The vertebral column (spine)
The vertebral column (spine or backbone) is a curved structure composed of bony vertebrae that are interconnected by cartilaginous intervertebral discs. It is part of the axial skeleton and extends from the base of the skull to the tip of the coccyx. The spinal cord runs through its center. The vertebral column is divided into five regions and consists of 33 vertebrae interlaced by strong joints and ligaments.
Although the spine can be a pain in the back, it’s function is very important. Thanks to the spine, you can twist, bend and sway your trunk in almost any direction. Your vertebral column also protects your fragile spinal cord and helps support the weight of the upper body. Therefore, it’s important to take good care of it and maintain a good posture at all times!
|Regions||Cervical, thoracic, lumbar, sacral, coccygeal|
|Typical vertebra||Vertebral body, vertebral arch (pedicles, lamina), vertebral processes (spinous, transverse, articular)|
|Joints||Intervertebral discs, uncovertebral, zygapophysial (facet), craniovertebral (atlanto-occipital, atlanto-axial), costovertebral, sacroiliac|
|Ligaments||Longitudinal (anterior, posterior), ligamenta flava, interspinous, supraspinous, nuchal, alar, cruciate ligament of atlas, costotransverse, ligaments of head of rib (intra-articular, radiate)|
|Curvatures||Cervical lordosis, thoracic kyphosis, lumbar lordosis, sacral kyphosis|
|Movements||Flexion, extension, lateral flexion, lateral extension, rotation|
|Vasculature||Segmental arteries and vertebral venous plexus (internal, external)|
|Nerves||Meningeal branches of spinal nerves|
In this article we’ll explore the anatomy and functions of the vertebral column.
- Joints and ligaments
- Spine curvature and movements
- Nerves and vasculature
- Related videos
- Related diagrams and images
The spine, vertebral column, or backbone is defined as the bony structure that runs from the inferior aspect of the occipital bone of the skull to the tip of the coccyx. However, the spinal cord is the tubular nervous tissue that travels through the vertebral canal of the vertebral column.
How many vertebrae do we have? The vertebral column consists of 33 vertebrae in total, divided as follows:
- Cervical vertebrae (7)
- Thoracic vertebrae (12)
- Lumbar vertebrae (5)
- Sacrum (5 fused)
- Coccyx (3-4 fused)
No two vertebrae are identical. They vary in size and characteristics, especially from one region to the next. However, they all have the following basic structure:
- Vertebral body - the large cylindrical part located anteriorly that gives strength to the spine. They are involved in weight bearing. Their size increases as one descends down the vertebral column. Adjacent vertebral bodies are separated by intervertebral discs.
- Vertebral arch - the structure located posterior to the body. It consists of two pedicles and two laminae. The pedicles contain vertebral notches (superior, inferior) which form intervertebral foramina. These facilitate the passage of spinal nerves from the spinal cord. The pedicles, laminae, and body of each vertebra form a cavity (vertebral foramen). The vertebral canal is the space throughout the spinal column that is enclosed by the vertebral foramina.
- Vertebral processes - there are seven in total all projecting from the vertebral arch: one spinous process (posteroinferior), two transverse processes (posterolateral), and four articular processes. The latter contain articular facets. The vertebral processes serve as attachment points for ligaments and back muscles. They also take part in joint formation.
The seven cervical vertebrae form the cervical spine of the neck. They are located between the skull and the thoracic vertebrae and have the smallest and thinnest intervertebral discs. However, they are the most mobile in the entire vertebral column. In addition, cervical vertebrae have distinctive features like transverse foramina, two tubercles (anterior, posterior) and split (bifid) spinous processes. Here’s an illustration depicting the cervical spine anatomy.
Three cervical vertebrae are atypical. The atlas (C1) consists of two arches (anterior, posterior) and contains two lateral masses. The masses articulate with the occipital condyles of the skull, supporting its weight. The axis (C2) contains an upwards tooth-like projection (dens or odontoid process) and two superior articular facets. These facilitate articulation with the atlas and head rotation. Vertebra prominens (C7) has the longest spinous process. It’s the bony point sticking out the most at the back of your neck. The remaining cervical vertebrae (C3-C6) are typical.
More information and distinctive features of the cervical vertebrae are included in the following resources:
The twelve thoracic vertebrae form the second region of the vertebral column, the thoracic spine (upper back). They play a role in forming the thoracic cage. Thoracic vertebrae contain several distinctive features: costal facets that articulate with the ribs, heart shaped vertebral bodies, smaller vertebral foramina, and long and strong spinous and transverse processes which point inferiorly. The first four (T1-T4) and last four (T9-T12) thoracic vertebrae share some characteristics with the cervical and lumbar spine, respectively. The middle four (T5-T8) are typical thoracic vertebrae. The vertebral bodies contain thicker discs compared to the cervical spine.
Do you want to find out what characteristics set the thoracic vertebrae apart? Master thoracic spine anatomy using the following article, video, and quiz:
The five lumbar vertebrae form the lumbar spine (lower back). They have the largest vertebral bodies in the entire vertebral column, a feature that facilitates weight bearing. The pedicles and laminae are thick and strong. Their spinous processes are short and sturdy for the attachment of strong lumbar muscles. The articular processes are oriented differently compared to other types of vertebrae. The lumbar spine also contains accessory and mammillary processes. L5 is the largest vertebra of the entire human body – it supports and transmits body weight to the base of the sacrum. The spinal cord terminates as the conus medullaris (medullary cone) at the level of the L1/L2 vertebra.
Lumbar spine anatomy is not too difficult to learn due to the typical structure of the vertebrae. Learn more about them below:
The sacrum consists of five sacral vertebrae fused together. It is located between the lumbar spine (lumbosacral angle) and the coccyx and forms part of the pelvis. Its main role is to transmit the entire weight of the upper body to the pelvis in order to reach the lower limbs.
The sacrum has a base, an apex, and three surfaces (pelvic, posterior, lateral). Within its center is the sacral canal which is the continuation of the spinal canal. The sacral canal contains the cauda equina of the spinal cord. Sacral foramina (anterior, posterior) allow for the exit of the spinal nerves. The sacral crests (median, intermediate, lateral) represent the fused processes of the sacral vertebrae.
Do you want to find out more about the sacrum? Take a quick peak below!
Think back to the last time you fell on your gluteus maximus. It’s one of the few times when you become aware of your tailbone simply because it was so incredibly painful. The tailbone (coccyx) articulates with the sacrum and consists of three to four fused coccygeal vertebrae. It has two surfaces (pelvic, posterior), short transverse processes, and coccygeal cornua. The coccyx is a point of attachment for the gluteus maximus and coccygeal muscles. The filum terminale of the spinal cord stops at the level of the first coccygeal vertebra (Co1).
Complete your knowledge of spine anatomy by tackling the following resources about the coccyx and sacrum. Pathologies affecting the vertebral column, such as radiculopathy and spondylolisthesis have also been included.
Joints and ligaments
Joints of the vertebral bodies
After learning about individual vertebrae, it’s time to explore how the vertebral column is kept together as a unit. Adjacent vertebral bodies are joined by symphyses called intervertebral discs. The exceptions are C1-C2 and after S2, where such symphyses do not exist. Intervertebral discs are composed of a fibrous outer ring (annulus fibrosus) that surrounds a gelatinous nucleus (nucleus pulposus). Their role is to serve as shock absorbers, prevent friction and permit a small degree of flexibility between vertebrae. The lumbar spine is the most susceptible to disc herniations due to its location and significant involvement in weight bearing. The vertebral bodies of the cervical vertebrae are also interconnected by uncovertebral joints (clefts of Luschka).
The vertebral bodies and intervertebral discs are reinforced by two fibrous, longitudinal ligaments. The anterior longitudinal ligament extends along the exterior, anterolateral aspect of the vertebral bodies from the base of the skull to the sacrum. Its role is to limit extension and prevent hyperflexion of the spine. The posterior longitudinal ligament runs inside the vertebral canal along the posterior surface of the vertebral bodies, from C2 to the sacrum. Its main function is to prevent posterior herniation of the intervertebral discs.
The anatomy of the intervertebral discs is explored in detail in the following articles:
Joints of the vertebral arches
Adjacent vertebral arches are connected by synovial joints called zygapophysial (facet) joints. They are formed between superior and inferior articular facets. These joints facilitate flexion and extension in the cervical and thoracic spines. They also permit rotational movements in the thoracic spine.
The vertebral arches are strengthened by several accessory ligaments:
- Ligamenta flava - connecting adjacent laminae. They prevent separation of the lamina during sudden flexion of the vertebral column.
- Interspinous ligaments - join spinous process of nearby vertebrae.
- Nuchal ligament - extends from the skull (occipital protruberance) to the spinous processes of C7 where it merges with the supraspinous ligament.
- Supraspinous ligament - a long band that connects the tips of the spinous processes.
There are two craniovertebral (synovial) joints formed between the skull and the atypical vertebrae of the cervical spine: atlanto-occipital and atlanto-axial. The atlanto-occipital joints are formed between the lateral masses of the atlas (C1) and the occipital condyles of the cranium. They permit flexion, extension, and sideways tilting of the head. Thanks to them, you can nod in approval. The atlanto-axial joints (two lateral, one median) are located between the C1 and C2 vertebrae. They facilitate a pivot motion of the head as in during a disapproving shake.
Several membranes and ligaments also connect the atlas, axis, and skull. The atlanto-occipital membrane (anterior, posterior) runs between the edges of the foramen magnum and the atlas, limiting the movement of the atlanto-occipital joints. The alar ligaments and tectorial membrane connect the axis to the occipital bone and floor of the cranial cavity, respectively. They prevent excessive rotation of the atlanto-axial joints. The cranium, atlas and axis are interconnected by the cruciate ligament of the atlas.
If you want to find out how craniovertebral joints and ligaments allow you to nod and shake your head, take a look at the following:
The costovertebral (synovial) joints represent the connection between the thoracic vertebrae and ribs. One type of costovertebral joints (costocorporeal joints) unite the head of ribs with the costal facets of two adjacent vertebral bodies (T2-T9), one superior and one inferior. The costocorporeal joints articulate with the costal facet of a single vertebra at T1, T10 and T11. They permit the ribs to rotate, ascend, and descend during breathing movements. The second type (costotransverse joints) forms between the rib tubercle and the transverse processes of the corresponding vertebra (T1-T10).
The two joints are reinforced by three costotransverse ligaments (medial, lateral, superior). These run from the transverse processes to the neck and tubercle of the ribs, respectively. In addition, intra-articular and radiate ligaments of head of rib also support these joints. These extend to the sides of the vertebral bodies and the interconnecting intervertebral discs.
Last but not least, the sacrum of the vertebral column and the iliac bones are involved in forming the sacroiliac joints. They occur between the corresponding auricular surfaces and tuberosities of these two bones. The sacroiliac bones permit very little mobility, being involved in the transmission of weight from the upper to the lower body.
The stability of the sacroiliac joints is maintained by the sacro-iliac (anterior, interosseous, posterior), sacrotuberous, and sacrospinous ligaments. The latter two also connect to the coccyx in addition to the ilium and sacrum.
Are you curious to better understand all anatomical structures that prevent the vertebral column from disintegrating? Check out the following!
Spine curvature and movements
While contortionists seem like they lack a vertebral column, the remaining humans definitely feel its capabilities and limitations. The spine is capable of six movements: flexion (bending forward), extension (bending backwards), lateral flexion (right/left), lateral extension (returning to normal from lateral flexion), and rotation (twisting). All of these movements are influenced by the previously mentioned joints and ligaments and by thoracic and back muscles. Movements in the cervical and lumbar regions of the spine are freer than the thoracic and sacral ones.
The adult spine has four curvatures:
- Cervical lordosis (posterior concavity)
- Thoracic kyphosis (anterior concavity)
- Lumbar lordosis
- Sacral kyphosis
Kyphoses are primary curvatures while lordoses are secondary curvatures. More details about the movements and curvatures of the spine are provided below:
Nerves and vasculature
The blood supply of the vertebral column is provided by segmental arteries. They are named posterior intercostal, subcostal, lumbar, iliolumbar, and sacral arteries in the thoracic, lumbar, and sacral regions of the spine. All originate from the aorta except those in the cervical region and the iliolumbar artery. Segmental arteries of the cervical region stem from the vertebral and ascending cervical arteries instead and the iliolumbar artery is a branch of the posterior trunk of the internal iliac artery.
Looking for a Kenhub app to learn the vertebral column on the go? You don't need one! Kenhub's website is interactive and fully responsive on all your electronic devices, so simply start using it anywhere to ease your learning.
As the segmental arteries follow the course of the vertebrae, they provide equatorial branches to the vertebral body and posterior arteries to the vertebral arch. At the level of the lamina, spinal branches travel to the intervertebral foramina to enter the vertebral canal and supply its contents via vertebral canal arches (anterior, posterior).
Venous blood from the vertebral column is drained via spinal veins into vertebral venous plexuses (internal, external). Basivertebral veins drain the vertebral bodies into the internal vertebral venous plexus. The two vertebral venous plexuses empty into the intervertebral veins. In turn, these empty into the vertebral and segmental veins of the neck and trunk.
The vertebral column is innervated by the meningeal branches of the spinal nerves. They divide into ascending and descending branches that supply the vertebrae, intervertebral discs, and ligaments.
Check out the following articles and videos that explain the neurovasculature of the vertebral column. After that, tackle the quizzes to cement your knowledge.