Year 1 · Support and movement · Section 4.4

Muscles

The muscular system

Skeletal muscles attach to bones and help your body move and stay upright. Together they form the muscular system.

Tendons

Tendons attach muscles to bones. The point where a tendon attaches to a bone is an attachment site. Tendons do not actively contract.

When a muscle contracts, it becomes shorter and thicker and pulls on a bone. This can move bones relative to one another. For example, the calf muscles pull on the heel bone through the Achilles tendon.

Antagonistic pairs

Muscles can pull but cannot actively push. Opposing movements are therefore produced by muscles working in antagonistic pairs, such as a flexor and an extensor.

The biceps and triceps are an example. When the biceps contracts, it pulls on the radius and bends the elbow. When the triceps contracts, it pulls on the ulna and straightens the elbow.

Voluntary and involuntary muscle activity

Not all muscles are under conscious control. You can use skeletal muscles voluntarily, for example when walking or lifting, although they also help maintain posture automatically.

Muscle activity in organs such as the stomach, intestines and heart happens involuntarily. Small muscles attached to hairs in the skin also work without conscious control.