Atlas (C1)

Atlas

The atlas is a ring-shaped vertebra unique in lacking a vertebral body and spinous process. It consists of anterior and posterior arches connected by lateral masses. The superior articular facets are concave and cradle the occipital condyles of the skull.

種類 Bone
器官系 Skeletal
身体部位 Spine
ラテン語名 Atlas
FMA ID 12519

機能

The first cervical vertebra that supports the skull. Allows nodding movements (flexion and extension) of the head at the atlanto-occipital joint.

臨床的意義

Jefferson fractures (burst fractures of the atlas) result from axial loading. Atlanto-occipital dislocation is usually fatal. Congenital anomalies include atlas assimilation (occipitalization).

よくある質問

What makes the atlas vertebra unique?
The atlas (C1) is unique among vertebrae because it has no vertebral body and no spinous process. Instead, it consists of an anterior arch, a posterior arch, and two lateral masses. The superior surfaces of the lateral masses bear concave facets that articulate with the occipital condyles of the skull, forming the atlanto-occipital joint responsible for nodding movements of the head.
What movements does the atlas allow?
The atlas facilitates two key movements. The atlanto-occipital joint (between C1 and the skull base) primarily allows flexion and extension — the 'yes' nodding movement. The atlantoaxial joint (between C1 and C2) is a pivot joint that allows approximately 50% of total cervical rotation — the 'no' shaking movement. Together, these joints provide most of the neck's range of motion.
How can the atlas be fractured?
The most common atlas fracture is a Jefferson fracture, a burst fracture caused by axial loading (vertical compression), typically from a diving accident or a blow to the top of the head. The force causes the occipital condyles to drive down onto the lateral masses of C1, splitting the ring at its weakest points. Jefferson fractures may be stable or unstable depending on whether the transverse ligament is intact.

関連構造

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Educational Disclaimer

This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for medical decisions.

Data sources: Terminologia Anatomica, Foundational Model of Anatomy, Wikidata.