Final answer:
The atlantoaxial joint is a pivot-type joint that enables the head to turn side to side. It is formed by three articulations involving the atlas and axis vertebrae and is unique to the cervical region of the vertebral column.
Step-by-step explanation:
The atlantoaxial joint is responsible for allowing rotational movements of the head, such as turning the head from side to side to indicate 'no.' This joint is a pivot-type joint located between the atlas (C1 vertebra) and the axis (C2 vertebra). Specifically, it consists of three articulations: two between the superior articular processes of the axis and the inferior processes of the atlas, and one pivot joint between the dens of the axis and the anterior arch of the atlas.
The dens, or odontoid process, is held in place by a strong ligament, allowing the atlas to rotate on top of the axis. This capacity for rotation is distinct within the vertebral column, as the range of motion available varies by region. The thoracic region permits only rotation, while the lumbar region allows for extension, flexion, and lateral flexion but not rotation. In contrast, the atlanto-occipital joint, formed by the articulations between the occipital condyles of the skull and the atlas, facilitates the nodding motion, or the 'yes' movement.