6.3 2.2.4 joints

Joints

http://www.bbc.co.uk/science/humanbody/body/factfiles/joints/ball_and_socket_joi nt.shtml

A joint is formed when two or more bones come into contact

Types of joints

Joints are divided into 3 groups according to their degree of movement.

1. Immovable joints such as the bones of the skull (known as sutures) which are fused.
2. Partly movable joints have cartilage between them which allows for a small degree of movement e.g. between the vertebrae also called cartilaginous joints .
3. Synovial joints are freely movable and are divided into 4 groups

• Hinge joints - e.g elbow and knee joints which allow movement in one plane only
• Ball and Sock et joints - e.g. shoulder and hip joints allows free movement in almost all directions.
• Pivot joint - between atlas and axis vertebrae – allows for turning movement of head
• Gliding joints - between ankle bones and wrist bones – allows for rotational movements of hands and feet

Structure of synovial joint

• The joint is completely enclosed in a bag-like joint capsule forming a synovial cavity.
• The joint capsule is lined by a synovial membrane which secretes synovial fluid filling the entire cavity thereby reducing friction
• The ends of the bones are covered in hya l ine articular cartilage
• In addition to the joint capsule, other ligaments are present which attach bones to each other

SYNOVIAL JOINT