Final answer:
The atlanto-occipital joint, a condyloid synovial joint between the occipital condyles of the skull and the atlas (C1 vertebra), facilitates nodding movement of the head.
Step-by-step explanation:
The atlanto-occipital joint is classified as a type of synovial joint, specifically a condyloid joint. This articulation occurs between the occipital condyles of the skull and the superior articular processes of the atlas (C1 vertebra). It permits the skull to rock forward and backward, providing the motion necessary for nodding the head in a "yes" gesture.
The atlanto-occipital joint is distinguished by its U-shaped curvature which is oriented along the anterior-posterior axis. One crucial aspect that separates it from other vertebral articulations is that this joint allows considerable extension and flexion, alongside lateral flexion, but restricts rotation due to the orientation of its articular processes.