Final answer:
The atlas (C1 vertebra) is responsible for holding up the head and articulating with the occipital condyles of the skull, forming the atlanto-occipital joint which allows head movement like nodding.
Step-by-step explanation:
The vertebrae that holds up the head and articulates with the occipital condyles of the skull is the atlas (C1 vertebra). The atlanto-occipital joint is the articulation between the superior articular processes of the atlas and the occipital condyles on the base of the skull.
This joint allows for considerable movement including flexion, extension, and lateral flexion of the head, such as nodding in agreement.