An articulation, or joint, is where two bones come together.
In terms of the amount of movement they allow, there are
three types of joints: immovable, slightly movable and freely
movable.
Synarthroses
Synarthroses are immovable joints. The singular form is
synarthrosis. In these joints, the bones come in very close
contact and are separated only by a thin layer of fibrous
connective tissue. The sutures in the skull are examples
of immovable joints
Amphiarthroses
Slightly movable joints are called amphiarthroses. The singular
form is amphiarthrosis. In this type of joint, the bones are
connected by hyaline cartilage or fibrocartilage. The ribs
connected to the sternum by costal cartilages are slightly
movable joints connected by hyaline cartilage. The symphysis
pubis is a slightly movable joint in which there is a fibrocartilage
pad between the two bones. The joints between the vertebrae
and the intervertebral disks are also of this type.
Diarthroses
Most joints in the adult body are diarthroses, or
freely movable joints. The singular form is diarthrosis.
In this type of joint, the ends of the opposing bones
are covered with hyaline cartilage, the articular
cartilage, and they are separated by a space called
the joint cavity. The components of the joints are
enclosed in a dense fibrous joint capsule. The outer
layer of the capsule consists of the ligaments that
hold the bones together. The inner layer is the synovial
membrane that secretes synovial fluid into the joint
cavity for lubrication.
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Because all of these joints have a synovial membrane, they are
sometimes called synovial joints.
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