What is the Difference Between Atlas and Axis Vertebrae

The main difference between atlas and axis vertebrae is that atlas is the first cervical vertebra, which supports the skull whereas axis is the second cervical vertebra, which forms the pivot upon the atlas. Furthermore, atlas help to hold the head upright while axis allows the head to turn side to side.

Atlas and axis vertebrae are two distinct elements of the vertebral column. They occur at the beginning of the spine, involving in the formation of the neck.

Key Areas Covered

1. What is Atlas Vertebra
     – Definition, Structure, Importance
2. What is Axis Vertebra
     – Definition, Structure, Importance
3. What are the Similarities Between Atlas and Axis Vertebrae
     – Outline of Common Features
4. What is the Difference Between Atlas and Axis Vertebrae
     – Comparison of Key Differences

Key Terms

Atlanto-Axial Joint, Atlas, Axis, Cervical Vertebrae, Neck, Odontoid Process

What is Atlas Vertebra

Atlas (C1) vertebra is the first cervical vertebra of the spine, named from the mythical Greek god who carried the world on his shoulders. That means; the main function of the atlas is to support the globe of the head. Here, it articulates with the occipital bone, which is a flat bone at the back portion of the head. Moreover, the superior articular facets of the atlas are concave and elongate, receiving the condyles of the occipital bone. Also, articulating with the second cervical vertebra, the axis, it allows the head to achieve a wide range of motions. For this, the atlas vertebra contains an oval articulation for the dens of the axis.

Figure 1: Atlas

However, the atlas bone has a distinctive structure in comparison to the other vertebrae in the spine. It is a ring-like vertebra, which does not contain a vertebral body. Also, the main components of the atlas vertebra are the anterior and posterior arches and tubercles, vertebral notches, facets, and transverse processes.

What is Axis Vertebra

Axis (C2) vertebra is the second cervical vertebra of the spine. The main feature of the axis vertebra is the presence of an odontoid process or dens to articulate with the atlas. And, this articulation forms a pivot between the atlas and the axis. Thus, this joint is called the atlanta-axial joint, and its main function is to allow the head to rotate around the neck.

Figure 2: Axis

Also, same as the atlas, axis does not contain a vertebral body. Significantly, the absence of the vertebral body also supports the wide range of motions achievable by the head.

Similarities Between Atlas and Axis Vertebrae

• Atlas and axis vertebrae are the first two cervical vertebrae of the spine.
• They hold the skull, allowing the motion of the head.
• Also, both types of vertebrae occur at the beginning of the neck.
• Moreover, they lack a typical vertebral body.
• Furthermore, they are involved in the formation of the atlanto-axial joint, which forms the pivot, rotating the head.

Difference Between Atlas and Axis Vertebrae

Definition

Atlas refers to the topmost vertebra of the backbone, articulating with the occipital bone of the skull while axis refers to the second cervical vertebra, which serves as a pivot for turning the head. Thus, this is the main difference between atlas and axis vertebrae.

Position

Furthermore, atlas is the first cervical vertebra while the axis is the second cervical vertebra.

Spinous Process

The spinous process is another difference between atlas and axis vertebrae. Atlas lacks a spinous process while axis consists of a large, very strong, and deeply channelled spinous process.

Superior and Inferior Articular Disks

Also, one other difference between atlas and axis vertebrae is that while atlas lacks both superior and inferior articular disks, axis consists of both superior and inferior articular disks.

Odontoid Process

Moreover, atlas contains a section for articulation with the odontoid process while axis contains an odontoid process, which articulates with the atlas. This is another difference between atlas and axis vertebrae.

Importance

Furthermore, another difference between atlas and axis vertebrae is that atlas holds the head upright while axis allows the head to turn side by side.

Conclusion

Atlas is the first cervical vertebra which articulates with the skull. The second cervical vertebra is the axis which articulates with the atlas through the odontoid process. More importantly, the atlas vertebra holds the head upright while axis vertebra allows the rotation of the head by forming a pivot called the atlanto-axial joint in between the atlas and the axis vertebrae. Therefore, the main difference between atlas and axis vertebrae is their position and function.

References:

1. “Atlas Bone Anatomy.” GetBodySmart, 14 Dec. 2017, Available Here
2. “Axis Bone Anatomy.” GetBodySmart, 7 Dec. 2017, Available Here

Image Courtesy:

1. “Atlas vertebrae” By Anatomist90 – Own work (CC BY-SA 3.0) via Commons Wikimedia  
2. “Axis vertebrae” By Anatomist90 – Own work (CC BY-SA 3.0) via Commons Wikimedia