Joints
Physical Education: AQA GCSE, topic 1.1.6
Structure of Synovial Joints
Synovial joints are the most common joint in the body. Because they allow movement to happen, they are usually located where 2 bones meet. Synovial joints have the following features:
Cartilage
- Smooth cartilage (tissue) is a protective layer that covers the end of each bone to stop them from rubbing together.
Joint capsule
- The joint is surrounded by a joint capsule that is very tough and fibrous.
- The joint capsule is lined with a synovial membrane. This produces an oily substance called synovial fluid.
- Synovial fluid keeps joints well lubricated (greased to prevent friction) to stop them wearing down and rubbing together.
Ligaments
- The 2 bones in a joint are joined together by ligaments. The ligaments provide strength and keep the bones in place.
- Ligaments help to stop the joint from moving too much and help to stop dislocations (bones moving out of their normal position).
Bursae
- Synovial joints are also protected by bursae. Bursae are small bags of synovial fluid (oily substance) that help to reduce friction in a joint.
- Bursae act like an airbag in a car. They cushion the joint from any external impacts, stopping the bones from coming together.
Hinge Joints
Hinge joints are an important type of freely movable joint. Hinge joints have a limited range of movement, involving flexion (bending) and extension (straightening). Examples of hinge joints include:
Elbow
- The hinge joint in the elbow is made up of the humerus (bone in the upper arm), radius and ulna (bones in the forearm).
- Lets a person bend (flexion) or straighten (extension) their elbow.
- This can be used when taking a shot in basketball.
Knee
- The hinge joint in the knee is made up of the femur (thigh bone), tibia (shin bone) and fibula (calf bone).
- Lets a person bend (flexion) or straighten (extension) their knee.
- This is used when kicking a football.
Ankle
- The hinge joint here is made up of the tibia (shin bone), fibula (calf bone) and talus (ankle bone). This joint allows for different types of movement:
- Plantar flexion: when a person points their toes (e.g. ballet dancers).
- Dorsiflexion: when a person raises their toes upwards.
Test yourself on Joints
Which of the following is not a feature of synovial joints?
What types of movement are allowed by the hinge joint in the ankle?
What type of movement are hinge joints not capable of?