Body Movements
Body Movements
What you'll learn
- The skeletal system: bones and their functions.
- Types of joints and their movements.
- How muscles work with bones to produce movement.
- Movement in other animals.
Key concepts
Skeletal system
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The skeleton is the framework of bones that supports the body.
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Functions of the skeleton:
- Gives shape and support to the body.
- Protects delicate internal organs (skull protects brain; ribcage protects heart and lungs).
- Provides attachment for muscles.
- Blood cells are produced in bone marrow.
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An adult human body has 206 bones.
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Bones are connected to each other at joints.
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Cartilage: flexible, smooth connective tissue at the ends of bones — cushions and reduces friction.
Major bones:
| Bone | Location | What it protects/does |
|---|---|---|
| Skull | Head | Protects brain |
| Vertebral column (spine) | Back (33 vertebrae) | Supports body; protects spinal cord |
| Ribcage (12 pairs of ribs + sternum) | Chest | Protects heart and lungs; helps in breathing |
| Femur (thigh bone) | Upper leg | Longest and strongest bone |
| Patella | Knee | Protects knee joint |
| Humerus | Upper arm | — |
Types of joints
Joint: place where two or more bones meet.
| Joint type | Movement | Examples |
|---|---|---|
| Ball and socket joint | Movement in all directions (360°) | Shoulder, hip |
| Hinge joint | Movement in one direction only (like a door hinge) | Knee, elbow, fingers |
| Pivot joint | Rotational movement only | Neck (atlas-axis vertebrae) — allows head to rotate |
| Fixed (immovable) joint | No movement | Skull bones (cranium) |
| Gliding joint | Slight sliding movement | Wrist and ankle bones |
Muscles
- Muscles produce the force needed for movement by contracting (getting shorter).
- Muscles are attached to bones by tendons (strong, flexible connective tissue).
- Ligaments connect bone to bone at joints.
How muscles work:
- Muscles can only pull — they cannot push.
- To move a bone in one direction, one muscle contracts and the opposing muscle relaxes.
- Muscles work in pairs (antagonistic pairs):
- Bicep contracts → arm bends (flexion) → tricep relaxes.
- Tricep contracts → arm straightens (extension) → bicep relaxes.
Types of muscles:
| Type | Control | Location | Example |
|---|---|---|---|
| Voluntary (skeletal) | Conscious control | Attached to bones | Bicep, quadricep |
| Involuntary (smooth) | Automatic | Walls of internal organs | Stomach, intestine, blood vessels |
| Cardiac | Automatic | Heart only | Heart muscle |
Movement in animals
| Animal | Structure used for movement | Special feature |
|---|---|---|
| Earthworm | Muscular contractions + tiny bristles (setae) | Extends and contracts segments |
| Snail | Muscular foot | Secretes mucus to reduce friction |
| Fish | Fins + flexible body with bones | Tail fin propels; other fins steer/balance |
| Bird | Wings (modified forelimbs) + hollow bones | Hollow bones reduce weight |
| Snake | Scales + muscular body — no limbs | Scales grip surface; waves body |
Quick check
- How many bones does an adult human body have?
- Name the four types of movable joints. Give an example of each.
- Where is a ball and socket joint found? Why is this joint type there?
- Why must muscles work in antagonistic pairs? Give an example.
- How does an earthworm move?
Open the Practice tab for graded questions on Body Movements.
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