Year 1 · Support and movement · Section 4.3
How bones are connected
Connections without movement
Some connections between bones allow no movement:
- Fusion: Bones have grown together, as happens between the vertebrae forming the sacrum and within the coccyx.
- Suture: A tight connection between skull bones, with little or no movement in an adult.
Connections that allow movement
Other connections allow movement. Cartilage permits limited movement, for example between ribs and the sternum. Movable joints allow greater movement, including where ribs connect to vertebrae.
Together, these connections allow the rib cage to expand and become smaller during breathing.
The structure of a movable joint
A typical movable joint has several parts:
- Joint head: The rounded end of one bone; in a ball-and-socket joint it fits into a socket.
- Joint socket: A hollow surface in the other bone that receives the joint head.
- Articular cartilage: A smooth layer on the bone ends that reduces friction and wear.
- Joint capsule: A strong covering holding the joint together. Its inner lining produces synovial fluid.
- Ligaments: Strong bands that reinforce the joint and help keep the bones in place, as in the hip.
Three types of joint
Three types studied here allow different movements:
- Ball-and-socket joint: Allows movement in several directions and rotation, as in the shoulder and hip.
- Pivot joint: Allows one bone to rotate relative to another, as where the radius turns around the ulna in the forearm.
- Hinge joint: Mainly allows bending and straightening, as in fingers and the elbow. The knee is commonly described as a modified hinge joint.
Glossary
- Joint
- A connection between bones; movable joints allow bones to move relative to one another.
- Joint capsule
- The strong covering surrounding a movable joint, with an inner lining that produces synovial fluid.
- Joint head
- The rounded end of a bone forming part of a joint.
- Joint socket
- The hollow surface receiving a rounded joint head.
- Synovial fluid
- A slippery fluid that lubricates a joint and helps its surfaces move smoothly.
- Ligaments
- Strong bands of connective tissue that help stabilise a joint.
- Ball-and-socket joint
- A joint allowing movement in several directions, such as the shoulder.
- Suture
- A tight connection between skull bones, allowing little or no movement in adults.
- Pivot joint
- A joint allowing rotation, such as between the radius and ulna.
- Hinge joint
- A joint mainly allowing bending and straightening, such as the elbow.
- Fused bones
- Bones joined together so that they cannot move relative to one another.