Joints

The bones in a joint are protected from damage by friction in two ways:

• The ends of each bone are covered by cartilage.
• The space between them is filled with synovial fluid which acts as a lubricant. 

Muscles are attached to bones by tendons and made of white fibrous tissue. Muscles can only move a bone when they contract and so always work in antagonistic pairs.

• BALL AND SOCKET - allows radial movement in any direction, e.g. shoulder
• SADDLE - back and forth, up and down but no rotation, e.g. finger
• PIVOT - allows rotation around an axis, e.g. neck
• HINGE - extension and retraction of an appendage, e.g. knee
• FIXED - restricted movement, e.g. pelvis
• GLIDING - bones slide past each other, e.g. ankle