Hello hello! My dear anatomy students, welcome to a new anatomical video on this channel, Easy Anatomy, by Juan José Sánchez. Today we are going to talk about the first installment of four on the anatomy of the spinal cord.
In this first video, we will address the internal and external configuration of the spinal cord. The spinal cord is a somewhat long topic, that is why in the second video we will talk about the arrangement of the spinal roots of each segment of the cord. In a third video of spinal cord 3, we will talk about how the measurements are arranged, the envelopes at the spinal level, nothing more.
And finally, in the last spinal cord video 4, we will touch on the topic of spinal cord vascularization. In these installments, we will only talk about large anatomy, macroscopic anatomy now, talk about the tracts, talk about the fascicles of the fibers that carry that already leads to other topics that are the systematization topics that we will address when we finish all the neuroanatomy content macroscopic as such. Very well, then without anything else to add, we begin by first talking about the generalities of this spinal cord.
Remember that the spinal cord is part of the central nervous system. In general terms of the nervous system, we talk about the central nervous system being divided into two portions: an upper or cranial portion that is within the cranial vault, which is the brain, and a lower portion that is inside the vertebral canal, which is spinal cord. So the spinal cord can be said to be a continuation of the brain stem, it is a continuation of the brain in a thick set of fibers.
Many students when they begin to study anatomy greatly confuse the spinal cord with the bone marrow, which is totally different. Bone marrow is a hematopoietic, blood cell-forming tissue found inside bones, particularly long bones and some flat bones. While the spinal cord was already a nervous tissue found within the spinal canal.
And so they want to understand that the spinal canal you have to look for my spinal column videos in which we address the vertebrae of the spine as such and explain more what this spinal canal is like. The fact is that the spinal cord is not completely isolated but rather has that bone protection that is quite important mechanical protection. Very good, now the spinal cord is surrounded by a set of membranes that is what we call the meninges.
These membranes, meninges, which are the same or very similar to those found in the brain, surround the spinal cord in all its thickness and which we will talk about in a third installment of the spinal cord. So, the first envelope that it will have is the meninges, and then it has the entire, let's say, bone structure of the vertebral canal that ends up protecting it from a mechanical point of view. Look at this previous vision, here see the spinal cord in the background and see how it is surrounded by a set of membranes that, well, as I say, we will not address in this video.
It is so that you can see how it surrounds them and we can see how the famous spinal nerves or spinal nerves emerge in the spinal cord, which are all those nerves that perhaps you have already studied that deform the plexus, which is the cervical plexus, brachial plexus, lumbar plexus, The intercostal nerves, which we give names according to the segment, if they are cervical, we called them c1, c2 and the thorax and we called them t1, t2 and lumbar L1, L2, etc. It is so that they understand that these nerves then emerge from the spinal cord. Very well, when we see the vertebral column and the spinal cord in a sagittal section, we see that the spinal cord is not a completely vertical structure but rather has a series of curvatures, curvatures that are the same or that coincide, so to speak, with the curvatures own of the spinal column.
If you already know the spinal canal, which I recommend that you master so that you can understand the spinal cord, you will remember that at the cervical level there was a concavity towards posterior or what is the same as saying one concavity towards anterior, then obviously the spinal cord spinal at that cervical level is also going to be a posterior concavity. When we get to the thoracic segment of the spinal cord we see that it makes a large convexity towards anterior or convexity towards posterior as you want to say and finally in the last portion let's say of the spinal cord that remains at the lumbar level we see that it makes a small posterior concavity because the vertebral column can be seen to be quite concave posteriorly at that level. It is very important to know, see here again a posterior cervical concavity with a dorsal anterior cavity and finally the final segment of the cord at the lumbar level makes a posterior concavity.
Okay, what are the limits going to be in the spinal cord, we're going to have an upper limit okay and a lower limit. The upper limit is the one that occurs when it continues with the medulla oblongata with medulla oblongata, in the channel to the medulla oblongata video, that is, the part of the spinal cord that connects directly to the brain stem and thus to the brain as such. It is through the medulla oblongata ok what is this let's say this bulb that bulge that forms at the end of this nervous tract.
Now, as we establish the cut-off point, up to where I say it is the spinal cord and where the medulla oblongata begins, it is really quite difficult to establish the limit as such, at least from an anatomical point of view it is quite complicated. We speak of a nervous limit which is the limit as such of the nervous structure of the nervous cylinder and it is said that this limit is immediately above the recusal of the pyramids which is this structure that you mentioned in the previous part but it is also said which is a point that is exactly above the emergence of the first cervical nerve, which is this one that you left here, which is the c1 nerve, so above c1 it is said that from there up the medulla oblongata and from there down it is the spinal cord spinal that is the nervous limit. There is a bony limit that is a conventional limit, however it is not very convenient for us to learn the bony limit or take it as a reference because not always, if some people have this part of the spinal canal a little narrower and the medulla oblongata is actually a little below.
But the limit we take, let's say from a bone anatomical point of view, is an imaginary line that passes over the c1 vertebra of the anterior and posterior arch of c1, which is the atlas vertebra, ok, which would also pass over the apophysis odontoid of the c2 vertebra. That is the bony limit as such that then separates the medulla oblongata above from the spinal cord below. Regarding the lower limit, it is a little easier to elucidate.
You see that the spinal cord narrows as it becomes lower until it immediately reaches the level of the intervertebral disc that separates the L1 vertebra from the L2 vertebra. See that this is D12 because I see that it grabs the twelfth rib, then this one L1 L2 see the intervertebral space where the disc is between both vertebrae until there I say that it reaches the spinal cord in a structure that is narrowing called the conus medullaris that It is the lower portion, as we are going to see now, of the marrow. There is not much difference there, what is happening?
There is a central cord, I don't know if you can see it here, it is precisely the one that is in the center in the entire center, which is the filum terminale, it is a continuation of the spinal cord, that filum terminale or through the filum terminale, see there He marked them reaching the base of the coccyx, ok, to the base of the coccyx specifically at the level of the Co1 vertebra, which is the first coccygeal or the second coccygeal, although most say in the Co2 vertebra and that it is the second coccygeal, so well Through the filum terminale it can be said that this extension of the spinal cord reaches the Co1 or Co2 vertebra. Now, I bring this to you so that you can see that the level at which the spinal cord reaches is a little different as the organism grows and develops. Notice here that an eight-week fetus, like the spinal cord, covers the entire vertebral canal and goes into the sacral canal.
See how it reaches the end almost to the tip of the coccyx, and at 24 weeks, see how the level begins to rise. these 24 weeks already It is almost at the level of the first sacral vertebra, in the newborn, see how it reaches more or less at the level of the L3 vertebra, see the conus medullaris point, and in the adult, see how it reaches the intervertebral space between L1 and L2. is this due?
This is not because the spinal cord shrinks but because the spinal column itself begins to increase in size and therefore the cord becomes smaller and smaller with respect to the stretching of the spinal canal, so it is important to know. So now we are going to talk about the external morphology of the spinal cord, then we will talk about the internal morphology but first do not leave the video [Music] very important that you subscribe to the channel below where you see that it says subscribe, click on it and you are subscribed to the more than 250 anatomical videos found therein. We had then been talking about the external morphology, we see that it has a fairly long cylindrical shape, okay?
In this horizontal section we can see that, well, it is not really a perfect circle but rather it is a little flattened in an anteroposterior sense, so that in a lateral sense it is a little wider, that is, it is longer in width than from anteroposterior to That's what I mean. We are going to see that its size, its thickness is not uniform, but well, here we will add the structures of the brain stem, we see how in the uppermost portion it makes a bulge that we have called cervical intumescence and when it is ending at the level The lumbar spine makes another bulge that we call lumbar intumescence, if they are the two large bulges that the spinal cord has. Here in this section, well this is pasted here because this tip is the filum terminale precisely, well, on average, well it is said that the spinal cord measures 45 centimeters, remember that it reaches the level between L1 and L2 all of this that you see It is an extension of the nerve that we are going to see right now, which is called the famous horse's tail, but the cord as such that the bulge in the cylinder reaches the vicinity of L1 and L2.
So we are going to study six large portions of this spinal cord, its most superior portion called precisely that superior portion, it goes more or less obviously you will see that it will not always correspond to the image, it is an image taken from the Latarjet, it goes more or less from the anterior arch from the C1 vertebra to the anterior arch of the C3 vertebra, important because you will see that here it is separated into a segment. I don't know if you can see. These are called spinal segments or they also call it myelomeres, so we are going to see this upper portion.
where the myelomers originate and give rise to the spinal roots from C1 to C3, precisely which make up the majority of the cervical plexus. Then we continue with the second portion, which is precisely the most superior bulge that I showed you, we are going to call that second portion the cervical intumescence and here it is more or less marked in red. It is cervical intumescence, well, that cervical intumescence will go from the vertebra c3 more or less until the third thoracic vertebra, which is the D3 vertebra, however, in this image it more or less reaches the middle of D1, D2 at most, but that is what the theory says and what I always tell you, the theory kills to whatever is above what the atlas shows.
This cervical intumescence will then originate the c4 nerve, which is part of the cervical plexus, it is the last nerve of the cervical plexus, and all the roots of the brachial plexus, which is from c5 to c8, including the first dorsal vertebra, which is the D1 vertebra. okay? that is cervical intumescence.
Then we see the thoracic portion, which is the longest portion. It is worth highlighting here that they more or less put it in yellow. It will then go from the D3 vertebra because that is where the cervical intumescence ends to the vicinity of the D9, D10 vertebra.
or less, OK? then this thoracic portion originates the 11 intercostal nerves as well as originates the twelfth intercostal nerve, which for anatomy purposes is not called the intercostal nerve but rather the subcostal nerve, that is the famous thoracic portion. Then we have lumbosacral intumescence, which is the most inferior bulge that I showed you, This lumbosacral intumescence goes from the D9 or D10 vertebra to the L2 vertebra, more or less there is the L1 vertebra, L2 vertebra to put it more not so classically L2 and this lumbosacral intumescence is what will then originate the roots that go to the lumbar plexus and for the sacral plexus.
We will have then, the last portion of the spinal cord as such is the conus medullaris, we will see that it is the tip of the lumbosacral intumescence, it is located in front of the L2 vertebra. What is L2 here? Well, we count from bottom to top L5, L4, L3 and L2.
See how the tip is at the level of L2, obviously this is that way because here they put those segments of the cone as a slightly darker blue. But it is actually the final part that is located right in front of L2 and it will give rise to the sacral roots and the coccygeal roots. It is important that you see that the conus medullaris is surrounded by a group of nerves that together form the caude equina or horse's tail.
Finally, remember then the filum terminale which is the one that comes out from the tip of that medullary cone downwards, that filum terminale has two large portions, it has a shape well let's go in the order of the slides it has a threadlike appearance, They have a, let's say, circular appearance that becomes pointed as it reaches its end. They are born at the vertex of the medullary conus, as you can see above, a central structure that has two portions, one portion that is always surrounded by pine cone. mother that is inside the dural sac until it reaches the tip of the dural sac.
This is what I am showing you here, up to here it reaches the tip of the dural sac and from there that pial portion ends, pial because it comes from the pia mater, it is wrapped by the pia mater and the extra-dural or drural portion of the terminal filum begins. Why is it called that? because from there to below it is only enveloped by dura mater, then the next upper part that is inside the dural sac is enveloped by pia mater and the external portion that is outside the dura mater is enveloped by dura mater and through that dura mater envelope it reaches then to the base of the tailbone.
This would roughly be what we call the external anatomy, notice here this is the conus medullaris, all these roots that you see on the sides are the caude equina or filum terminale and here we can see how the conus medullaris is surrounded by the pia mater membrane of the internal meninges and well, that cone, as it continues with the filum terminale, will also be enveloped by the same pia mater. We are going to move on to the configuration and a little closer to the external one and then we finish with the internal configuration. This external configuration we have to study in a horizontal section.
We are going to study three large faces, an anterior face, a posterior face and two lateral faces, the The anterior is different from the posterior because we see that large fissure, we see that the posterior face has a mid-level groove but it is not that gap, it is not the fissure that we do see on the anterior face, so the first thing we are going to find is the median fissure. anterior also called the anterior median sulcus along the entire midline to the sides we find the anterolateral sulcus, important because that anterolateral sulcus is where the anterior roots of the spinal nerves will emerge. Notice here we have the anterior median fissure or anterior median sulcus and we see here the anterolateral sulcus and we see that from this anterolateral sulcus is where the anterior roots that make up each spinal nerve emerge.
Look at the uppermost part, almost reaching the medulla oblongata, we find the famous pyramidal decussation. Because? Because this portion that I have left here between, let's say, the anterior median sulcus and the anterolateral sulcus are called the pyramids.
So, that is why this union of the pyramids is called the pyramidal decussation. If we don't go to the posterior surface, which would be this one here, remember we see a groove that was called the posterior median groove that corresponds, let's say sagittally, to the anterior median fissure. We are going to see that this posterior median sulcus heads anteriorly.
or into the spinal cord through a septum called the posterior median septum. If we do not see it in the anterior part, towards the sides we find the posterolateral sulcus and between the posterolateral sulcus and the posterior median sulcus, here we see a medial sulcus crossed, we then call it the posterior intermediate sulcus, I repeat, this would be the posterolateral sulcus and this is the posterior intermediate sulcus. We find this posterior intermediate sulcus up to the level of the second thoracic vertebra, that is, D2, from there on down there is no posterior intermediate sulcus in the spinal cord.
Let's see that this posterior intermediate sulcus separates this entire white region of the spinal cord into two large fascicles: a medial one called the gracile fasciculus and a lateral one called the cuneiform fasciculus, ok, let's see that at the level of that posterior lateral sulcus the posterior roots of the spinal nerves emerge . So see that the anterior roots are from the anterolateral sulcus and the posterior roots are from the posterolateral sulcus. Okay here we see it here, in this posterior view we see then the posterior median sulcus, we see the posterolateral sulcus, this one here in the middle of the two is the posterior intermediate sulcus and I would have cords or fascicles left, the most medial one is the gracilis and the most lateral the cuneatus or cuneiform.
The lateral face is that face that will be included between the dorsolateral sulcus, which would be this or posterolateral, which is the same, and the anterolateral sulcus, which would be this one in front. This entire face that I have left here would be the lateral face, a face that is free of grooves as such, it would be this entire area that you denote between the posterolateral and the anterolateral. We now move on to the internal configuration.
You see, the internal configuration in the spinal cord is the complete opposite of the external configuration that we had in the brain. In the brain the gray matter was peripheral and in the center we obtained white matter. In the spinal cord, the gray matter is central and the white matter is peripheral.
Well, it is completely the other way around, the substance and here it is in the center of the marrow, it is very important that you know it. So I told you this, which is that the spinal cord is, let's say, composed of segments called metameric segments or simply myelomers, these myelomers are what give rise to the spinal roots as such or the spinal nerves. Let's start by talking first about the arrangement of the gray matter and you see the shape.
The gray matter is characteristically h-shaped because it has lateral concavities, an h-shaped. So when you join, let's say, each spinal segment, each geometric segment, you find that all the anterior gray substances coincide, the posterior one coincides, the middle one coincides, and columns are formed that go along the entire spinal cord. So basically we are going to see that around the central duct, which is this small hole that you see in the center, is arranged in three large columns of gray matter: One will load backwards, which would be the posterior column, remembering that the column is everything all at once.
from top to bottom. Then a face forward which is the anterior column and one that is between the two that is the intermediate column, of course we do not see this intermediate column in all regular ones that is why here, for example, we do not see it and I use this cut at the thoracic level and here we do see a column between the posterior and the anterior called the intermediate column. There is only an intermediate column at the level of the vertebrae, at the level of the thoracic column, I mean very well.
Let's talk then about what the antlers are. Well, these previous extensions that we are going to see in the horizontal cuts, the columns are the unions of all the antlers of all the segments. Antlers are just what you see when you make a horizontal cut or a cross cut.
Let's talk first about the anterior antler, remember that this is previous because I see the white fissure, the gap, the image is the opposite of what I have been teaching, but when I see the fissure I position myself and I know that this is previous. The anterior horn is also recognized because it is much more voluminous than the posterior horn. You see that it is quite wide and has a quite irregular contour.
Separately, see that it is directed anteriorly and laterally and we are going to see that the fibers that come out of it cross obliquely to the white matter and originate the anterior roots of each spinal nerve. Well? , anterior root of each spinal level.
When we look at the posterior horns we see that the posterior horn is much thinner than the anterior horn. Besides, it doesn't have that irregular route. We are going to see that its fibers cross obliquely posteriorly and laterally to the white matter and emerge from it in the posterior roots of the spinal nerves.
However, you see that the emergence of the anterior roots is simple, they emerge and the posterior ones have a set of areas that we are going to study. We are going to see that the area that it crosses, which is this one that is dotted here, is an area that is in the white matter, specifically called the dorsolateral tract, they also call it Lissauer's zone or dorsolateral tract. Then this posterior horn passes through this dorsolateral tract, we are going to see that the first portion of the spinal root and as such it is lighter, it is clearer and of a slightly softer consistency than the rest, that is why we call it the gelatinous substance or of Rolando.
Then it continues with an extension to the emergence of the spinal nerve itself, which is the marginal nucleus, also called Walter's nucleus, which is very important. Passing the lateral horn, well we looked for a thoracic cut because I explained to them that there was only an intermediate column at the thoracic level and that intermediate column when we study it separated like this is what makes up the lateral horn in two ways. Let's look for an approach here, see it there as a different cord.
Well, this lateral horn that is located between the anterior horn and the posterior horn is very important because it contains the nuclei of the autonomic system. In fact, that is where the sympathetic information is, especially the sympathetic information that arises at the level of the spine or the thoracic spinal cord, very well. We then continue talking about this gray substance, we are going to see that finally the anterior horns are joined by an anterior gray commissure and is in front of the central canal and is separated from the outside by the anterior white commissure.
So, this would be the anterior white commissure and there is the anterior gray commissure, while posteriorly we also have a posterior crease commissure, it is behind the central canal, it is less thick, see how wide the column is the anterior gray commissure. Then, the gray posterior commissure joins both posterior horns behind the central canal and this separated the outside by the posterior cord, there is no white posterior commissure, just as there is a white anterior commissure. The white matter, for its part, remember that it surrounds the gray matter is peripheral and its thickness is not different in all spinal segments.
Let's see that at the cervical level it is quite thick but as it descends the amount of white matter begins to decrease. In it we study cords, let's first look at the previous cords. These anterior cords are between the anterolateral sulcus, see where the nerve emerges in the anterior stripe of each spinal nerve and the anterior median fissure.
So you would have a right anterior cord, a left anterior cord and both cords join through the anterior white commissure that lies behind the anterior median fissure. Well, as for the back cord, well, that's all I have left behind. In the posterior commissure, it will be between the posterolateral dorsolateral sulcus, where the posterior roots of the spinal nerves emerge, and the posterior median septum.
This central septum, then, that posterior cord is what contains me, then, medially to the gracilis fasciculus and then the cuneate fasciculus a little more lateral. The lateral cord, for its part, is the one in the anterolateral sulcus, which would be this one, and the posterolateral sulcus, which would be this one, where the posterior roots leave me. Finally, we then talk about the central duct, called central duct of the spinal cord or duct of the appendix or appendymal duct, it is called that because, well, it is covered by ependymal membrane.
It is a continuation of the cerebral ventricles, it runs along the entire spinal cord from its beginning to the end. Now, towards the top, we see that it is a continuation of the fourth ventricle from the lower angle of the fourth ventricle. If you have already studied the 4th ventricle, you will remember what I am telling you.
While in the most final part, it ends in a dilation at the level of the filum terminale and does not even end at the level of the conus medullaris but at the level of the filum terminale. This dilation that occurs here is called the terminal ventricle, which is a blind area and no longer continues with the rest of the structures , let's say, through which the cerebrospinal fluid flows. It goes without saying that the cerebrospinal fluid flows through this central conduit of the spinal cord.
This was then the entire spinal cord video 1. I invite you to watch the series of spinal cord videos.
