Atlas (C1 Vertebra): Anatomy, Functions, & Labeled Diagram

Contents

What is the Atlas Bone
Where is the Atlas Bone Located
Quick Information
Functionality
Anatomy
Frontal Arch
Dorsal Arch
Lateral Mass
Transverse Process
References

What is the Atlas Bone

The human vertebral or spinal column can be categorized into the cervical, thoracic, and lumbar spines. The cervical vertebrae encompass the initial 7 vertebrae following the skull down the upper back. The atlas is the first of these 7 cervical vertebrae and is also known as the first cervical vertebrae or C1.

Its name originates from the Greek God Atlas, renowned in mythologies for being sentenced to bear the burden of the Earth on his shoulders for eternity. In a similar manner, the atlas bears the weight of the skull or the globe-like cranium.

Where is the Atlas Bone Located

As mentioned earlier, the atlas is the primary vertebral bone positioned between the skull base and the axis (C2), the second cervical vertebrae.

Quick Information

Nature	Irregular, atypical vertebra
Total Count	1
Connects with	Axis (C1), occipital condyle

Functionality

Being the foremost bone of the vertebral column, the atlas acts as the point of connection between the skull and the spine. Besides upholding the weight of the skull, the petite bone also regulates the head’s range of motion. The atlas forms various articulations and serves as the attachment point for numerous muscles and ligaments crucial to all head movements.

Anatomy

The atlas is a slender ring-shaped bone that does not resemble the typical vertebrae, hence being categorized as an atypical vertebra. It is the most delicate among all the 7 cervical vertebrae and lacks a vertebral body and spinous process. Instead, it comprises an anterior and posterior arch and a lateral mass.

Frontal Arch

It is the bony band that forms the frontal part of the atlas’s ring. There is a bony prominence or tubercle at the front of the bone, known as the anterior tubercle, where the anterior longitudinal ligament attaches.

The smooth circular facet on its rear surface articulates with the dens or odontoid process of the axis, forming the median atlantoaxial joint. It is a pivot joint that allows the rotational movements of the head, such as when you shake your head to say ‘no.’

The anterior atlanto-occipital membrane attaches to its upper border. In contrast, the lower border is the attachment point for the anterior atlantoaxial membrane.

Dorsal Arch

On both sides of the tubercle, on the superior surface of the posterior arch, are two marked depressions or grooves (grooves for the vertebral artery) to allow passage to the C1 spinal nerve and the vertebral artery.

The upper border of the posterior arch provides attachment to the atlanto-occipital membrane, while the lower border is where the posterior atlantoaxial membrane and the first pair of ligamentum flavum attach.

Lateral Mass

There is a smooth, kidney-shaped depression or facet on the upper surface (superior articular facet) of each lateral mass where the bone articulates with the condyles of the skull bone occipital to form the atlanto-occipital joint. This joint allows you to move your head to extend and flex the neck.

There is a short cylindrical projection on the lower surface of the mass called the inferior articular facet. These are incredibly smooth, articulating with the axis bone or C2 to form the lateral atlantoaxial joint. Along with the medial atlantoaxial joint, it also helps with the rotational movements of the head.

The medial surface of the lateral mass has another tubercle, the transverse ligament tubercle, which is the point of attachment for the transverse ligament.