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Core
Diagram - Regions of the vertebral column
Creative commons source by Laboratoires Servier [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The anterior part of the vertebrae is the vertebral body. Vertebral bodies increase in size going down the spine, because the lower vertebrae support more weight. Most adjacent vertebrae are separated by intervertebral discs. There is no disc between the first two vertebrae in the neck (C1 and C2).
The posterior part of a vertebra is formed by the vertebral arch. This arch forms the rear of the vertebral foramen (the hole in the middle of each vertebra). The foramina line up to form the vertebral canal which contains the spinal cord and cauda equina. There are also several bony landmarks to allow for attachment of ligaments and muscles.
Diagram - Labelled structure of lumbar vertebrae
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
Ligaments of the Vertebral Column
Ligaments around the vertebral body:
- The anterior longitudinal ligament runs along the anterior aspect of the vertebral bodies and limits hyperextension (bending too far backwards) of the vertebral column.
- The posterior longitudinal ligament runs along the posterior aspect of vertebral bodies and limits hyperflexion (bending too far forwards) of the vertebral column.
Ligaments around the vertebral arch:
- Ligamentum flavum is located between the laminae (the flat plates of bone that form most of the back of the vertebral arch) of adjacent vertebrae. It is highly elastic and helps the spine straighten again after flexion (bending forwards).
- Interspinous ligaments are located between spinous processes (the bony points you can feel down the middle of the back). They help to limit excessive flexion of the spine.
- Supraspinous ligament runs along the tips of the spinous processes. It also helps to limit excessive flexion of the spine.
- Intertransverse ligaments are located between transverse processes (the bony projections that stick out to each side). They help to limit lateral flexion (bending to the side) and rotation of the spine.
Diagram - The ligaments of the vertebral column
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
Joints of the Vertebral Column
The joints between vertebral bodies are cartilaginous joints (joints where the bones are joined by cartilage); the vertebral bodies articulate (form a joint) with each other indirectly via intervertebral discs. These joints let the vertebral column bear weight.
The intervertebral discs have two distinct regions:
- Annulus fibrosus is the tough outer ring of layered collagen fibres. It surrounds the nucleus pulposus (the soft centre of the disc, described next) and has great tensile strength (it resists stretching forces).
- Nucleus pulposus is the inner, softer, jelly-like region. It resists compression, so the disc as a whole acts as a shock absorber.
Articular facets (the smooth surfaces on the bony projections called articular processes) meet the facets of the vertebra above or below to form facet joints (also called zygapophyseal joints). These are synovial plane joints (joints with a fluid-filled cavity, whose flat surfaces glide over each other). They guide and limit movement. There is one on each side between each pair of adjacent vertebrae.
Diagram - The structure of intervertebral discs
Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The cervical spine (c-spine) is positioned in the neck, and is the most superior part of the spine. It is made up of 7 vertebrae (C1-C7). The c-spine is a very mobile region of the spine, with movements including flexion, extension, rotation and lateral flexion. The two most superior vertebrae, atlas and axis, have some unique features which distinguish them from the other vertebrae.
The cervical nerve roots (the first part of each spinal nerve, where it leaves the spinal cord) exit above their respective vertebrae. For example, the C1 nerve root is above the C1 vertebra. This pattern continues down to C7. There are 8 cervical nerve roots but only 7 cervical vertebrae, so the C8 nerve root exits between C7 and T1. Below this point the nerve roots exit below their respective vertebrae.
- Small vertebral bodies
- The vertebrae do not support much weight, so they are smaller than the vertebrae lower down the spine.
- Bifid spinous processes (the tip is split into two points)
- In typical cervical vertebrae (C3-C6), the spinous process is commonly bifid, although this varies between individuals, especially at C6. C1 has no spinous process; C2 is atypical and commonly has a bifid process. C7 usually has a long, non-bifid spinous process.
- Transverse foramina (openings through the transverse processes)
- Transmit the vertebral arteries (except, usually, in the C7 vertebra).
- The facet joints articulate at an angle of approximately 45 degrees.
Diagram - Cervical Vertebra Structure
Public Domain Source Original from Gray's Anatomy, Derivative by Mikael Häggström, M.D, edited by Dr. Emily Smith [Public domain]
This is the first cervical vertebra. It articulates with the occiput (the occipital bone at the base of the skull) superiorly at the atlanto-occipital joint. This joint permits the characteristic nodding flexion and extension of the head. Lower cervical joints also contribute to flexion and extension of the neck. The atlas also articulates with the axis inferiorly at the atlantoaxial joint (the joint between C1 and C2). This joint is responsible for about half of the rotation in the neck.
It has several features which make it different from the other vertebrae:
- No vertebral body (the body of the atlas fused with the axis during development). Instead, the atlas is a ring of bone made of an anterior arch and a posterior arch joined by two lateral masses.
- No spinous process (only a tiny bump at the back of the ring), so nothing gets in the way when the head nods.
Diagram - The structure of the Atlas vertebra
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
Axis is the second cervical vertebra, and is also atypical compared to the others. One of its features is the odontoid process (or dens), a peg-like projection that rises from the top of the axis and allows the axis to articulate with the atlas (C1). The transverse ligament holds the dens against the front of the atlas. This stops the atlas from being displaced (moving out of position).
Diagram - The structure of the Axis vertebra
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
The 7th cervical vertebra is also atypical. It usually has a single spinous process which is exceptionally long for the cervical spine and is palpable (can be felt through the skin) at the base of the neck. This long spinous process gives the vertebra its name, vertebra prominens (the prominent vertebra). Although C7 has a pair of transverse foramina, the vertebral artery does not usually pass through them.
The thoracic spine is made up of 12 vertebrae (T1-T12), and, along with the sternum and ribs, provides protection to internal organs such as the heart and lungs. It is a relatively immobile region of the spine. The attached ribs and the long, downward-slanting spinous processes substantially limit flexion and extension. The region still rotates, most in the middle vertebrae (T5 to T8), but the rib cage stiffens the spine in every direction, including rotation.
- T1 has a whole facet (a complete surface for a rib head) above and a demi-facet (half a facet) below. T2-T9 usually have a demi-facet above and another below, so a rib head sits across the demi-facets of two neighbouring vertebrae. T10-T12 have one whole facet each.
- Articulation with the head of the ribs.
- T1-T10 have costal facets (surfaces where a rib joins the vertebra) on the transverse processes.
- Articulation with the tubercle (a small bump on the back of a typical rib).
- Spinous processes are long and slant inferiorly.
- The facet joints articulate at an angle of approximately 60 degrees to the horizontal.
Diagram - Superior view of thoracic vertebrae, with key features labelled
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
Diagram - Lateral view of thoracic vertebrae, with key features labelled
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
The lumbar spine is located within the lower back, and is made up of 5 vertebrae (L1-L5). In adults, the spinal cord typically terminates at around the L1 to L2 level and the cauda equina continues from this point. The cauda equina is a bundle of lumbar, sacral and coccygeal nerve roots.
- Large, kidney-shaped vertebral bodies.
- L5 is the largest vertebra as it needs to support the weight of the upper body.
- Triangular vertebral foramen.
- Mammillary processes (small bony bumps) on the superior articular processes for attachment of muscles within the back.
- Accessory processes (small extra bony projections) on transverse processes for attachment of muscles within the back.
- The facet joints are oriented almost vertically (about 90 degrees to the horizontal). This favours flexion and extension and restricts rotation.
Diagram - Labelled structure of lumbar vertebrae
Public Domain Source Anatomy of the Human Body, by Henry Gray, edited by Dr. Emily Smith [Public domain]
The sacrum and coccyx are located at the bottom of the vertebral column.
The sacrum is formed from five fused vertebrae (S1-S5) to create a triangular shape. The sacral nerve roots of the cauda equina pass through the sacral canal within the sacrum.
The coccyx (or tailbone) is usually formed from four vertebrae (three to five in different people) which fuse to form one bone of a triangular shape. It articulates with the sacrum at the sacrococcygeal symphysis (the cartilage joint between the sacrum and the coccyx). This joint allows limited, passive flexion and extension during labour and defaecation (opening the bowels).
Diagram - Structure of the sacrum and coccyx, with key features labelled
Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Edited by: Dr. Ben Appleby
Reviewed by: Dr. Thomas Burnell and Dr. Marcus Judge
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