Muscles and Bones

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The Skeleton

Our skeleton is made of more than 200 bones. Calcium and other minerals make the bone strong but slightly flexible. Bone is a living tissue with a blood supply. It is constantly being dissolved and laid down, and it can repair itself if a bone is broken. Exercise and a balanced diet are important for a healthy skeleton.

The skeleton has four main functions:

  • to support the body

  • to protect some of the vital organs of the body

  • to help the body move.

  • blood production


The skeleton supports the body. For example, without a backbone we would not be able to stay upright.


Here are some examples of what the skeleton protects:

  • the skull protects the brain

  • the ribcage protects the heart and lungs

  • the backbone protects the spinal cord.


Some bones in the skeleton are joined rigidly together and cannot move against each other. Bones in the skull are joined like this. Other bones are joined to each other by flexible joints. Muscles are needed to move bones attached by joints.

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Basic structure

If two bones just moved against each other, they would eventually wear away. This can happen in people who have a disease called arthritis. To stop this happening, the ends of the bones in a joint are covered with a tough, smooth substance called cartilage. This is kept slippery by synovial fluid. Tough ligaments join the two bones in the joint and stop it falling apart.

The diagram shows the main features of a joint.


Different types of joint allow different types of movement.

  • Hinge joints allow simple movement, the same as a door opening and closing. Knee and elbow joints are hinge joints.

  • Ball and socket joints allow movement in more directions. Hip and shoulder joints are ball and socket joints.

The bones cannot move on their own - they need muscles for this to happen.

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Antagonisitic Muscles

Antagonistic muscles

Muscles work by getting shorter. We say that they contract, and the process is called contraction.

Muscles are attached to bones by strong tendons. When a muscle contracts, it pulls on the bone, and the bone can move if it is part of a joint.

Muscles can only pull and cannot push. This would be a problem if a joint was controlled by just one muscle. As soon as the muscle had contracted and pulled on a bone, that would be it, with no way to move the bone back again. The problem is solved by having muscles in pairs, called antagonistic muscles.

Biceps and triceps

The elbow joint lets our forearm move up or down. It is controlled by two muscles, the biceps on the front of the upper arm, and the triceps on the back of the upper arm. The biceps and the triceps are antagonistic muscles.

  • when the biceps muscle contracts, the forearm moves up

  • when the triceps muscle contracts, the forearm moves down.

This solves the problem. To lift the forearm, the biceps contracts and the triceps relaxes. To lower the forearm again, the triceps contracts and the biceps relaxes.

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Bone Growth

Bone growth

The bones of embryos are made largely of cartilage. They are soft. The process of ossification uses calcium to create bone as the child grows and matures. Bones gradually become hard and strong. With age bones lose their density and strength. When severe this is called osteoporosis. Eating foods containing calcium and exercising regularly helps bones to develop and stay stronger for longer.

bone in the embryo, young person and adult (

Bone growth

There are 4 types of bone:


Type of boneExampleFunction in sport Long Femur, humerus Movement - to generate strength and speed Short Carpals, tarsal Shock absorption - spreading load Flat (Plate) Ribs, cranium Protection of vital organs, attachment of muscles to help movement Irregular Vertebrae, face Provide shape, protection

The composition of a long bone

bone with epiphysis and diaphysis labelled (

  • Hyaline cartilage - covers the ends of the bones, stops them rubbing together and absorbs shock.
  • Epiphysis - the ‘head’ of the bone.
  • Cancellous bone - spongy bone that stores the red bone marrow; where blood cells are made.
  • Epiphyseal plate – the area where bones grow in length.
  • Diaphysis - the shaft.
  • Compact bone – hard, dense bone. It gives strength to the hollow part of the bone.
  • Periosteum – a protective layer where there is no hyaline cartilage. Ligaments and tendons attach to the periosteum.
  • Medullary cavity/marrow cavity - contains the yellow bone marrow; where white blood cells are made.
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