Which vertebra is also known as the axis?

Which vertebra is also known as the axis?

• A. C2
• B. C1
• C. C3
• D. C4

Answer: (A)

The idea being tested is identifying the vertebra that serves as the pivot for head rotation. This vertebra is the second cervical vertebra, known as the axis, because it bears the dens (odontoid process) that projects upward to fit with the atlas (the first cervical vertebra). The dens acts as a pivot so the atlas and skull can rotate side to side, which is why this vertebra is called the axis. The atlas sits on top and supports the skull, but it is the dens of the axis that provides the rotational mechanism. The other cervical vertebrae lack this peg-like structure, which is why they don’t function as the axis.

The idea being tested is identifying the vertebra that serves as the pivot for head rotation. This vertebra is the second cervical vertebra, known as the axis, because it bears the dens (odontoid process) that projects upward to fit with the atlas (the first cervical vertebra). The dens acts as a pivot so the atlas and skull can rotate side to side, which is why this vertebra is called the axis. The atlas sits on top and supports the skull, but it is the dens of the axis that provides the rotational mechanism. The other cervical vertebrae lack this peg-like structure, which is why they don’t function as the axis.