KS 3 Science Antagonistic muscles

How do muscles work?

Muscles can only pull.

Muscles are attached to bones by tendons.

Muscles pull when they contract.

Muscles get shorter and fatter when they contract.

Muscles usually work as pairs pulling in opposite directions – these are called antagonistic muscles.

The muscles of the upper arm:

Biceps muscle Triceps muscle

Antagonistic muscle action in the human arm:

Press a muscle to make it contract

Raising the arm

Biceps contracts Triceps relaxes

Lowering the arm

Triceps contracts Biceps relaxes

More antagonistic muscles – the leg: C A D B What happens if:

Muscle A contracts?

- Leg bends at knee.

Muscle B contracts?

- Leg straightens at knee.

Muscle C contracts?

- Ankle straightens, pointing toes.

Muscle D contracts?

- Ankle bends.

Synovial joint structure

Ligament Ligament Synovial membrane Cartilage Synovial fluid Femur (thigh bone)