The vertebra named for the Titan who held up the heavens, because it supports the skull
Atlas — C1, supporting the skull on top of the vertebral column.
Anatomy · Bones
Atlas (C1)
First cervical vertebra
Spine · cervical
The atlas is the first cervical vertebra, the topmost bone of the spine, which supports the skull. Unlike all other vertebrae it has no body and no spinous process: it is a ring made of an anterior arch, a posterior arch and two lateral masses. It nods the head at the joint with the occipital bone and turns it at the joint with the axis.
How to spot them
- ▸A ring of bone with no vertebral body and no spinous process, the topmost vertebra
- ▸Two large lateral masses joined by a short anterior arch and a longer posterior arch
- ▸The upper facets are cup-shaped to receive the occipital condyles; the lower facets meet the second vertebra
- ▸The anterior arch has a small facet for the dens of the axis, held in place by the transverse ligament
What to know
The only vertebra with neither a body nor a spinous process, a bony ring instead
Atlas — anterior and posterior arches joined by lateral masses.
The joint between its cup-shaped upper facets and the two condyles of the skull permits nodding, as in saying 'yes'
Atlas — the atlanto-occipital joint.
A burst fracture of this ring, named after a British neurosurgeon, follows a vertical blow to the head such as a dive into shallow water
Atlas — Jefferson fracture, from axial compression.
A transverse ligament stretching between its lateral masses holds the dens of the vertebra below against its anterior arch
Atlas — the transverse ligament of the atlas.
A groove on its posterior arch carries the vertebral artery and the first spinal nerve
Atlas — the groove for the vertebral artery and C1 spinal nerve.
In the embryo its body is donated to the vertebra beneath it, where it becomes that vertebra's tooth-like peg
Atlas — its body becomes the dens (odontoid process) of the axis, which is why it has none.
Key ideas
- Together atlas and axis are the two specialised upper cervical vertebrae: the atlas carries the skull, the axis gives it a pivot to turn on.
- Developmentally, the body of the atlas becomes the dens (odontoid process) of the axis.
Quick-fire facts
- •In Greek mythology Atlas was the Titan who held the heavens on his shoulders
- •The vertebral foramen of the atlas is large, so Jefferson fractures rarely damage the cord at that level
- •Each lateral mass has a superior articular facet for the occipital condyle and an inferior facet for the axis
- •The anterior arch carries a facet for the dens of the axis
- •The atlanto-occipital joints are condyloid synovial joints and permit nodding
- •The medial atlanto-axial joint is a pivot joint; the lateral atlanto-axial joints are plane joints
- •Jefferson fracture is named after the neurosurgeon Geoffrey Jefferson, who described it in 1920
- •It has transverse processes with transverse foramina, like the other cervical vertebrae
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Sources
- TeachMeAnatomy — The Cervical Spine
- OpenStax — Anatomy and Physiology 2e, 7.3 The Vertebral Column
- Kenhub — Anatomical structure of the atlas