How are immovable joints defined?

Immovable joints, also known as fibrous joints, are specifically characterized by their lack of movement. These joints are typically found in the adult skull where the bones are fused together, providing stability and protection for the brain. The design of these joints allows them to resist movement, which is essential for safeguarding vital structures, preventing injuries, and maintaining structural integrity. The rigid nature of these joints is crucial, especially in areas where flexibility is not necessary, reinforcing the role of immovable joints in overall skeletal stability.

In contrast, the other options describe types of joints that allow for varying degrees of movement. Junctions allowing movement, such as diarthroses, typically include synovial joints that are intended for mobility. Flexible joints in the spine refer to cartilaginous joints that do permit some movement for flexibility and shock absorption. Lastly, joints allowing rotation, like the neck, belong to a category of movable joints that facilitate specific types of motion, which contrasts with the defining feature of immovable joints.