🦴 1. How Do We Move? — The Role of Bones and Joints
Our body can bend, stretch, run, swim, and do many complex movements. But how? The answer lies in our
bones, muscles, and joints working together!
Key terms:
- Skeleton — The entire framework of bones in the body. It gives the
body its shape and supports it.
- Bone — Hard, rigid structure that forms the skeleton. Cannot bend on
its own.
- Joint — The place where two bones meet. Joints allow movement.
- Muscle — Soft tissue attached to bones. When muscles contract
(shorten), they pull on bones to cause movement.
- Cartilage — A slightly flexible tissue found at joints, the tip of the
nose, and outer ear. Softer than bone.
- Ligament — Strong, elastic tissue that connects bone to bone at a
joint.
- Tendon — Strong, non-elastic cord that connects muscle to bone.
🔗 2. Types of Joints
Different joints in our body allow different types of movements. Let's study each type:
| Type of Joint |
Movement Allowed |
Location in Body |
Example analogy |
| Ball and Socket Joint |
Movement in ALL directions (360°) — up, down, sideways, circular |
Shoulder (humerus + shoulder blade), Hip (femur + pelvis) |
Like a ball inside a cup — ball can rotate in any direction |
| Hinge Joint |
Movement in only ONE direction (like a door hinge) — opens and closes |
Knee, Elbow, Fingers (knuckles), Ankle |
Like a door hinge — can only swing one way |
| Pivot Joint |
Rotation around one axis (twisting movement) |
Neck (between skull and first vertebra — atlas and axis) |
Like a key turning in a lock |
| Fixed/Immovable Joint |
No movement at all — bones fused together |
Skull (cranium bones fused together), Pelvis |
Like two puzzle pieces glued together |
| Gliding Joint |
Limited sliding movement in many directions |
Wrist, Ankle (between small bones) |
Like book pages sliding over each other |
📸 Image Prompt
An educational diagram showing different types of joints in a human body outline:
(1) Ball and socket joint highlighted at the shoulder and hip — shown as a ball sitting in a cup shape,
(2) Hinge joint highlighted at the knee and elbow — shown as a door hinge symbol, (3) Pivot joint at the
neck — shown as a cylinder rotating around a rod, (4) Fixed joint in the skull — shown as interlocking
zigzag lines. Each joint type labeled with name and location. Clean anatomical educational illustration
on white background, simple clear style for Class 6.
Fig. 8.1 — Types of joints in the human body
💪 3. Muscles — The Movers
Bones cannot move on their own — they need muscles to pull them. Muscles are made of special
cells that can contract (shorten) and relax (lengthen).
How muscles cause movement (using the arm as example):
- The biceps (front of upper arm) and triceps (back of upper arm)
work as a pair called antagonistic muscles.
- To raise the forearm: Biceps contracts (shortens) + Triceps relaxes (stretches) →
arm bends up
- To lower the forearm: Triceps contracts + Biceps relaxes → arm straightens down
When one muscle of a pair contracts, the other must relax. They never both contract at the same
time!
📸 Image Prompt
A side-by-side diagram of a human arm showing muscle action: Left image — arm bent
upward (bicep curl): Biceps muscle shown as a thick bulging muscle on the front of upper arm (labeled
"Biceps: Contracted/Shortened"), Triceps shown as thin on the back (labeled "Triceps:
Relaxed/Stretched"). Right image — arm straight down: Biceps shown as thin (labeled "Relaxed"), Triceps
shown as thick (labeled "Contracted"). Both images show the humerus, radius and ulna bones. Clean
educational anatomy style, labeled arrows showing contraction direction.
Fig. 8.2 — Antagonistic muscle action: Biceps and Triceps
🐍 4. How Different Animals Move
Not all living things move the same way. Different animals have special structures for movement:
| Animal |
How It Moves |
Special Feature |
| Earthworm |
By extending and contracting its body using longitudinal and circular muscles. The
small bristles (setae) grip the ground. |
No skeleton — uses hydrostatic pressure (fluid inside body) |
| Snail |
Glides on a single muscular "foot" (uses mucus to slide smoothly) |
Produces slimy mucus for frictionless gliding |
| Cockroach |
Has 3 pairs of legs (6 legs), 2 pairs of wings; can walk and fly |
Exoskeleton (hard outer covering); segmented body |
| Fish |
Swim using fins; body moves in S-shaped curves (tail fin gives propulsion) |
Streamlined body shape; fins for steering and balance |
| Bird |
Flies using wings (modified forelimbs), walks using legs |
Hollow bones (light weight); powerful breast muscles for wing flapping |
| Snake |
Large number of vertebrae + many ribs; body curves sideways — slithering/serpentine
motion |
Very flexible spine; scales grip the ground |
Most birds have hollow bones. This makes their skeleton very light without sacrificing
strength — essential for flight. A bird's bones weigh less than its feathers! Compare this to fish which
have solid bones.
📸 Image Prompt
A 3x2 grid educational illustration showing 6 animals and how they move: (1)
Earthworm — microscopic view of setae bristles gripping soil, body shown in S-shape, (2) Snail — sliding
on one muscular foot on a leaf, (3) Cockroach — 6 legs and wings labeled, (4) Fish — swimming in water
with fins labeled (dorsal, tail/caudal, pectoral), body in slight S-curve, (5) Bird in flight — wings
spread showing hollow bone cross-section inset, (6) Snake — slithering in S-shaped curve with vertebrae
backbone visible. Labels for each animal's type of movement. Clean educational illustration, white
background.
Fig. 8.3 — Different animals and their types of movement
🦴 5. The Human Skeleton
The skeleton is the complete framework of 206 bones in the
adult human body. It is divided into two main parts:
1. Axial Skeleton: The central core of the skeleton
- Skull — 8 bones fused to form a protective case for the brain
- Vertebral column (backbone/spine) — 33 vertebrae stacked like building blocks,
forming the central support; protects the spinal cord
- Rib cage (thoracic cage) — 12 pairs of ribs + sternum (breastbone); forms a cage to
protect heart and lungs
2. Appendicular Skeleton: The limbs and their girdles
- Pectoral girdle (shoulder bones) + Arms (humerus, radius, ulna)
- Pelvic girdle (hip bones) + Legs (femur, tibia, fibula)
- Hands (8 carpal, 5 metacarpal, 14 phalanges per hand)
- Feet (7 tarsal, 5 metatarsal, 14 phalanges per foot)
Important Bones to Remember:
| Bone Name |
Location |
Function |
| Skull (Cranium) |
Head |
Protects the brain |
| Vertebral column |
Back (central) |
Supports body; protects spinal cord |
| Ribs |
Chest (12 pairs) |
Protects heart and lungs |
| Femur (thigh bone) |
Upper leg |
Largest/strongest bone in body |
| Humerus |
Upper arm |
Connects shoulder to elbow |
| Sternum |
Centre of chest |
Where ribs attach; protects heart |
| Patella |
Knee |
Kneecap; protects knee joint |
📝 6. Quick Revision
- Skeleton = 206 bones; gives shape, supports, and protects organs
- Bone connects to bone via Ligament; Muscle connects to bone via
Tendon
- Ball and socket (shoulder, hip) — all-direction movement
- Hinge joint (knee, elbow) — one-direction movement
- Pivot joint (neck) — rotational movement
- Fixed joint (skull) — no movement
- Muscles work in pairs: Biceps + Triceps; when one contracts, the other relaxes
- Earthworm — setae + muscle contraction; Fish — fins + streamlined
body
- Birds — hollow bones for light weight; powerful breast muscles for flying
- Rib cage protects heart and lungs; Skull protects brain;
Vertebral column protects spinal cord
