The C1 and C2 vertebra and the occipital bone of the skull form the atlanto-occipital joint. This type of joint is a synovial joint and allows flexion and extension. This allows the head to make nodding and rotation movements.
The first vertebra of the spine is the C1 vertebra, which is known as the atlas vertebra. The name comes from Greek mythology, because the vertebra supports the globe of the head. The second vertebra is the C2 and is known as the axis, a name that is derived from its role in allowing the head to rotate. The following vertebra continue as C3 through C7.