Antagonistic muscles

KS 3 Science

How do muscles work?

Muscles can only pull.

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.

Muscles are attached to bones by tendons.

The muscles of the upper arm:

Triceps muscle

Biceps muscle

Antagonistic muscle action in the human arm:

Press a muscle to make it contract

Biceps contracts

Triceps relaxes

Raising the arm

Triceps contracts

Biceps relaxes

Lowering the arm

More antagonistic muscles – the leg:

AB

C

D

What happens if:

Muscle A contracts?

Muscle B contracts?

Muscle C contracts?

Muscle D contracts?

- Leg bends at knee.

- Ankle straightens, pointing toes.

- Leg straightens at knee.

- Ankle bends.

Synovial joint structure

Ligament

Ligament

Synovial membrane

Femur (thigh bone)

Synovial fluid

Cartilage