The vertebral column is part of the axial skeleton, and it is made of 33 individual bones during youth, which anatomists classify as irregular bones. Approximately nine of the bones at the terminal end of the spine later fuse in adulthood to form two larger bones: the sacrum and the coccyx.
After the bones of the sacrum and coccyx fuse, the typical vertebral column consists of 26 bones, which anatomists divide into 5 main regions. You’ll want to remember these regions for exams.
5 Main Regions of the Vertebral Column
- 7 cervical vertebrae make up the neck, and they are abbreviated C1-C7. Anatomists also call this region the cervical spine. Seven and cervical both start with the same “s” sound, so that can help you remember that there are seven cervical vertebrae.
- 12 thoracic vertebrae are next, which are abbreviated as T1-T12. It’s easy to remember that there are 12 thoracic vertebrae, because they articulate with the 12 pairs of ribs to form part of the thoracic cage, and twelve and thoracic both start with the letter “t.”
- 5 lumbar vertebrae are inferior (below) the thoracic vertebrae, abbreviated as L1-L5. These vertebrae are larger and denser than the preceding vertebrae, allowing them to support the weight of the upper body. When you add 5 lumbar vertebrae to the 7 cervical vertebrae, you get 12, which is the number of the thoracic vertebrae. Also, people who work 9-5 jobs often complain of having lower back pain when they clock out at 5:00.
- 1 sacrum, which consists of fused sacral vertebrae S1-S5. This triangular bone articulates with the hip bones (os coxae) laterally and the coccyx bone inferiorly to form the bony pelvis.
- 1 coccyx, which consists of 3-5 fused coccygeal vertebrae (Co1-Co4) – This bone is also called the tailbone, and it represents the terminal end of the vertebral column. It articulates with the sacrum bone above.
Intervertebral Discs Anatomy
Twenty-three intervertebral discs separate, anchor, and cushion each vertebra. However, there is no intervertebral disc between C1 (atlas) and C2 (axis), or between the sacrum and coccyx bones.
As you move down the spine, these shock-absorbing pads of fibrocartilage progressively thicken in size, and they consist of two main parts: the nucleus pulposus and the annulus fibrosus.
- The nucleus pulposus is the gel-like center of the intervertebral disc, and it is comprised of a mixture of water, collagen, and proteoglycans. Let the name help you out: Nucleus means the central part of something, and pulposus is a fancy word that means pulp. So this part is the pulpy center of the intervertebral disc.
- The annulus fibrosus surrounds the nucleus pulposus in a series of ringed fibrocartilage layers, which is what the word annulus means (ring). Fibrosus refers to the fibrous nature of the rings, which consist of type 1 and 2 collagen. Each ring layer has fibers arranged at an oblique angle, which alternates to the opposite angle for each subsequent ring, creating an X-like crisscross pattern.
The intervertebral discs are capped superiorly and inferiorly with a thin cartilaginous endplate.
Vertebral Column Curves
When viewed from the side, the vertebral column features four curvatures: two are called primary curvatures, and two are called secondary curvatures.
- Primary curvatures, also called kyphotic curves, are curves that were present during fetal development. These curves are convex, curving outwardly toward the backside. They include the thoracic curvature (T1-T12), and the sacrococcygeal curvature, which includes the sacrum and coccyx bone.
- Secondary curvatures, also called lordotic curves, are curves that slowly begin form postpartum (after the baby’s birth). These curves are concave, curving inwardly toward the front of the body. They include the cervical curvature (C1-C7), as well as the lumbar curvature (L1-L5).
Free Quiz and More Anatomy Videos
Take a free vertebral column anatomy quiz to test your knowledge, or review our vertebral column anatomy video. In addition, you might want to watch our anatomy and physiology lectures on YouTube, or check our anatomy and physiology notes.