Spine Basics: How Many Vertebrae, Structure, Functions, and Terminology Explained with 3D Anatomy

Introduction

In this article, we cover the basics of the spine (vertebral column), the foundation of human anatomy.

The spine supports the head, moves the trunk, and protects the spinal cord, all at the same time. Many muscles, ligaments, and nerves attach to or emerge from it, so a solid grasp of the spine makes every other region much easier to learn.

We hope this article, together with the app, helps deepen your understanding.

Let's look at the basics of the spine and how to study it in human anatomy.

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What is the spine (vertebral column)?

The spine, or vertebral column, is a column of individual bones called vertebrae stacked one on top of another. It runs down the center of the trunk from the base of the skull to the pelvis.

The words "spine", "backbone", and "vertebral column" all refer to the same structure. A single bone is a vertebra; the plural is vertebrae.

How many vertebrae are there?

From top to bottom, the vertebrae are grouped into five regions.

In children the sacral and coccygeal vertebrae are still separate, giving 32 to 34 vertebrae in total. In adults they fuse into the sacrum and the coccyx, so the spine is usually counted as 26 bones: 7 cervical + 12 thoracic + 5 lumbar + 1 sacrum + 1 coccyx.

A common way to remember the movable vertebrae is the sequence 7-12-5, like a day: breakfast at 7, lunch at 12, dinner at 5.

Basic structure of a vertebra

Vertebrae differ in size and shape from region to region, but they share the same basic plan.

At the front is the vertebral body, a cylindrical block that bears the weight of the body. Behind it is the vertebral arch, and the opening enclosed by the body and the arch is the vertebral foramen. When the vertebrae are stacked, these openings line up to form the vertebral canal (spinal canal), the tunnel through which the spinal cord passes.

Several projections extend from the arch. The spinous process points backward and can be felt as the bumps along the midline of the back. The transverse processes project to the left and right. The superior and inferior articular processes of neighboring vertebrae interlock to form small facet joints (zygapophysial joints).

Each region has its own features. The first cervical vertebra, the atlas, is a ring that carries the skull. The second, the axis, has a peg-like projection (the dens) that acts as the pivot for turning the head. Thoracic vertebrae have facets that articulate with the ribs, and lumbar vertebrae have the largest bodies because they carry the most weight.

Intervertebral discs and ligaments

Between adjacent vertebral bodies sits an intervertebral disc, a pad of cartilage made of a gel-like center (the nucleus pulposus) surrounded by rings of fibrous tissue (the annulus fibrosus). The discs absorb shock and allow the spine to bend.

The spine is also reinforced by ligaments along its front and back: the anterior longitudinal ligament on the front of the vertebral bodies, the posterior longitudinal ligament on their back, the ligamenta flava connecting the arches, and the interspinous and supraspinous ligaments connecting the spinous processes. In the neck the supraspinous ligament broadens into the nuchal ligament.

For more detail, see our articles on the intervertebral disc, the supraspinous ligament, and the nuchal ligament.

The natural curves of the spine (the S-curve)

Seen from the side, the spine is not straight but forms a gentle S. The cervical spine curves forward (lordosis), the thoracic spine curves backward (kyphosis), the lumbar spine curves forward again, and the sacrum curves backward.

The thoracic and sacral curves are present from before birth and are called primary curves. The cervical and lumbar curves develop as an infant learns to hold up its head and then to stand and walk, so they are called secondary curves. Together these curves act like a spring, cushioning the impact of walking and jumping and balancing the head and trunk with minimal effort.

Functions of the spine

Support

The spine carries the weight of the head and trunk and transmits it through the pelvis to the legs. Because the load increases toward the bottom, the vertebral bodies grow progressively larger from the cervical to the lumbar region.

Movement

Each facet joint allows only a small amount of motion, but added together across the whole column they produce large movements: flexion (bending forward), extension (bending backward), lateral flexion (bending sideways), and rotation (twisting). The regions differ in what they do best: the neck rotates freely, the thoracic spine moves little because of the ribs, and the lumbar spine is built mainly for flexion and extension.

The spine is moved and held upright by the back muscles, including the erector spinae and the multifidus.

Protection

The vertebral canal houses the spinal cord, which continues down from the brain. Spinal nerves branch off to the left and right and leave the canal through the intervertebral foramina, the openings formed between adjacent vertebrae, on their way to the rest of the body. The spine surrounds this pathway with bone and protects it. See also our article on the spinal nerves.

Terminology in English and clinical shorthand

The spine is also called the vertebral column or, informally, the backbone. One bone is a vertebra, and the plural is vertebrae. The regions are the cervical, thoracic, lumbar, sacral, and coccygeal vertebrae; the fused bones are the sacrum and the coccyx.

Clinicians number the vertebrae with a letter and a number: C1 to C7 for the cervical spine, T1 to T12 for the thoracic spine, L1 to L5 for the lumbar spine, and S1 to S5 for the sacral segments. A level between two vertebrae is written with a slash, so L4/L5 means the level between the fourth and fifth lumbar vertebrae.

How to study the spine in human anatomy

Here is a concrete way to study the spine using a 3D anatomy app.

Start with the whole column, then one vertebra

Display the entire spine in 3D, view it from the side to see the S-curve, and trace the boundaries between the cervical, thoracic, and lumbar regions. Then isolate a single vertebra and rotate it to check the body, arch, spinous process, transverse processes, and articular processes. Comparing one vertebra from each region makes the regional differences obvious.

Use cross-sections and the nervous system view

A cross-section shows how the vertebral foramina line up to form the spinal canal and how thick the discs are between the bodies. Turning on the nervous system shows the spinal cord inside the canal and the spinal nerves leaving through the intervertebral foramina, so you can see for yourself how the spine protects the nerves.

Make full use of the memo function

Write down anything you notice while studying so you don't forget it. The memo function supports text, saved images, and handwritten notes, so you can choose whichever fits. Jotting down the 7-12-5 count and the C/T/L/S shorthand, then tagging the memos, makes them easy to review later.

Test yourself regularly with quizzes

Make up your own questions, such as "How many cervical vertebrae are there?", "What is the other name of the second cervical vertebra?", or "What is the tunnel the spinal cord runs through called?", and answer them. Use the app's quiz function to check your understanding at regular intervals.

Summary

In this article we covered the basics of the spine using the app!

The spine consists of 7 cervical, 12 thoracic, and 5 lumbar vertebrae plus the sacrum and coccyx, and it has three jobs: support, movement, and protection. Once you know the basic structure of a vertebra and the S-curve, related topics such as the discs, ligaments, back muscles, and spinal nerves fall into place.

See also our articles on related structures:

Thank you for reading this far.

We hope this article has helped you with your anatomy studies.

Learning is a long journey with no end, but we sincerely wish you success. Let's keep learning together!

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