🥇 MÉDULA ESPINAL 2/4 - (Raíces Espinales) -Anatomía. ¡Explicación fácil!

Hello, hello, how are you? How are you? Welcome to a new anatomical video on this channel, easy anatomy by Juan José Sánchez.

Today I bring you the second installment of the anatomy of the spinal cord, remember that there are going to be four videos in total talking about the macro anatomy of the spinal cord, in the first video we talk about its external configuration, its internal configuration, the disposition of the white matter and the gray matter; Now in this second video we are going to dedicate it to the spinal roots in particular, do not confuse the spinal root with the spinal nerve itself, okay? We are going to talk only about these spinal roots, which, believe it or not, have a somewhat intricate anatomy and well, in the following videos we will talk in the third about the meninges that surround this cord and in the fourth we will talk about its vascularization, that is, , its irrigation and venous drainage; Apart from this, I am going to prepare a separate video for you, which is the vertebral venous plexus, a video that I owed you and that while doing the spinal venous drainage I realized that I had to complement it with that venous plexus, we are going to do that with a video apart not with the name of spinal cord. Well, without anything else to add, let's start talking about these spinal roots, remember that they are two groups of roots, anterior roots that each spinal nerve will have an anterior root and a posterior root, so the anterior roots for their part Let's see that they are motors.

It is the first thing you have to know, even though we are not going to talk about systematization here, you have to know that the anterior roots of each spinal nerve have motor information, that is, information that comes from the system. central nervous system, that's why they are called having efferent type fibers, okay? They come from the spinal cord, specifically what part of the spinal cord?

They emerge from the anterior horn of the spinal cord, remember that in the spinal cord video I explained that these anterior roots emerged through a groove called the anterolateral groove and that it was precisely the place where the lateral white cord and the anterior white cord were limited, that is very important. Then we will have the posterior roots that are the complete opposite of the previous ones, why? Because these posterior roots come out of the posterior horn, see that it is the counterpart of the anterior horn that originated the previous ones and these posterior roots bring sensitive information, that is, information that reaches the spinal cord with information, which is why it is called that its fibers are of the afferent type, so efferent is the one that they bring or those that come out through the anterior root, efferent or sensitive is the one that arrives through the posterior root, you see that each root is made up of a group of rootlets.

let's say more and more divergent when they get closer to the cord and when they move away from the cord as they get closer to the spinal nerve itself as such they become more convergent between them, that is important for you to know, these posterior roots are Your part, remember that I told you that they came out of a groove called the lateral dorsal groove, which, by the way, was the groove that delimited the lateral white cord from the posterior white cord, very good, now let's talk about what these are like. origins of these spinal roots, remember then what I told you since each root as such, which this would be, is made up of fibers, rootlets that are converging as they move further and further away from the spinal cord to form a single root, okay? Here we see it a little better between a cross section at the thoracic level, I know it is thoracic because you see the lungs here, I see the thoracic aorta too, we are going to see that the origin of each let's say spinal root varies according to the segment in which it is located.

find, for example, we are going to see the roots that are typical of the upper cervical nerves and have fibers that are quite thin and apart from the fact that the fibers are thin, they are quite separated from each other, it is said that they have the shape of an open fan, so Why are they thin fibers? well because the upper cervical types between C1 to C4 are really going to form a plexus in the cervical plexus that is not so rich in nerve fibers, Therefore, it does not need as many thick fillets as such. However, when we see the fibers of the lower cervical type than those of C5, C6, C7 and C8, we see that the fibers are rather thicker, more voluminous and also the fan is quite closed.

because it is a greater number of fibers and this is because these lower cervical type fibers are first typical of cervical intumescence, okay? Remember that we talked about it in the first video about the spinal cord, the second is because it is going to form the brachial plexus, the brachial plexus is very rich in nerve fibers and therefore needs a greater contribution from that spinal cord, something important that you have What to know is that each spinal nerve that is made up of an anterior and posterior root will ultimately have mixed information, will have the nerve already constituted, will have motor fibers or have sensory fibers and will even have autonomic fibers because well In the autonomic nervous system it enters between the spinal nerves to distribute with them in part in certain segments. We then continue descending, we already know what the cervical type fibers are like, we go to the recurrent thoracic type fibers, the thoracic type fiber is going to form the intercostal nerves and these intercostal nerves do not have great innervation, they generally innervate the joints part of the bone, of the muscles of the thorax and part of the back therefore they do not need a large contribution of fibers, we will see that the fibers are quite thin and in addition they are very few, very spaced between them, those are the thoracic type fibers.

When we see the lumbar type fibers, which are the last fibers that emerge from the spinal cord itself, see how the conus medullaris is already forming here and finally the filum terminale, these lumbar type fibers are quite thick and quite tight. among them and it is typical then of lumbosacral intumescence. What is this due to?

Well, you have to know what these fibers are at the sacral level, at the lumbar level, well at the lumbar level, sorry, it will form the lumbar plexus, the sacral plexus, so together it is called the lumbosacral plexus, so this is quite a plexus. rich in fibers it really had quite a few fibers emerging from it and therefore there must be more bulk in those roots. Very well, then we are going to continue talking about the spinal nerves as such, already constituted, we already talked about the roots, but first don't go away from the video.

[Music] ok, subscribe to the channel below where you see that it says subscribe, click on it and well you are subscribed to the more than 252 anatomical videos and we continue making, if there is any video that you can't find on the channel, write it to me in the comments, Don't forget to also write to me where in the world you see me and what university because sometimes the comments don't really know where and from what university they are seeing me and well, that way I learn a little more about who my audience is. We had then been talking about the spinal nerves, the spinal nerves or fast nerves, rachis means spinal cord, well it has to do with spinal cord, they are nerves that emerge from the spinal cord but are no longer part of the central nervous system, remember that The central nervous system was the spinal cord, then what is emerging from it becomes the peripheral nervous system, there are 31 pairs, yes, counted from the first cervical to the coccyx, we will see that each one emerges at each side of the spinal column and I had already told them that they had mixed information, that is, they have motor information that is attracted to the anterior root, sensory information that comes from the posterior root and autonomic information that the autonomic nervous system sometimes uses. As a way to convey your information, let's see in this diagram I put it a little bit backwards so that you wouldn't get confused, we see well sagittal we see in colors including the segments, then we are going to see that the cervical nerves are 8, we say that there are 8 cervical pairs, that is, there are many cervical nerves, if you have already studied the spinal column, which is logical, the logical thing is that you master the spinal column, regardless of whether you study in my videos or from where you study it, you have to master it to understand the spinal cord.

, you will remember that they are nothing more seven cervical vertebrae but eight nerves, so you will see that sometimes the C8 nerve is named but the C8 vertebra does not exist, the important thing is not to be confused, so these cervical nerves have the characteristic that they emerge above the vertebra that corresponds in number, so that if it is the C1 vertebra the nerve that comes out above then it will be the one that corresponds in number, which is the C1 nerve, if it is the C3 vertebra, the nerve that is above is the c3 nerve or third cervical nerve, is that important, what is happening? The C8 nerve is not going to emerge above the C8 vertebra because there is no C8 vertebra. What is going to happen to the C8 nerve?

We are going to go above the one below where the number corresponds to it and the one that corresponds to it and the one that would be below would be the D1 vertebra, which is the first dorsal vertebra or t1, which is the first thoracic vertebra, however you want to say it, then c8 would come out above d1 but that will cause a change in the conformation of the following spinal roots. Why? Those in blue are the thoracic nerves, also called dorsal, which are 12 pairs, the most numerous in number.

What is happening with these thoracic nerves? That they are not going to correspond the same as the cervical ones, why is that what is going to happen? The first dorsal or thoracic nerve should come out.

If you continue with the sequence of the cervical nerves, it should come out above the D1 vertebra, but we find that what comes out above the D1 vertebra is the C8 nerve, so two cannot come out. nerves in the same place, then they only have to emerge below the D1 vertebra, so that from the first dorsal nerve all the way down, they will emerge below the vertebra that corresponds to them in numbers, ok? then the first dorsal nerve comes out below D1, which is the same, that is, above d2, the second dorsal nerve comes out below d2, which is the same, that is, above the d3 vertebra, and so on from there downwards.

and that happens precisely due to the presence of the c8 nerve that deconfigures the entire spinal cord from there on down, it is important that you never forget that formula. Then we have five lumbar pairs until now we have eight, twelve, we have twenty-five, 25, then we would have five sacral pairs and some in this case we have thirty nerve then and a coccygeal pair, sometimes they can be two coccygeals but most of the time It is one, if you add all that up it will give you 31 pairs of spinal nerves, that is very important. What is the direction and path of these spinal nerves?

Notice the anterior and posterior roots of each spinal segment join to form a single spinal nerve on each side, remember that this is a transverse section so once it joins they will form a trunk, which trunk is called the spinal nerve itself, while they are not joined they are still roots of the spinal nerves, where will they come out? They expect that the spinal cord is inside the vertebral canal so that the vertebral roots are inside the vertebral canal as well, they have to come out through a hole called the intervertebral foramen or foramen of conjunction, which we talk about very well when we talk about the videos. spine, okay?

Once the spinal nerve is formed, each spinal nerve will have a particular path for each nerve that I am not going to explain in this video, because in this one we are going to talk about nothing more than the beginning. So a very characteristic thing that the posterior root has is that it has a bulge, that bulge is called the spinal ganglion and it has a lot to do with the sensory function, a relay station of the sensory pathway but it is characteristic of the posterior root, of In fact, sometimes we can recognize if it is the anterior or posterior root by the presence of the ganglion, that bulge is a way to recognize it. Very well, notice, then there is a discrepancy between the spinal segments, it is assumed that the spinal cord is made up of segments that we had talked about in the previous video but we are going to see that the nerve that comes out of each segment, each segment is supposed to have a nerve , It will not always correspond to the place from which it comes out, that is, he explained to them, for example, look at this thoracic segment, the last one, look at the D12 nerve when it emerges from the spinal cord, as is the D12 vertebra, it will then come out from below.

from the D12 vertebra, as is the D12 nerve, sorry, it comes out below the D12 vertebra, but see that where it comes from is very below the segment, it does not correspond; then it is a rule that says or shows that the cervical root of C1, which is ascending, is the one that really goes upwards, it means that the C1 cervical segment of the cord is below the emergence of the nerve root c1 Yes, they more or less understand, right? If you see the cervical root of c2 and c3 they are horizontal, they are at the same level of the segment from which they come out, there is no problem, but from there on down you begin to see that they are becoming more and more oblique, more oblique, oblique, more oblique, more oblique and I explained that this was due to the fact that the spinal canal lengthens and the spinal cord is practically not the same size, the spinal cord also grows but the growth of the spinal canal is much greater, so it goes away stretching, lengthening downwards, see the dural sac how it lengthens and really as you can see in the last nerves that are emerging, they are very below, very oblique to the segment from which they are originating very below. Now when you see those of L4 and L5, which are these last two places, and you see all the ones that emerge from the medullary conus, you see that they are no longer oblique, rather they are vertical and they are the ones that make up my ponytail, which are what make up the famous cauda equina or horse's tail, we are going to see it a little later, here we see anyway in this section we see the terminal cone at the level between the intervertebral disc of L1 and L2 and we see that these fibers To say a beard, they begin to surround, looking like a horse's tail, the entire filum terminale and also surround the terminal cone, remember that the filum terminale was the central nerve that we saw here.

How is this ponytail going to be formed? It is said that it is made up of the last 10 spinal roots on each side, this is from the L2 nerve, so you count L2, L3, L4 and L5 you will see 4, count the four roots, the five sacral roots plus four that we had nine, plus the coccygeal nerve would then be ten, the last ten spinal roots as I just told you, anyway in this cross section this is the terminal cone and notice this as surrounded by pia madre, on one side we see the bit of rootlets that those are the ones that make up the famous filum terminale, of course it looks quite disordered there but really the fibers of the filum terminale see that they are quite ordered, we see that from the lateral to the medial, that is, the more lateral the fiber means that it is It remains in a slightly more superior segment, while the fibers become more medial, notice that they are the ones that go to the lower segments, that is very important so that the last coccygeus, which would be these two most medial ones, are the ones that go found closer to the midline because they are the ones that have to travel the longest. Now we are going to talk about spinal cord topography.

Also note a concept that I want you to understand and that is what we call the correspondence of the spinal segment with the spinous process. It is what we call spinal cord topography. What does this mean?

What I have been saying for a while now is that the spinal segment does not correspond to the vertebra where the nerve that derives from that segment is emerging. Right now I will more or less explain it to you, but now I am going to tell you exactly what the rule of spinal vertebro topography says, We see here in the L1 vertebra, the spinous process of L1, which is what we take into account for the rule, the spinous position of each vertebra, I know it is L1 because you count here L5, L4, L3, L2 and L1. start from the bottom up, then you see that in front of the L1 vertebra the L1 segment should be the logical thing, but look at the L1 segment above tucked inside the dorsal column and see that what is in front of the L1 vertebra They are the sacral and coccygeal spinal segments, that is, practically what is inside the terminal cone in the L1 vertebra.

If we see the t12 thoracic vertebra, which would be the one immediately above L1, it corresponds to the L5 spinal segment, you can see it there. spinal segment L5, here they are talking about the spinal segment, that is, its correspondence with the column as such, well, if we see the T11 vertebra, the spinous position T11 corresponds to the spinal segment L3, L4, do not confuse vertebrae with segment spinal cord and do not confuse the spinal segment with the spinal nerve, they are three totally different things, then we have the spinous process of the D10 vertebra, see that it corresponds to the spinal segments L1 and L2, then we have the lower thoracic vertebrae, which are the spinous processes of T7, T8 and T9. So see that the rule says that in those thoracic vertebrae from T7 to T9 3 are added.

What does that mean? That in front of T7 has to be more or less, more or less of course the spinal segment L10 because I am adding 3, L10 no sorry, D10 what does that mean? that in the thoracic vertebra t8, which would be this, 3 should be added to it, segment D11 should be and that segment D12 should be in t9, you take 3 to 9 and you are going to say that the spinal segment is located there.

In the most superior topographic vertebra, that is, from T1 to T6 it is not added in three, but two are added so that in front of t1 the third spinal segment should be because I am adding two to it and in front of t6 There should be spinal segment 8, which is D8, since the one that corresponds to the t6 vertebra. Lastly, look at the cervical vertebrae. Here, what you have to do is add 1, so you see that in front of the c1 vertebra is located the second spinal segment, in front of c2 the third and so on until reaching the seventh cervical, it is important that you know this.

Ok, to finish, let's talk about the characteristics of these roots and these spinal nerves depending on which portion of the spinal canal they occupy. Remember that the spinal cord only occupies the cervical, thoracic and upper lumbar portions because it ends between L1 and L2, that is, they occupy those portions of the vertebral canal, I mean, you already know that the lower lumbar portion and the sacral portion are occupied by the caude equina and the filum terminale, that is important; Now for a nerve to leave the spinal cord it has to cross all its membranes, which are the meninges, which we will talk about in the next video, but here I have to show you with respect to the spinal roots, at the level of the dural sac. What does the dural sac mean?

? The dural sac is everything that is inside this envelope on the outside that is the dura mater, that is, everything that is here, see that the anterior root, which is this, once they emerge from the anterolateral sulcus, will continue laterally and posteriorly or towards posterolateral as I put here, for its part the posterior root, I know that this is the posterior one because the dilation it is giving, the posterior root when it is inside the dural sac that emerges through the dorsolateral sulcus is directed anteriorly and laterally , towards lateral, that is, towards anterolateral, important, the anterior towards posterior and the posterior towards anterior, at this level they continue to be enveloped by the same pia mater which is this membrane that is covering the spinal cord; So at that level it is surrounded by nothing more than the pia mater, remember that this space that is here between the pia mater and the arachnoid is the subarachnoid space, so once they always look to the side they pierce the arachnoid, see how that are perforating the arachnoid, anyway here we can see the arachnoid in blue, in red the pia mater and here the pia mater wraps around the spinal nerve when it is at the request of the subarachnoid space which is this blue, what you see Here in green is the dural membrane, that is, the dura mater as such, notice that once it is looking for the external part, it finishes passing to the arachnoid and begins to perforate this green membrane that is the dura mater, then each spinal root is going to pierce the dura mater through an independent hole, that is, each hole allows a single nerve to pass through as such, at this level it is enveloped by both the pia mater and the arachnoid and in turn begins to gain the envelope of the dura mater, it has the triple envelope At this level, pious mother, arachnoid and now also dura madre, when it comes out of the rural sac we are going to see that these roots are directed through this space that is the intervertebral foramen, okay? conjunction hole and both roots join and form the spinal nerve itself but this is formed outside the dural sac, in order for them to finish coming out they have to go through this operculum, which is this ligament called the fibrous operculum, we see it from here We see that the union of the roots is done very outside the dural sac, notice that it is quite outside and in addition they do it after they leave the intervertebral foramen, this is important so that you can see here you see how the roots are surrounded by the arachnoid that It is transparent and then wrapped by the hard mother and finishes making another wrap that in fact continues to wrap around the entire spinal nerve because it practically fuses with the perineurium, one thing that I took advantage of in this image and I show you is the dentate ligament, this The dentate ligament is found from above in the first medullary segments and ends more or less at the level of t12 and l1.

It will always be interposed between the anterior root and the posterior root. It is a ligament that, let's say, separates the anterior root and posterior of each of the nerves and we always see it inside the meningeal membranes. Let's see here in a view from the sides of the foramen of conjunction and there we see how each spinal nerve comes out as such and then well I came to make its corresponding subdivisions, finishing well the horse's tail that you already know and is already at the bottom of the dural sac of that cauda equina, it is a set of fibers formed by the last 10 spinal roots on each side and it surrounds the central cord which is the filum terminale, here we can see how the filum terminale reaches the first coccygeal vertebra, ok ?