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The skeleton and muscles
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Your skeleton and muscles work together to hold you up, protect you and let you move.
Jobs of the skeleton
An adult skeleton has 206 bones. It has four main jobs:
Support: holds the body up and gives it shape.
Protection: the skull protects the brain; the ribs protect the heart and lungs.
Movement: muscles pull on bones.
Making blood cells: in the bone marrow inside some bones.
Support: holds the body up and gives it shape.
Protection: the skull protects the brain; the ribs protect the heart and lungs.
Movement: muscles pull on bones.
Making blood cells: in the bone marrow inside some bones.
Joints
Bones meet at joints. Hinge joints (elbow, knee) move one way, like a door. Ball-and-socket joints (hip, shoulder) move in many directions.
Cartilage covers the ends of bones so they do not rub. Ligaments join bone to bone. Tendons join muscle to bone.
Cartilage covers the ends of bones so they do not rub. Ligaments join bone to bone. Tendons join muscle to bone.
Muscles work in pairs
A muscle can only pull (by contracting). It cannot push.
So muscles work in antagonistic pairs: when one contracts, the other relaxes.
To bend your arm, the biceps contracts and the triceps relaxes. To straighten it, the triceps contracts and the biceps relaxes.
Muscles exert forces on bones. We can measure the force of a muscle, for example by pulling on a newton meter.
So muscles work in antagonistic pairs: when one contracts, the other relaxes.
To bend your arm, the biceps contracts and the triceps relaxes. To straighten it, the triceps contracts and the biceps relaxes.
Muscles exert forces on bones. We can measure the force of a muscle, for example by pulling on a newton meter.
Explain how the arm straightens at the elbow.
- Muscles can only pull.
- The triceps, at the back of the upper arm, contracts and pulls the forearm.
- At the same time the biceps relaxes.
Answer: The triceps contracts and the biceps relaxes, so the arm straightens.
The skeleton supports, protects, allows movement and makes blood cells. Ligaments join bone to bone; tendons join muscle to bone. Muscles only pull, so they work in antagonistic pairs like the biceps and triceps.
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