This article deals with anatomical joints. For information about joints in the context of cannabis, try: Spliff.
A joint in the human body (and other animals) is the area where two bones interact, about which a movement can be formed.
There are many joints in the human body, but they can be divided into different groups.
The ends of each bone are covered in smooth
articular cartilage, they are also lubricated with
synovial fluid, this reduces
friction and enables smooth movements to be produced.
The whole joint is contained in the joint capsule, which consists of a tough outer layer which helps to stabilise the joint, and a synovial membrane which produces synovial fluid.
Most of the joints that provide a lot of movement are synovial joints.
Synovial joints can be further grouped by their shape, which controls the movement they allow:
Such as the
elbow[?] (between the
humerus and the
ulna). These joints act just like the hinge on a door, allowing
flexion and
extension in just one plane.
Such as the
hip joint[?]. These allow a wide arrange of movement.
Such as the
knee. When the knee is
extended there is no rotation, when it is flexed some rotation is possible. A
condyloid joint is where two bones fit together with an odd shape (e.g. an
ellipse), and one bone is concave, the other convex.
Such as the
elbow[?] (between the
radius and the
ulna). This is where one bone rotates about another.
Such as at the
thumb (between the
metacarpal[?] and
carpal). Named so because of their shape,
saddle joints, allow movement in a variety of directions.
Such as in the
carpals of the wrist. These joints allow a wide variety of movement, but not much distance.
Unlike
synovial joints these do not allow much movement. An example of this joint is the
pubic symphysis[?].
These are not designed to allow any movement. The sutures in the
skull are an example.