Question

what is the primary motion occurs at the atlanto-occipital joint (co-c1)
neck rotation
neck flexion and extension
side flexion

Explanation:

The Atlanto - occipital joint (CO - C1) is a condyloid joint formed between the occipital condyles and the superior articular facets of the atlas (C1). This joint primarily allows for neck flexion (bending the head forward) and extension (bending the head backward). Neck rotation is mainly associated with the Atlanto - axial joint (C1 - C2), and side flexion is a more complex movement that involves multiple cervical vertebrae but is not the primary motion at the Atlanto - occipital joint.

Answer:

Neck flexion and extension