Hello my dear anatomy students, how are you? Welcome to another new installment of this easy anatomy channel by Juan José Sánchez. Today I bring you a video of a structure of the posterior brain, of a rhombencephalic structure, I bring you the anatomy of the famous medulla oblongata or known as the medulla oblongata, let's say that it is the last brain structure in the caudal direction because after the medulla What comes next is the famous spinal cord.
Very well, then the scheme that I have accustomed you to, the brain divided into a forebrain called the prosencephalon, which in turn is subdivided by a more superior region, which is the telencephalon, is the cerebrum and a vesicle that embryologically developed a lower portion called the diencephalon. , very good, then we would have the midbrain, which is the mesencephalon alone, it does not have divisions; Finally, in the posterior brain, which is the rhombencephalon, in turn divided by an upper portion called the metencephalon and a final portion, which would be the myelencephalon. Incidentally, the only structure that makes up the brain is the medulla oblongata, which is precisely what it is.
What are we going to talk about today? So, as a diagram, you already know that the metencephalon, the most superior portion of the posterior brain, has or contains the pons anteriorly and the cerebellum posteriorly, while the myelencephalon, notice, alone contains that medulla oblongata or medulla oblongata as you call it. want to call; So the importance of this medulla oblongata is that first, being the most distal portion of the entire brain means that any communication, any communication without exception that wants to pass from the most superior brain to the spinal cord, has to go through the medulla oblongata, That is, the lessons generally when they occur in the medulla oblongata compromise many functions, too much, in addition there are the nuclei of the last four cranial nerves: the glossopharyngeal, the vagus, the accessory and the hypoglossal, so all the ascending sensory fibers that They come from the spinal cord and pass through there, all the descending fibers that are motor that come from the cortex or regions or other regions, let's say brain, also pass through the medulla oblongata, so imagine the importance of knowing the specific anatomy of this structure.
Very well, then we can say that the medulla oblongata is placed between the pons or annular protuberance that you can already find in the canal and the spinal cord below, that is, it is a structure that is practically between the two, it is interconnecting, very well, it is a structure that passes through the foramen magnum, what do I mean by it crosses the foramen magnum? We are not going to say that the medulla oblongata reaches the foramen magnum, that is a slightly erroneous concept, it is a concept that is no longer in vogue, it is a concept that is already known to be wrong, the medulla oblongata simply passes through the foramen occipital or foramen magnum, that is, it has an inferior portion that is small, yes, but it has that it is inserted inside the spinal canal and it is inserted inside the spinal canal and it is still the medulla oblongata. The eye has not become the spinal cord, Now I'll tell you what the cut-off point is between the medulla oblongata and the spinal cord, which is where we say students sometimes get confused the most, so I don't want them to forget that it passes through that foramen magnum and then it's going to have approximately, it's said.
two types of limits, it will have a nervous limit as such that is a limit that is a little imprecise, difficult, I am going to tell you about them and it will have an anatomical limit as such that is not nervous, it is anatomical that we can see from outside, in fact it is much easier to look for the anatomical limit than the nervous one, so let's see that in itself let's say that, of course here I drew the line a little long, if it is related then to the anterior arc of the atlas, that is , from C1 to the anterior portion of the occipital bone, what is called the basilar portion of the occipital bone, it will be in contact with all of that, be careful, do not get carried away by this line, I simply made it as a reference but it does not reach that far down how she wants to show that, then she tells herself that she had a shape of a truncated pyramid, in this pyramidal shape it has an upper base, that is, a pyramid that is upside down and the upper part is widened, it has a longitudinal axis that goes from bottom to top and from back to front. what does that mean? that the upper portion is a little more anterior than the posterior portion, in fact you see that it is not completely straight but rather oblique, you can see more or less an oblique type annulus, one thing you have to know, another important thing is that it is partly crossed by the beginning of the ependymal canal or duct and that it is the conduit that would take it to the spinal cord, which would continue the fourth ventricle with the spinal cord.
Okay, so one thing you have to know is that the upper limit is quite precise, it's easy to see, the upper limit is the continuous bulb groove, why continuous bulb? because they call this the medullooblongata or medulla oblongata or we also call this sulcus medullopontine for medullopontine sulcus, in this medullopontine sulcus it is quite important because there we are going to see the emergence of the sixth cranial nerve which is the abducens, remember that we are talking about the fifth that came out of the bridge itself then remember that the cranial nerves are in order, then the sixth which is the abductor of the eye, then the seventh which is the facial with its sensitive part and then we would have the eighth which is the vestibulo-cochlear nerve, then this medullopontine sulcus contains the apparent origin of these three cranial nerves 6, 7 and 8. Very well, the lower limit as I told you is a little imprecise, it is sometimes difficult to limit it, the nervous limit is said to be immediately superior to the emergence of the first fascicles of the C1 spinal nerve, so let's say this is the anterior roots of C1, so above it, which would more or less be this level, is the limit where I say up to there the spinal cord ends, up to here it ends and this coincides with the decussation of the pyramids that we are going to see there, in fact it is said that the spinal cord begins when the decussation of the pyramids occurs, this central structure that is uniting both pyramids that is the nervous limit as such, the anatomical limit does not tell us I like to take it so much because sometimes it doesn't correspond, why?
Because sometimes the spinal cord reaches a little lower or reaches a little higher, the anatomical limit that is taken is said to be the upper edge of the anterior arch of the atlas, that is, you draw a line that touches the anterior arch of the atlas, that is, of the c1 vertebra and the upper edge of the posterior arch and up to there you make the cutting point, from there up spinal cord, sorry oblong medulla and from there down spinal cord, however sometimes it is not C1 corresponds to the real limit because sometimes part of the medulla may remain a little lower and by drawing that imaginary line there you exclude, let's say, some nuclei that are within the medulla oblongata for example, then it is not better to talk about the nervous limit than of the anatomical limit as such. Let's see then the structures, see that it is very rich in structures, the anterior face, the lateral face, it has many grooves, many projections, so we are going to talk about each of these structures, but don't go away from the video [Music] it is very important that you subscribe to the channel below where you read that it says subscribe, click on it and well you are subscribed to the more than 240 anatomy videos that we have to date. So well, we continue talking about the let's say structures that are found inside the medulla oblongata, starting to talk about the anterior face and the lateral face, the first thing we are going to notice about the anterior face, we are going to try to go in order, it is the median sulcus.
anterior you will also see it with the name of anterior median fissure and that same anterior groove that the spinal cord has, see that it is the same one that continues upwards, that anterior median groove will end in a fossa that is blind, or That is, it doesn't lead anywhere and that is called blind foramen, okay? blind foramen. Very well, let's see that at the bottom there is the decussation of the pyramids, which is the place where the fibers of the path The pyramidal system begins to move from one side to the other in the famous deposition of the pyramids, which when you study the ascending and descending pathways of the central nervous system you will remember, so of this decussation that I am naming you right now, remember that this would practically be the adjacencies of the lower limit of the medulla oblongata and its separation with it in the spinal cord, very good, then on the sides the first projection, the first elevation that we are going to see is the bulbar pyramids, okay?
What is the first structure that we are going to find lateral to the midline after those bulbar pyramids we are going to see a groove, that groove is called the pre-olivary groove because I go ahead, this elevation that you see here we are going to call the inferior olive, it exists a nucleus that is there, which is the inferior olivary nucleus, that that nucleus, let's say that becomes prominent, pushes the white matter outwards and that is why we are going to see what happens with this prominence here, then the sulcus that remains in front of it, which is The one that separates it from the pyramid would be the preolivary groove; some authors also call it the lateral ventral groove. Okay, why is this groove important? because this groove is going to leave 10 to 12 fillets, which are what are going to originate the apparent origin of the twelfth cranial nerve, which is the hypoglossal nerve, I am now close to making the cranial pairs the real origins, apparent, the entire route of each one of the cranial nerves that have been asked for a lot but I want to finish with the brain part first, so don't forget the apparent origin of this nerve is precisely in that groove between the pyramid and the inferior olive.
So, well, I already told you about the inferior olive and we are going to notice that there is a pit above the olive at the level of the medullopontine sulcus. This would be it. If this pit is called the supraolivary pit, it will give rise to the seventh cranial nerve and the sensory nerves.
of the seventh cranial nerve, that is very important, very good, let's go now with this vision, don't be scared, look, this is the olive, this would be the pre-olivary groove that I told you just now, very good from here on down it is the spinal cord, no. I'm not talking about anything down here because it is the spinal cord, here you can see the root of C1 and the anterior and posterior roots, okay? So just as there is a groove in front of the olive that is the pre-olivary groove, there is a groove behind it that is the retroolivary groove, okay?
retro olivary groove, it immediately creates an area called the retro olivary zone, so here is something very important that entangles a lot when we study the medulla oblongata, which is the presence of the lateral dorsal sulcus, the lateral dorsal sulcus is not the same retro olivary sulcus, no is the same, the retro olivary is immediately behind the olive, the lateral dorsal sulcus is much more posterior and that lateral dorsal sulcus has the apparent origins of the ninth cranial nerve, which is the glossopharyngeal, of the tenth, which is the vagus, and of the root. cranial part of the accessory, remember that the accessory nerve has a spinal root which are these rootlets that you see here and this would be the cranial portion, now, many books talk about the apparent origin of these cranial nerves being from the retro olivary sulcus, yes, but others agree that it is the lateral dorsal sulcus, generally the books that say it is the retro olivary sulcus is because it does not recognize a lateral dorsal sulcus what happens is that you, here I open an important parenthesis that you know so that later no one says that the doctor was wrong or he told me this, what happens is that you look there and you really see the quite marked grooves and it seems very difficult to make a mistake, but when you see a live brain stem you will realize that it is not You see those grooves just as you see them there, you can't see them, you can hardly notice the grooves, in fact, I'm going to leave attached in the description of this video a link to a quite serious scientific article, you can see a serious university that says that the lateral dorsal sulcus does not exist, imagine then in this case that it would be wrong for me to say that the apparent origin of the glossopharyngeal, the vagus, the accessory is the lateral dorsal sulcus, they already did a dissection at 60, between 60 and 70 of the trunk encephalic, I don't remember and they said that there is no such sulcus, it is not really seen, this rootlet of these three cranial nerves emerge at a distance behind the retro olivary sulcus and that there are no sulcus, they simply come out of the brain stem and without an apparent sulcus that is forming it, So the question remains as to what the apparent origin of each of those three cranial nerves is, what it is not, is the retro olivary sulcus, it is a portion, an area that is behind this retro olivary sulcus, yes. They want to see it in this image in this way from before you will notice the apparent origin the glossopharyngeal is more superior, then in the tenth which is the vagus nerve and then the accessory that has its cranial root that comes from the medulla oblongata because the nucleus It is in the medulla oblongata and its spinal root that comes from the most superior spinal segments, now, if you see this view, the posterior face of the medulla oblongata, notice that the medulla oblongata has an upper half that is inserted as the floor of the fourth ventricle, you will also be able to find videos of the fourth ventricle within the channel, but it has a lower portion which is the one that we are going to study more or the one that we are going to study here that is outside the floor of the fourth ventricle, why Why didn't the upper half name them?
Because I explain the upper half on the floor of the fourth ventricle, then it would be to make a longer video and then repeat the same thing. In that lower half we are going to find the famous entrance of the ependymal duct, which is the one that continues, let's say with the ependymal conductor of the spinal cord, the upper half, as I told you, helps to form more or less the floor of the fourth ventricle, so on this posterior surface we first find a groove that is the same, it is the same groove in the spinal cord that is the posterior median sulcus, on the sides of the posterior median sulcus we find two prominences: the most medial of it is the gracile tubercle, which is a continuation of the gracile fasciculus that comes from the spinal cord, and the most lateral one is the cuneiform tubercle, the gracilis and the cuneiform, This cuneiform tubercle is important because this cuneiform tubercle is the one that you will later see that upwards gives rise to the famous restiform body, which is what will give rise to the inferior cerebellar peduncle. When you study cerebellum 3, when I talk about the cerebellar peduncles, you will see that the inferior cerebellar peduncle It is the one that connects the medulla oblongata with the cerebellum.
So you already know that it is more or less thanks to this rectiform body, so I remind you, posterior median sulcus, lateral to it the gracilis tubercle and lateral to it the cuneiform tubercle, the groove that is separating the gracilis from the cuneiform is the intermediate sulcus posterior, which is the one you see here, it is called the posterior intermediate sulcus and then we have the dorsolateral sulcus that we already saw on the lateral side, we are going to see it now in a lateral view, which is the one we had, let's say the confusion of whether it was there where the ninth, tenth and eleventh cranial nerves actually originated. So let's see this structure, which is, let's say, an elevation that is the trigeminal tubercle, in the nucleus, let's say, the trigeminal medullary nucleus makes this prominence and that's why it receives the name trigeminal tubercle, okay? Well here I point out the inferior cerebellar peduncle that I already told you that it originates thanks to the cuneiform tubercle that is to one side, so see here in this lateral view so that you can more or less continue this image with the previous view that would be the median sulcus posteriorly, the gracilis tubercle, cuneiform tubercle, posterior intermediate sulcus because it is the one that is separating the gracilis from the cuneiform, notice that then there we would have the dorsolateral sulcus, see that behind the dorsolateral sulcus is the trigeminal tubercle that I told you Just now a while ago, this would be the inferior cerebellar peduncle, these two that you see here, so if this is the dorsolateral sulcus, trigeminal tubercle, here would be the retro olivary sulcus, so always ask: ``doctor, what is this sulcus?
? `` This one that you see in the middle, well, that groove has nothing to do with the medulla oblongata, that is a groove that is a continuation of what they drew up there because it is a groove It is really from the spinal cord, if it is from the place where the roots are emerging, which would be the spinal portion of the spinal cord of the eleventh cranial nerve, which is the accessory nerve, it no longer has anything to do with the medulla oblongata and this one that you see here You already know it, which is what gives rise to the twelfth cranial nerve, which is the hypoglossal nerve, which was the pre olivary sulcus, okay?
