Inclusive Anatomy
Structure:
Vertebra C1, also known as the atlas, is the first and superior-most cervical vertebra.[1] It is a ring-shaped vertebra that differs from typical vertebrae in that it lacks both a vertebral body and a spinous process.[1] Instead, vertebra C1 consists of paired lateral masses connected by anterior and posterior arches, forming a complete ring.[1]
Each lateral mass bears a kidney-shaped superior articular surface that articulates with the occipital condyles of the skull, allowing support of the cranium.[1] Inferiorly, the lateral masses articulate with vertebra C2 (axis).[1] The transverse processes extend laterally from the lateral masses and contain the foramina transversaria, which transmits the vertebral artery and vein.[1]
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The anterior and posterior arches connect the lateral masses and each possesses a tubercle on its external surface.[1] On the posterior surface of the anterior arch is a facet for articulation with the dens of the axis, stabilized by the transverse ligament of the atlas.[1] The transverse processes of vertebra C1 are positioned more laterally than those of inferior cervical vertebrae, contributing to the overall width of the atlas.[1]
Function:
The primary function of vertebra C1 is to support the weight of the skull and facilitate head movement.[1] The lateral masses act functionally as a vertebral body by bearing the load of the cranium.[1]
Vertebra C1 plays a critical role in stabilizing the atlanto-occipital joint, allowing flexion and extension of the head (the “yes” motion).[1] The widened transverse processes increase the leverage for muscle attachment, enhancing control of head and neck movements.[1] Additionally, the foramina transversaria allow passage of the vertebral arteries, veins, and sympathetic nerve fibers as they ascend toward the cranial cavity.[1]
References:
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Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 6th ed. International ed. Lippincott Williams & Wilkins; 2010.
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Jackowe DJ, Biener MG. Atlas and talus. J Anat. 2022;240(6):1174-1178. doi:10.1111/joa.13613
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Singer C. The strange histories of some anatomical terms. Med Hist. 1959;3(1):1-7. doi: 10.1017/s0025727300024200
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