The axis (second neck bone)
Axis (C2) · axis
The second vertebra, with a peg that the atlas pivots around when you shake your head "no".
What it does
The axis has a tooth-like peg, called the dens, that points upward through the ring of the atlas. The atlas and skull swivel around this peg, which is how you turn your head from side to side. About half of all neck rotation happens here.
Surprising fact
The peg of the axis started out in evolution as the body of the atlas, which has fused onto the vertebra below it.
Why it matters
Shaking your head "no" uses this pivot. Because the peg sits right next to the spinal cord, a fracture here is one of the most dangerous neck injuries.
Nearby
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Sources
Drafted with AI help; awaiting a human fact-check against these sources.
Open in the 3D atlas · Suggest a correction · Not medical advice.
3D models: Z-Anatomy & BodyParts3D (CC BY-SA 4.0 / 2.1 JP). Card text CC BY 4.0.