Depending on the type of joint, such separated elements may or may not move on one another.
This article discusses the joints of the human body particularly their structure but also their ligaments, nerve and blood supply, and nutrition.
In order to describe the main types of joint structures, it is helpful first to summarize the motions made possible by joints.
These motions include spinning, swinging, gliding, rolling, and approximation.
Spin is a movement of a bone around its own long axis, it is denoted by the anatomical term rotation.
An important example of spin is provided by the radius (outer bone of the forearm) this bone can spin upon the lower end of the humerus (upper arm) in all positions of the elbow.
When an individual presses the back of the hand against the mouth, the forearm is pronated, or twisted;
When the palm of the hand is pressed against the mouth, the forearm is supinated, or untwisted.
Swing, or angular movement, brings about a change in the angle between the long axis of the moving bone and some reference line in the fixed bone.
Flexion (bending) and extension (straightening) of the elbow are examples of swing.
A swing (to the right or left) of one bone away from another is called abduction, the reverse, adduction.
Joints are the areas where two or more bones meet. Most joints are mobile, allowing the bones to move.
Joints consist of the following:
Cartilage
A type of tissue that covers the surface of a bone at a joint;
Cartilage helps reduce the friction of movement within a joint;
Synovial membrane
A tissue called the synovial membrane lines the joint and seals it into a joint capsule;
The synovial membrane secretes synovial fluid (a clear, sticky fluid) around the joint to lubricate it;
