The Entire Spine, Explained in 16 Minutes

0:00 Let’s talk about the vertebral column. It’s made up of bones called vertebrae, stacked on top of each other - and even though they look similar, they actually change shape and function depending on where you are in the spine. So the way we’re going to understand the full anatomy of it is by first answering the questions, How and why do we divide the spine into different regions? Why does the spine have curves, and what happens when those curves go wrong? Then we’ll look at the basic structure of a vertebra, which is common across the majority of the vertebra throughout the column. After that we'll talk specifically about the cervical vertebrae, thoracic vertebrae, lumbar vertebrae and the sacrum and coccyx. What’s up everyone, my name is Taim. I’m a medical doctor, and I make animated medical lectures to make different topics in medicine visually easier to understand. If you’d like a PDF version or a quiz of this presentation, you can find it on my website, along with organized video lectures to help with your studies. Alright, let’s get started. Look at this. The vertebral column, spine, backbone. This is the core part of the axial skeleton in vertebrates. It goes from your skull, all the way down to the tailbone. And when you look at it, really just don’t think anatomy right

1:09 now. Look at this. You’ll notice that at the top, it’s much smaller, this is to not limit the head, neck and arm movement, as you go to the middle, the spine starts getting a little bit bigger, curved outwards, this is to hold the ribs and protect your thorax. A bit more down, it gets even bigger, large vertebrae responsible for holding the weight of your body, and allows for a wide range of body motions. A little bit more down, and you’ll notice the bones are now fused, into a shield looking unit that hold a lot of our muscles that help us keep our body upright. Now, because the spine has different functions at different regions, we divide it into parts. We have 7 cervical vertebrae, 12 Thoracic Vertebrae, 5 lumbar vertebrae, 5 fused sacral vertebrae, and 3 to 5 coccygeal vertebrae, averaging to about 4 coccygeal vertebrae in human. This means that in

2:04 humans, our spine is composed of 33 vertebrae. Now let’s analyze the spine a little bit more, this is really important. Why does your spine have curves? For this, let’s put the spine back into this guy. In an upright position, we humans have physiological curvatures. And we divide them into Primary curvatures, and Secondary curvatures. Primary curvatures are present in the fetus, and remain the same in adults. We call this type of curvatures ‘’kyphosis’’, outwards curvatures which is normal to a certain degree, but it can be abnormal if it's exaggerated. These are Thoracic kyphosis and sacral kyphosis The thoracic and sacral curvatures are termed primary curves because they are present in the fetus and remain the same in the adult. As the child grows, lifts the head, and begins to assume an upright position, the secondary curves develop. These are known as lordosis, and you need

3:01 to separate this term because a normal lordosis is a gentle inward curve, and abnormal lordosis, or also called hyperlordosis, is If the curve is too deep, causing lower back pain, muscle imbalances, postural issues and so on. The cervical curve forms when the infant is able to hold up his or her head (at three or four months) and sit upright (at nine months). The lumbar lordosis forms between twelve to eighteen months when the child begins to walk. Any exaggeration of these natural curves causes problems, and is often due to postural problems, muscle atrophy, or weakening of bones. Now. Let’s turn our guy to the front. Turn on the xray machine, and then give him a little injury. If there is a lateral curve of the vertebral column, any wedging and rotation of vertebrae, we call this condition scoliosis. So, that was the curvatures of the spine. Now, let’s go ahead and remove the spine for this guy

4:00 again. The vertebrae across different regions of the spine may differ, but the majority of them share some basic structure. And I wanna remind you again, remember we got cervical vertebrae in the neck, we got vertebrae in the thorax, lumbar vertebrae, sacrum and the coccyx. The majority of vertebrae in the cervical region look like this. In the thoracic region, they look like this. And in the lumbar region, this is what they look like. Pay close attention now. They all have a vertebral body. They all have a vertebral arch, and they all have processes. This is interesting, you see now they do have common basic structures, but notice they do differ slightly from one another depending on the function of that specific vertebra. Let’s look at these three structures a little bit more detailed. Focus on the vertebral body for a moment. Here we can see the intervertebral surface, which connects with the

4:51 intervertebral disc. Surrounding the surface is the anular epiphysis, which is a ring of compact bone on the external margin of the body, containing a secondary ossification centre. Now, let’s move on to the Vertebral arch. The vertebral arch is typically divided into two regions. It’s the posterior part of the vertebral arch called Lamina, and the anterior narrowest part of the vertebral arch, that connect to the vertebral body, called Pedicle. Throughout all vertebrae in the spine, there’ll also be a large hole in the middle called the vertebral foramen, bordered by the body and arch. Now, let’s do the processes. The process are simple, there’s the spinous process that’s pointing backwards, and it’s the one you often can see and feel on a person's back. On the sides we can see the transverse processes which differs in size across the vertebrae, and we can see the

5:45 superior and inferior articular processes. To understand these, let’s look at a sideview of the spine. The Superior articular process is the bony part on the vertebra that faces upward and forms a joint with the vertebra above, whereas the Inferior articular process goes downward and connects with the vertebra below. When those vertebra go together, they form the intervertebral foramen, and the vertebral canal. Why are they significant? Let me show you why. Within the vertebral canal is going to be a lot of different structures, and the noticeable ones are the spinal cord as you see here, along with meninges around them. There are Blood vessels (e.g. anterior and posterior spinal arteries, venous plexuses). There are ligaments like the ligamentum flava, and the posterior longitudinal ligament. The spinal cord is going to give off some spinal nerves, that unite to form the spinal nerve root,

6:41 that exit through the intervertebral foramen. Not of significance for the foramina here, but on this model we can also see the sympathetic chain ganglia. Alright, what else can we see? Between the vertebral bodies of the spine, you’ll find intervertebral disks highlighted here in blue. They allow the vertebral column to be flexible and act as shock absorbers during activities. So, we saw that the vertebrae across the spine share some common basic structures. But there are specific structures that make vertebrae districts based on where they’re located. Most of the 7 cervical vertebrae share specific structures, thoracic vertebra has some specific structures for the ribs, Lumbar vertebrae has some specific structure, and even, the sacrum and coccyx. Now, the cervical vertebral column consists of 7 vertebrae and forms the cervical lordosis. The cervical vertebrae generally share similar

7:35 morphological features across C3-C7. The first cervical vertebrae C1, is called atlas, and it greatly differs from the basic structure of the vertebrae as it does not have a vertebral body. During development, its body fuses with the dens of the second cervical vertebrae, called Atlas. Let’s cover the specific features across those vertebrae. Now, if we look at a superior view of the normal cervical vertebrae, The first noticeable difference from a normal vertebra, is that the transverse process is different. It contain an extra hole here called the vertebral foramen. This exists because the vertebral artery goes through it, that supplies our brain. A little side note here, on the transverse process of the 6th cervical vertebra, there’s an anterior tubercle specifically called the "carotid" tubercle. This one is prominent and palpable in the neck. And clinically, it's important because the common

8:26 carotid artery can be compressed against it to control bleeding or check the pulse. That’s why it’s called the "carotid" tubercle. Alright. Other things here on the transverse process are the anterior tubercles, which are remnant of the cervical ribs. Posterior tubercle, and the Groove for spinal nerve. We can also see the articular processes, superior articular process points dorsocranially, and inferior articular process points ventrocaudally. And the spinous process is distinct here in this region as well in that it’s bifid, with the exception of C1 and C7. It is shaped this way because it increases the surface area for muscle and ligament attachment, especially since neck muscles are involved in fine movements and posture. Now let’s do the C1 Atlas. For this one, let’s start by looking at it from a superior view, as you see here. It’ll make sense in a moment. So,

9:19 what do we see? Remember we said that C1 greatly differs from the basic structure of the vertebrae as it does not have a vertebral body. Instead, it has an anterior and a posterior arch. There’s a lateral mass, which contain the articulating surfaces. And since we’re looking at a superior view, we’re looking at the superior articulating surface, which articulates with the occipital condyle on the occipital bone. Usually at the tip of the posterior end we got a spinous process, right? Here we only got a posterior tubercle, which is the embryological remnant of the spinous process, and acts as the origin of the rectus capitis posterior minor and the attachment of the nuchal ligament. Anteriorly is the anterior tubercle, and on the inside of the arch, is the facet for dens, which articulated with the dens of C2. There is one more structure we can’t really see from this view, and it’s a groove associated with the posterior

10:17 arch. If we go back to looking at th vertebral artery again. This artery actually winds around the posterior parts of the lateral mass, forming the groove for vertebral artery, as it head up to your brain, helping form the circle of willis. Now, let’s look at C2. Just for orientation. Here is the anterior part, here is the posterior part. C2 Axis is distinct in that it has a dens that fits perfectly on the facet of C1. Now this is really interesting, The reason why C2 has Dens, is that this is actually the embryological remnant of the body of atlas, somewhere along the development, the body of C1 separated, and fused with C2 giving an apex. And this resulted in C1 having just an arch on the anterior and posterior sides. This Dens has an anterior articular facet which articulates with the atlas, and a Posterior articular facet, articulating with the transverse ligament of the atlas. So that was the cervical vertebra. Now let’s do the specific

11:19 structures associated with the thoracic vertebra. The thoracic vertebral column consists of 12 vertebrae and form the thoracic kyphosis. Thorax has ribs, right? Because the ribs are connected to the thoracic vertebrae, they restrict the movements of the thoracic vertebral column. Now, we can divide the thoracic vertebra into typical vertebrae, usually 2nd to 9th, and atypical vertebra, which are T1, T10, T11 and T12. The typical vertebra is distinct because it has a superior costal facet, inferior costal facet and a transverse costal facet. The superior and transverse facet both provide a point of attachment for the same rib, while the inferior facet is usually for the rib below. So, this is the typical general usual thoracic vertebrae. Why do we have atypical vertebra? It’s a very subtle difference. But T1 is atypical because it has a single 'full' facet for the head of the first rib,

12:21 and it has an Inferior demi facet for the head of the second rib, and just morphologically, T1 bears some resemblance to low cervical vertebrae. For the other atypical ones. T9 is highly variable, some sources mention it as atypical as well just because it might not have an inferior demifacet. But generally T10-T12 are the main ones. T10 has a singe full facet. While T11 and T12 both have a single full facet while also the facet on the transverse process is rudimentary. So, those are the specific features of the thoracic vertebra. The lumbar vertebral column consists of 5 large vertebrae that share morphological characteristics and form the lumbar lordosis. These vertebrae are huge, have strong body and processes that support the weight of your body. There’s a lot of heavy

13:14 stress on your lower back as you move, so these bones have to be able to support that. The special thing here is that the transverse processes are less well developed on the lumbar vertebrae. They rather have something called costal process, which are the lumbar equivalents of the ribs. So they’re the embryological remnant of the lumbar ribs. Otherwise the body is tall, wide and kidney shaped, and the spinous process is flat and quadrate shaped when viewed from the side. That was the lumbar vertebral column. Now, let’s do the Sacrum and Coccyx. These are interesting. The sacrum is formed by fusion of the 5 sacral vertebrae. The coccyx consists of 3–5 fused rudimentary vertebrae. Very variable. They form the sacral kyphosis. Let’s isolate them and look at an anterior view. Again here we see that there were initially 5 sacral vertebrae that fused. How do we generally divide the sacrum? We have a base at the top, and an apex at the bottom, connecting

14:11 to the coccyx via an intervertebral disk. The base. If you look here. Has a promontory, which is a part of the terminal line of the pelvis. And we got the Superior articular process, which articulated with the corresponding inferior articular process of the 5th lumbar vertebra. From this view we can also see the sacral wings. These are the lateral parts of the sacrum, and contain the auricular surface which is articulates with the ilium. And if we look from the backside, we can see the sacral tuberosity, which serves as the attachment for the posterior sacroiliac ligament. Alright. What else can we see? On the pelvic surface, we can see the anterior sacral foramina, which are 4 pairs of opening that transmit the anterior rami of the sacral spinal nerves. And we can see the transverse ridges, those are lines that formed due to the fusion of vertebrae. Now, let’s look at the sacrum from a posterior view.

15:09 Here we can see the posterior sacral foramina, which are 4 pairs of openings that transmit the posterior branches of the sacral spinal nerves S1–S4. Apart from this we can also see the lateral sacral crest, which is due to the fusion of the transverse processes. Median sacral crest, due to fused spinous processes, and the medial sacral crest, due to fusion of the articular processes. Within the sacrum, there’s a canal called the sacral canal. This is an extension of the vertebral canal, and it goes all the way down to open at the sacral hiatus, transmitting the spinal nerves S5 and coccygeal nerve. This opening is bordered laterally by the sacral horns, which are remnants of the articular processes. Now, Coccyx. This small tailbone is the end of the vertebral column. It’s highly variable between people, but in average there are 4 vertebrae here that fused and made this bone. If we turn

16:06 it around. We can see something called coccygeal cornua, which are horns pointing cranially, and are remnants of the articular processes. So that was all I had for the bones of the vertebral column. The vertebral column don’t work alone, they are connected by a network of ligaments and membranes that stabilize it during movement and help prevent injuries. And interestingly, a lot of back problems start right there, with the ligaments. If you want to understand how those ligaments are arranged and what they do, check out the next video. I’ll see you there. If you want a handmade PDF version of this lecture, take a quiz to test your knowledge, or access an organized list of all my videos, you can find everything on my website. Thanks for watching! See you in the next one.