrium. Okay, so movements of your head, up and down movements, all that stuff. From the ears, it'll send it to your vestibular nuclear complex.
Do you guys remember what your vestibular nuclear complex does? It actually can send information downwards and go down to your muscles, okay? So it actually will go down to your muscles, and it'll actually cause stimulation of the muscles that are going to be going to extensor. So it's going to actually stimulate.
your extensor muscles, okay? And that's called your vestibulospinal tract. And I just want you to remember that's going to your extensor muscles, okay? Your anti-gravity muscles.
That's one thing. So it helps you to kind of keep your balance and your posture whenever there is this movement, okay? The other thing it does, it sends information from the vestibular nuclear complex via the inferior cerebellar peduncles to your cerebellum.
Do you guys remember that nucleus in the cerebellum? This was called that vestigial nucleus, right? Or that juxta-restiform body that you have the connection between. This helps us to maintain, again, a dynamic equilibrium. Again, cerebellum wants to receive all kinds of sensations because it is important for posture, for balance, for coordination.
Vestibular nuclear complex also does what else? It sends a stimulus to the contralateral sixth nerve. Then that contralateral sixth nerve, guess what he does?
Hilt, let's do this in a different color. Let's do it in green. This sixth nerve will send information upwards to the contralateral third nerve and fourth nerve.
So again, you're going to have three, four, six. You're going to have vestibular nuclear complex simulates the contralateral sixth nerve. The contralateral sixth nerve will then move over and stimulate the contralateral third and fourth nerve nucleus.
Guess what this structure is called? The medial longitudinal fasciculus. And we saw that at both sections. Okay.
So we've already covered the vestibular nucleus. We covered the medial longitudinal fasciculus, and we already talked about the abducens nerve. Okay.
That covers some of that structure. Now let's move on to the next thing here, which is coming down here to talk about the cochlear pathway. All right.
So we talked about the vestibular nuclear complex. We reviewed the medial longitudinal fasciculus. Let's now talk about these cochlear nuclei, okay?
And the superior olivary nucleus, which we said we'd talk about. Remember, coming from the cochlea, again, the vestibular cochlear complex is connecting between the vestibule, right? The chrystampularis, so your inner ear, playing a role with dynamic and static equilibrium. The cochlea, on the other hand, is taking information for auditory sensation, hearing, okay? Nothing to do with equilibrium.
cochlear fibers that are part of the vestibulocochlear nerve will actually synapse, okay, on these cochlear nuclei, which we already talked about, right? And again, you have the cochlear nuclei, which is the dorsal cochlear nuclei here in the back, and the ventral cochlear nuclei here in the front. And again, what separates those is the inferior cerebellar peduncles, right? These cochlear nuclei, what do we say happens? Some of these guys will actually go upwards.
And it formed like that dorsal acoustic and intermediate acoustic striae. But a lot of them from the ventral cochlear nucleus will cross over. And when it crosses over, it'll synapse on that superior olives, right? That superior olivary nucleus. So again, some of these fibers will just cross right over, won't go to the olives.
And then some of the ventral acoustic striae fibers will cross over and then stop at those superior olives. Either way, all of that crossing that you have here, all of this is that trapezoid body. That's where all those fibers from the cochlear nuclei, which are moving to the contralateral side whenever they're crossing, that's what's forming that trapezoid body. Then some of these fibers will synapse on the superior olivary nucleus, and the superior olivary nucleus will also give off some fibers that'll move with some of these other fibers coming from the cochlear nuclei that didn't synapse.
These guys will come up, and whenever they come up, this structure here. that we formed after the trapezoid body, this right here is your lateral leminiscus. Okay. And again, if you guys remember the lateral leminiscus will come up, it's taking auditory information.
So it'll actually go all the way to this structure here called the inferior colliculus. And from the inferior colliculus, the breaking of the inferior colliculus will connect to the thalamus. And then from the thalamus, this will send that information. to the primary auditory cortex, or remember the superior temporal gyrus or the transverse gyrus of Heschel.
That's that auditory information. But again, I wanted to kind of give you an idea. What is the trapezoid body? It's the crossing of the fibers coming from the cochlear nuclei, and the lateral lemminiscus is basically taking up. It's the ascending fibers of that auditory pathway moving up through the pons, through the midbrain, terminating at the inferior colliculus.
And again, Some of these fibers that are crossing after the trapezoid body, some of them do synapse on those superior olives. To give a roll with relative intensity, relative timing, and velocity of sound. Sweet deal. Next thing I want you guys to remember here is going back to that tectospinal and that rubrospinal.
Again, we're not going to go into crazy detail because we've already talked about this. But I just want to give you guys an understanding. Remember what the tectum is? The tectum is going to be the superior colliculus and the inferior colliculus, right?
that dorsal part of the midbrain. That tectospinal tract is going to be descending motor fibers that are giving off connections to your cranial nerve nuclei that play a role within movement of the eyes. So third, fourth, sixth.
And down to the lower motor neurons in your spinal cord that'll go to the muscles of the head and the neck to move the eyes. Right? So again, tectospinal tract is the motor fibers going to muscles of the eye. And muscles of the head and the neck for movement.
If the stimulus is coming from the superior colliculus, that's visual stimulus. If it's going to be inferior colliculus, that's auditory stimulus. Okay?
A simple example, again, you're seeing somebody that's walking, you're moving your head and your eyes towards that direction. You hear someone yell your name over here, when you hear them yell your name, you look towards that direction, you fix your eyes, your neck, and you gaze towards that area. If you're tracking superior colliculus, if you're moving in response to an auditory stimulus, inferior colliculus. Simple as that. The other one, this red guy in the level of the midbrain here, we have the red nucleus and the red nucleus is sending down these descending motor fibers that are going to be going to muscles that play a role with flexion, primarily the upper extremity distal flexors.
Okay. This tract is the rubro spinal tract. So again, putting an idea or concept behind the tectospinal and the rubrospinal tract.
What are their functions? We already know. Okay, sweet. Let's move on to the next thing. The next thing that we have to talk about here is going to be looking at that ventricular system.
Again, I just wanted to give a different view. Okay, so if you look at a sagittal view here, we have this kind of like horn structure here. This is our lateral ventricle.
So we're just going to kind of like abbreviate this lateral ventricle. Then connecting the lateral ventricle to this third ventricle, okay, so this is the third ventricle, is this little connection here called the interventricular foramen or the foramen of Monroe. Then the third ventricle drains down via the cerebral aqueduct. And then from the cerebral aqueduct at the level of the pons and the medulla, we get the fourth ventricle. And then the fourth ventricle can continue downwards as the central canal.
Okay. Or it can come out and go into the subarachnoid space via the median and lateral apertures. To give another view, this is going to be looking at that ventricular system from the posterior portion. Okay. All right.
So again, here you're going to have midbrain, here you're going to have pons, here you're going to have the medulla. If we look here, this obviously is the cerebral aqueduct. And then this whole thing here is the fourth ventricle. Sometimes they might ask questions in regards to the external structure.
So really quickly, what is this line here right down the middle? This is called the median sulcus. We're not going to write it down. I just want you to remember it. Okay, that purple, that pink line is the median sulcus.
The next thing, sometimes they'll ask, what is this structure here? These kind of like black kind of structure here on the sides of that median sulcus. And that black structure there on the side of the median sulcus is called the median eminence.
Okay, at the bottom of the median eminence, there's a little divot here. Let's do this one in green. This little divot here in the bottom of the median eminence is actually called your facial colliculus.
Okay? That's that little depression in the back of the pons formed by when the facial nerve turns around. Okay?
So again, pink line, median sulcus, black structure on the side of it is the median eminence. At the bottom of the median eminence is going to be the facial colliculus. The last thing is on the outer parts here.
Let's do this in red. on just outside of the median eminence is called your sulcus limitans. Okay.
So sometimes they might ask you this, what is the median line structure? It is called the median sulcus on the sides of the median eminence at the bottom is the facial colliculus and all the way lateral is the sulcus limitans. Last thing I need to tell you is there is a kind of a horizontal line here coming from this portion here to this portion here.
This here, this brown structure is called the stria medullaris. The stria medullaris is important because above the stria medullaris, that portion of the fourth ventricle is actually going to be formed by the back of the pons. Below the stria medullaris, that portion of the fourth ventricle is actually going to be formed by the back of the medulla.
So sometimes they might ask you that question as well. Okay, last things that we got to talk about here. We gotta talk about the abducens nerve, okay? And again, this is very general. We're not gonna go into tons of detail here.
We already talked about these in great detail in these individual videos. But if you guys remember the abducens nerve, what extraocular muscle does this bad boy supply? It supplies the lateral rectus.
And again, what does the lateral rectus do? He plays a role in abduction of the eyes. Okay, done.
Facial nerve. Again, we'll go into more. You can go watch our video.
We go over this in way more detail, but I want you guys to get the basic concept here. What does it do? If you have those fibers, that special visceral efferent fibers, the second pharyngeal arch is supplying all the muscles of facial expression. So it supplies muscles of facial expression. Okay, sweet.
Superior salivatory nucleus. What does that guy do? He's taking the actual sensations from where? He's actually sending visceral efferent information to where?
To the lacrimal glands, to the nasal glands, and to your salivary glands. Okay? So it's also going to play a role in lacrimation and salivation. Okay.
Sweet. What else? We're also going to have that nucleus subtractive solitarius.
What is that guy doing? It's taking sensory information. of taste from the anterior two-thirds of the tongue.
So it's also going to play a role in gustation. What is gustation? Gustation is taste. Okay.
And again, we'll put here two-thirds, anterior two-thirds of the tongue. The last thing is it's also going to be taking up from that spinal nucleus of the trigeminal nerve. You guys remember what that picks up? The general somatic efference, which is the pain, the touch, the temperature sensations coming from the external ear and the tympanic membrane and a little bit of the middle ear. So it's also going to pick up sensations from ear.
Okay. And again, just remember external ear, middle ear, and tympanic membrane. Okay. The last sucker that we got to talk about here is the trigeminal nerve. And again, we already covered this in great detail in the trigeminal nerve video.
Just to do a very basic overview, trigeminal nerve. We have those. special visceral efferent fiber supplying the first pharyngeal arch.
That's going to be the muscles of mastication. Okay? So it's supplying the muscles of mastication. And again, what nucleus is that going to be coming from? That's going to be coming from that motor nucleus of the trigeminal nerve.
What was the other nucleus of the trigeminal nerve? I'm glad you guys asked because we got a bunch of those, right? At this level, at the midbrain, right?
So we have the midbrain. Here we'll have like a kind of line here to separate each portion. We have this portion here, midbrain, is above that. Here we have the pons. And then here we have the medulla.
Okay. At the midbrain level, what is this nucleus here called? The mesencephalic nucleus. Okay. What is this one called?
That principal or central pontine nucleus. And this one here, which is actually a little bit in the lower part of the pons and the medulla is the spinal nucleus of the trigeminal nerve. What are all of these guys receiving? This one's primarily receiving proprioceptive information from the muscles of the jaw.
The principal is primarily receiving fine and discriminative touch from the face, a little bit of proprioception. And the spinal nucleus is receiving pain, temperature, touch, pressure, and a teensy bit of proprioception from the face. Easier way to say that is all the sensations of the face.
Okay, so sensations. of face. And again, if you guys want more detail on all of those different areas of the face, go watch our video on the trigeminal nerve.
Okay. But that covers all these different parts here. All right, engineers. So in this video, we talk a lot about the pons. I hope it made sense.
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