What type of joint allows turning from side to side?

The correct answer is a pivot joint, which is specifically designed to allow rotational movement. This type of joint permits one bone to rotate around another, facilitating turning motions, such as turning the head from side to side.

For instance, the joint between the first and second cervical vertebrae (the atlas and axis) in the neck functions as a pivot joint, allowing the head to rotate. The unique structure of pivot joints, where the rounded end of one bone fits into a ring formed by another bone or ligament, supports this rotational movement.

Understanding the characteristics of the different types of joints helps to clarify why the pivot joint is the correct choice in this context. Hinge joints primarily allow for flexion and extension and do not facilitate rotation. Ball and socket joints allow for a wide range of movements including rotation, but are not specific to side-to-side turning. Ellipsoid joints, while allowing for two-dimensional movement, do not provide the rotational movement that a pivot joint does.