Final answer:
Normal movement of adult cranial bones is minimal due to the fused nature of cranial sutures, serving mainly to protect the brain rather than facilitate movement. In infants, suture fusion allows some movement to accommodate brain growth. Skull movement, such as rotation from side to side, is permitted by the atlanto-axial joint.
Step-by-step explanation:
The normal movement of cranial bones in adults is minimal and usually not perceptible under normal conditions. In fact, the cranial sutures in an adult skull are generally fused, which restricts movement between the bones. However, in infants and young children, the cranial sutures are not fully fused, allowing for some movement which facilitates the growth and expansion of the brain. While most bones of the body are connected to allow specific types of movement, the primary purpose of cranial bones is to protect the brain and provide an attachment site for muscles rather than to enable movement.
Concerning skull movements in the broader spectrum of movement types, the articulations formed between the skull, the atlas (C1 vertebra), and the axis (C2 vertebra) allow considerable flexion and extension of the head, such as nodding yes, and lateral flexion, but restrict rotational movement due to the orientation of the articular processes. Rotation of the skull is allowed at the atlanto-axial joint, providing the movement of the head from side to side as in shaking the head 'no'. An abnormal condition that affects cranial bone movement is craniosynostosis, where a premature fusion of sutures prevents normal cranial adjustment to brain growth, resulting in a misshapen skull.