Answer:
The human skeleton, and in general the human body, have mechanisms that allow them to move. This movement, especially when it comes to rigid bone structures, comes thanks to something called joints. Joints, are the connection between two bone structures, and while some will allow motion because they are cushioned and movable, others will be static, depending on the function they play. In the human backbone, this is particularly necessary: both motion and protection of motion. How can this be accomplished? Through two types of joints.
In general, demifacet and facet joints are just that, joints, but while one will allow the vertebrae of the backbone to move without damaging itself and the vital spinal cord and the nerves, the others will protect from motion, or limit it.
Demifacet joints, thus, are particular in the sections of the column, T1 through T9. The name comes because it is a joint that is divided into two sections, one on the upper side of the vertebrae, and the other on the lower side, and it provides an articulation point between the vertebrae in the thoracic region of the spine and the ribs. The range of motion in this joint is very limited, only enough for the thoracic cavity to expand and close with breathing.
The Facet joints are the most common type of articulations in the vertebral column and they are full synovial joints between vertebrae that allow these bones to move in different directions, without either damaging the bodies of each bone, and protects the nerves that exit from the spina cord towards the different parts of the body. Facets can be distinguished from their position all along the column, and because they are synovial, which means, they have a cushion between them, for shock absorption.
