成人快手

Key points

  • Muscles can only contract and relax, so they always work in pairs called antagonistic muscles.
  • Skeletal muscle is joined to bones. Its cells contract to make bones move and joints bend.
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Video

Can you answer these questions based on the video?

1. What does 鈥榮keletal鈥 mean?

2. In which directions do antagonistic muscles pull?

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The skeleton

There are more than 200 individual bones in the body. These make up the skeleton, which has four main functions:

  • to support the body
  • to protect some of the vital organs of the body
  • to make blood cells
  • to help the body move
a diagram of the skeleton labelled with the names of the bones
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Joints

woman dances wearing pink jeans and striped top
Image caption,
The elbow and knee are just two of the joints you might use when dancing

, like your elbows and knees, are places where bones are able to move in different directions. But bones are unable to move on their own, so muscles pull on them at joints.

Strong, cord-like tissues called attach to the ends of bones either side of joints. Bones are not connected directly to muscles. are also strong cord-like tissues but these attach the bones in the joint to muscles which contract and relax to move them.

woman dances wearing pink jeans and striped top
Image caption,
The elbow and knee are just two of the joints you might use when dancing
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Muscles

Your muscles are made of bundles of muscle cells forming muscle There are three different types of muscle:

  • Cardiac muscle cells contract and relax to pump blood around our bodies.
  • Smooth muscle cells make up thin sheets of muscle, such as the stomach lining.
  • Skeletal muscle is joined to bones. Its cells contract to make bones move and joints bend.

Antagonistic muscles

Muscles can only This means for skeletal muscles, they can only pull on bones. They cannot push them back. This would mean that if your joints were moved by one muscle, then you would be able to move them once and not return them to their original position. We can move our joints backwards and forwards because our skeletal muscles come in pairs, called

Knee

The knee joint has two muscles that move the shin up or down. These are the hamstrings and the quadriceps.

  • To pull the shin backwards (before the ball is kicked), the hamstrings contract and the quadriceps relax.
  • To move the shin forwards (when the ball is kicked), the quadriceps contract and the hamstrings relax.
Image gallerySkip image gallerySlide 1 of 2, knee with contracted hamstrings and relaxed quadriceps, The hamstrings contract and bring the shin back as the quadriceps relax

Elbow

The elbow joint has two muscles that move the forearm up or down. These are the biceps on the front of the upper arm and the triceps on the back of the upper arm.

  • To raise the forearm, the biceps contract and the triceps relax.
  • To lower the forearm, the triceps contract and the biceps relax.
Image gallerySkip image gallerySlide 1 of 2, Elbow with contracted biceps and relaxed triceps, The biceps contract and raise the forearm as the triceps relax
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Test your knowledge

Quiz

Test questions

Write a paragraph to answer the following question. Tap 'Show answer' to see five points you could have included.

Describe the specific muscles that work to move your elbow.

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Atomic Labs game. game

Try out practical experiments in this KS3 science game

Atomic Labs game
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More on Living organisms

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