Question: Describe the unique characteristics of C1 and C2 as compared to the typical cervical vertebrae. Why is the anatomy of C1 and C2 different than the rest of the cervical vertebrae?

Expert answer

The atlas (C1) and the axis (C2) are the two vertebrae that make up the cervical spine. They are unique in comparison to the other cervical vertebrae, as they play an important role in protecting the brainstem and supporting the head. The atlas is a small, round vertebra that sits on top of the axis. It has no body or spinous process, and it does not articulate with any other bones. Instead, it has two large bony plates (the lateral masses) that extend out from its sides. These serve as attachment points for muscles and ligaments. The most notable feature of the atlas is its large central opening, which allows the spinal cord to pass through. The axis is the second vertebra of the cervical spine. It is slightly larger than the atlas and has a solid cylindrical body. The most notable feature of the axis is its prominent spinous process, which protrudes from the back of the vertebra. This provides attachment points for muscles and ligaments. The axis also has a bony knob (the odontoid process) that projects up from its body. This fits into a notch on the underside of the atlas and allows the head to rotate on the axis. Together, the atlas and axis form a joint called the atlantoaxial joint. This joint allows the head to move in all directions, allowing us to look up, down, side-to-side, and to rotate our head. The unique anatomy of the atlas and axis is essential for these movements.