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Part II :Movement and Feeding : Index

Movement on Land Homepage
Joints in the Skeleton
Movement on Land Summary (useful for revision)
Movement on Land : Questions

Introduction : Animal Movements
Carnivores, Herbivores and Omnivores
Movement in the Air
Movement in Water
Recognizing and Choosing Food
How Animals Feed : Carnivores
How Animals Feed : Herbivores
How Food is Digested
The Digestive System of Other Animals
Foods which give us Energy

Topic Chapters Index

 

Diagram showing the muscles in a straightened arm © Shirley Burchill

 

 

Diagram showing the muscles in a bent arm © Shirley Burchill

 

HOW MUSCLES WORK

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The Antagonistic Action of Muscles

Muscles usually work in pairs. A good example of a pair of muscles working together can be seen in the human arm. The muscle at the front of the arm is called the biceps muscle. The muscle at the back of the arm is called the triceps muscle. When the biceps muscle is working (contracted) the triceps muscle is relaxed. When the triceps muscle is contracted the biceps muscle is relaxed. This is called antagonistic action of muscles because they are always working in opposite ways.

Contraction of the biceps muscle bends the arm. Contraction of the triceps muscle straightens the arm.

There are muscles in the legs which work the same way to bend the knees, ankles and toes.

The lion and the antelope both have well developed muscles in their limbs. They need to use them often. For both it is a matter of life and death.

Arthropods also have muscles but we cannot see them because they are inside of their hard body-covering. These muscles also work in pairs as vertebrate muscles do.

 

Diagram showing the muscles in a flexed arthropod joint © Shirley Burchill

 

Diagram showing the muscles in an extended arthropod joint © Shirley Burchill

 

If you look at a locust or a grasshopper you can see that their back legs are much thicker than the others. This is because they use them for hopping. The muscles inside the back legs are much larger than the muscles in the other legs.

 

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