Grades 3–5 · Organisms
What helps the ends of bones move smoothly at a joint?
When an elbow bends, the bones move at a joint rather than bending like rubber. At many moving joints, their ends have a smooth covering called cartilage. This tissue separates the hard bone surfaces.
In the diagramCartilage and fluid support smooth joint motionbonecartilagelubricating fluidsupporting ligamentEnlarged moving joint; other joints have different forms.
Cartilage helps spread forces where the bones meet and reduces rubbing during movement. The joint also contains a small amount of slippery synovial fluid. A lining inside the surrounding capsule produces this lubricating fluid.
Tough bands called ligaments help connect bone to bone and guide movement. Muscles pull through tendons to move the joint. Covering, fluid and supporting tissues therefore have different jobs within the same moving structure.
Smooth movement depends on the whole arrangement, not on a hollow gap alone. Different joints allow different motions. An elbow mainly bends and straightens, while a hip’s rounded structure allows movement in more directions.
About this explanation
Starting knowledge: Recognize bones and know that a joint is a place where bones meet.
Sources
- National Institute of Arthritis and Musculoskeletal and Skin Diseases — Health Lesson: Learning About Joints