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The bone is named for Atlas of Greek mythology, just as Atlas bore the weight of the heavens, the first cervical vertebra supports the head. [1] However, the term atlas was first used by the ancient Romans for the seventh cervical vertebra (C7) due to its suitability for supporting burdens. [2]
In anatomy, the axis (from Latin axis, "axle") is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests. The spinal cord passes through the axis. The defining feature of the axis is its strong bony protrusion known as the dens, which rises from the superior aspect of the bone.
The atlanto-axial joint is a joint between the atlas bone and the axis bone, which are the first and second cervical vertebrae.It is a pivot joint that provides 40 to 70% of axial rotation of the head.
The atlas (C1) and axis (C2) are the two topmost vertebrae. The atlas (C1) is the topmost vertebra, and along with the axis forms the joint connecting the skull and spine. It lacks a vertebral body, spinous process, and discs either superior or inferior to it. It is ring-like and consists of an anterior arch, posterior arch, and two lateral masses.
C1 is also called the atlas, and C2 is also called the axis. The structure of these vertebrae is the reason why the neck and head have a large range of motion. The atlanto-occipital joint allows the skull to move up and down, while the atlanto-axial joint allows the upper neck to twist left and right.
The number of those in the cervical region, however, is only rarely changed. [4] The vertebrae of the cervical, thoracic, and lumbar spines are independent bones and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis, on which the head ...
The atlas is a ring around the roughly cone-shaped extension of the axis (second cervical segment). The axis acts as a post around which the atlas can rotate, allowing the neck to swivel. There are 23 discs in the human spine: 6 in the neck region, 12 in the middle back region, and 5 in the lower back region. [3]
It also will miss vertical or posterior displacement of the cervical spine. [5] Other measurements include occiput-atlas distance, angle between anterior arch of atlas and axis, vertical distance between posterior arch of atlas and spinous process of axis, vertical atlanto-dens interval, and joint space between C1 and C2. [6]