Body Movements — Bones, Joints & Skeleton for Class 6

Have you ever tried standing still like a statue for five minutes? It’s really hard! Our body is always moving — even when we think we’re sitting quietly, our heart is beating, our chest is rising and falling, and our eyes are blinking. All of this movement happens because of our skeleton, muscles, and joints working together.

Let’s understand how our body is built for movement.

CBSE Class 6 Chapter 8 asks about types of joints, functions of the skeleton, and how different animals move. These are very commonly tested topics in school exams and Olympiads.

Why Do We Need a Skeleton?

Think of a building. Without a steel frame inside, the walls would collapse. Our skeleton works the same way — it’s the inner frame that holds us up.

The skeleton does three big jobs:

1. Support: Our bones hold our body upright. Without them, we’d be a wobbly pile of skin, like a deflated balloon. The backbone especially helps us stand straight.

2. Protection: Some bones act like armour. The skull protects our brain — the softest and most important organ in our body. The rib cage wraps around our heart and lungs like a bony cage. The spine protects our spinal cord.

3. Movement: Bones work with muscles to help us walk, run, jump, and write. Bones act as levers, and muscles pull on them to create movement.

Our skeleton is also the place where blood cells are made! The soft tissue inside bones called bone marrow produces red blood cells, white blood cells, and platelets.

Bones and Cartilage

Bones

Bones are hard and strong. They are made mainly of calcium and phosphorus, which give them their hardness. An adult human body has 206 bones.

Bones are not completely solid — they have a spongy inner part which keeps them light without making them weak. This is why we can move quickly without feeling super heavy.

Cartilage

Now feel the tip of your nose. Press it gently. Did you notice it bends? That’s because it is made of cartilage, not bone.

Cartilage is softer and more flexible than bone. Touch the top of your ear — that firm but bendable part is also cartilage.

Easy way to remember: Bone = hard, cannot bend. Cartilage = softer, can bend. Check your nose and ear — cartilage. Check your shin — bone.

Cartilage is also found between bones at joints — it acts like a cushion so bones don’t grind against each other. Without cartilage, our joints would be painful every time we moved.

Where is cartilage found?

Tip of the nose
Outer ear (pinna)
Between bones in joints (as cushioning)
Between vertebrae (the small bones of the spine)
Trachea (windpipe) — the rings that keep it open

Joints — Where Bones Meet

A joint is the place where two or more bones meet. Joints are what make movement possible. If our skeleton were one solid piece, we couldn’t bend, twist, or move at all.

Different joints allow different kinds of movement. We have four main types:

1. Ball-and-Socket Joint

Imagine a ball sitting inside a cup. The ball can rotate in any direction inside the cup. That is exactly how a ball-and-socket joint works.

Examples: Shoulder joint (arm meets shoulder), hip joint (leg meets pelvis).

Movement allowed: In all directions — forward, backward, sideways, and rotation. This is the most flexible type of joint.

Try this: Stretch your arm out and swing it in a full circle. You can do that because of the ball-and-socket joint at your shoulder!

Remember: Ball-and-socket = shoulder and hip. These joints allow the most movement (all directions).

2. Pivotal Joint (Pivot Joint)

A pivot joint allows rotation — it lets one bone turn or twist around another.

Example: The joint where the skull meets the backbone (the atlas and axis vertebrae in the neck).

Movement allowed: Rotation only. You can shake your head left and right (“no, no”) because of this joint.

Try this: Say “no” by shaking your head side to side. That rotation at the top of your neck is your pivot joint at work!

3. Hinge Joint

A hinge joint works exactly like a door hinge — it opens and closes in one direction only.

Examples: Elbow joint (upper arm meets forearm), knee joint (thigh meets lower leg), ankle joint.

Movement allowed: Back and forth (bending and straightening) in one plane only — like a door that swings open and shut.

Try this: Bend and straighten your elbow. It only goes one way — that’s the hinge joint!

A good trick: Hinge joint = door hinge = one direction only. If you can move a joint in all directions, it is a ball-and-socket. If it only bends one way, it is a hinge.

4. Fixed Joint (Immovable Joint)

Some joints do not move at all. These fixed joints hold bones together firmly without allowing any movement.

Example: The bones of the skull. Our skull is made of several flat bones that are fused together. The lines where they meet are called sutures.

Why no movement? The skull needs to protect the brain completely. If skull bones could shift around, even a small knock could damage the brain. Fixed joints make the skull a solid, protective helmet.

Newborn babies actually have soft spots on their skull called fontanelles — gaps where the skull bones haven’t fully fused yet. This helps the baby’s head to squeeze through during birth. By about age 2, these close up completely.

Summary of Joint Types

Joint Type	Movement	Example
Ball-and-Socket	All directions + rotation	Shoulder, Hip
Pivot	Rotation only	Neck (head turns side to side)
Hinge	Back and forth (one plane)	Elbow, Knee
Fixed	No movement	Skull bones

The Backbone (Spine / Vertebral Column)

The backbone is not one long bone — it is a column of 33 small bones called vertebrae (singular: vertebra). They are stacked on top of each other like a pile of coins.

Between each pair of vertebrae there is a disc of cartilage. This cushions the bones and also lets the spine bend and twist. That is why we can touch our toes (spine bends forward) and look over our shoulder (spine rotates).

The backbone also has a hollow canal running through it called the vertebral canal — this is where the spinal cord is safely protected.

Backbone is made of 33 vertebrae (small bones). The cartilage discs between them act as shock absorbers and allow the spine to bend. This is a common fill-in-the-blank question.

The Rib Cage

Count your ribs by pressing your fingers along the sides of your chest — you’ll feel a row of curved bones. These are your ribs, and together with the breastbone (sternum) they form the rib cage.

We have 12 pairs of ribs (24 ribs total):

True ribs (1–7): Connected directly to the breastbone by cartilage at the front.
False ribs (8–10): Connected to the 7th rib cartilage, not directly to the breastbone.
Floating ribs (11–12): Not connected to the breastbone at all — they “float” free at the front.

Why is the rib cage important?

It protects the heart and lungs.
It moves up and down during breathing — helping air fill and leave the lungs.

How Animals Move

Different animals have very different body structures, and each one moves in a way that suits its body and habitat.

Earthworm

An earthworm has no bones or legs! It moves by using two sets of muscles:

Circular muscles — when these contract, the worm becomes long and thin
Longitudinal muscles — when these contract, the worm becomes short and fat

The worm also has tiny hair-like bristles called setae on its body that grip the soil and stop it from sliding back.

Movement: The front stretches forward, grips, then the back is pulled forward. Repeat. This is called peristaltic movement.

Snail

A snail has a single, large muscular organ called the foot. It contracts and relaxes in waves to push the snail forward. The snail also produces mucus (a slimy liquid) which reduces friction and helps it glide smoothly — even over rough surfaces like rocks.

Fish

Fish are perfectly shaped for moving through water:

Their body is streamlined (smooth and tapered at both ends) — this reduces water resistance.
They have fins (pectoral fins for steering, dorsal fin for balance, tail/caudal fin for pushing forward).
They have a flexible spine — the body bends from side to side, pushing the tail fin to propel the fish forward.
A special organ called the swim bladder (an air-filled sac) helps them float at different depths without sinking or rising.

Streamlined body shape = less water resistance = faster movement. Sharks, dolphins, and submarines all use this principle!

Bird

Birds are built for flying:

Wings are modified forelimbs. They are shaped like an aerofoil (curved on top, flat below) — this creates lift when air moves over them.
Hollow bones — bird bones are lightweight because they are hollow inside. Less weight = easier to fly.
Powerful chest (pectoral) muscles — these attach to the breastbone and provide the force to flap wings.
Streamlined body — feathers smooth out the surface to reduce air resistance.

Not all birds fly — penguins use their wings as flippers for swimming, and ostriches have tiny wings used for balance while running.

Snake

Snakes have no legs — they move using their backbone and muscles in a technique called slithering (also called serpentine movement).

A snake’s backbone has hundreds of vertebrae (as many as 300–400!), making it very flexible. The snake pushes its body against the ground in S-shaped curves. The scales on its belly grip the ground, and the muscles contract in waves to move it forward.

Snakes cannot move on perfectly smooth glass — their scales have nothing to grip!

Summary: How Animals Move

Animal	Body Feature Used	Type of Movement
Earthworm	Circular + longitudinal muscles, setae	Peristaltic (stretch and contract)
Snail	Muscular foot + mucus	Gliding
Fish	Streamlined body, fins, flexible spine	Swimming
Bird	Wings, hollow bones, strong chest muscles	Flying
Snake	Hundreds of vertebrae, belly scales	Slithering

5 Common Mistakes Students Make

Mistake 1: Saying the neck has a hinge joint.

The neck has a pivot joint, not a hinge joint. The pivot joint lets you rotate your head side to side (saying “no”). A hinge joint only bends — like your knee or elbow. The joint that lets you nod up and down (saying “yes”) is a different joint — but the turning movement is the pivot joint. In NCERT exams, the neck is listed as the example for pivot joint.

Mistake 2: Thinking cartilage and bone are the same thing.

Cartilage is softer and more flexible than bone. You can bend the tip of your nose or ear because they are cartilage, not bone. Bone is hard and cannot bend. Both are types of connective tissue, but they have different properties and locations.

Mistake 3: Saying the skull has no joints.

The skull does have joints — they are fixed joints (also called immovable or fibrous joints). The sutures (lines on the skull) are where the skull bones are fused. Joints do not have to allow movement. Fixed joints hold bones together without allowing movement.

Mistake 4: Saying fish use only their fins to swim.

Fish use their entire body — the backbone bends from side to side, and the whole body curves. The tail fin provides the main push (thrust) forward. Fins help with steering and balance, but the S-shaped body movement is the main swimming force.

Mistake 5: Thinking birds have solid heavy bones.

Birds have hollow bones to reduce weight for flight. Hollow does not mean weak — the bones have internal struts (like a bridge) that keep them strong while staying light. This is a very common NCERT question.

Practice Questions

Q1. What are the three main functions of the human skeleton?

The skeleton has three main functions:

Support: The skeleton is the internal framework that holds the body upright and gives it shape. Without bones, we would be like a soft blob.
Protection: Bones protect delicate organs. The skull protects the brain, the rib cage protects the heart and lungs, and the vertebral column protects the spinal cord.
Movement: Bones act as levers. Muscles are attached to bones, and when muscles contract, they pull on bones to produce movement at the joints.

Q2. Name the four types of joints in the human body. Give one example of each.

The four types of joints are:

Ball-and-socket joint — allows movement in all directions. Example: shoulder joint and hip joint.
Pivot joint — allows rotation only. Example: the joint between the skull and the first vertebra of the neck (lets you shake your head side to side).
Hinge joint — allows movement in one direction (like a door hinge). Examples: elbow joint and knee joint.
Fixed joint (immovable joint) — allows no movement. Example: the joints between the bones of the skull (sutures).

Q3. What is the difference between bone and cartilage? Give two examples of where cartilage is found.

Bone is hard and rigid. It is made of calcium and phosphorus, which give it strength. Bones cannot bend.

Cartilage is softer and more flexible than bone. It can bend without breaking.

Two examples of where cartilage is found:

Tip of the nose — it is soft and can be bent
The outer ear (pinna) — firm but flexible

Q4. An earthworm has no legs. How does it move?

An earthworm moves by using two sets of muscles:

Circular muscles: When these contract, the worm becomes long and thin.
Longitudinal muscles: When these contract, the worm becomes short and fat.

The worm stretches its front part forward, anchors itself using tiny bristles called setae, and then pulls the back part forward. This cycle repeats continuously. This type of movement is called peristaltic movement.

Q5. Why are a bird’s bones hollow? Does this make them weak?

A bird’s bones are hollow to reduce the bird’s overall body weight. Less weight means less energy is needed to flap wings and stay airborne — so hollow bones are an adaptation for flight.

Hollow bones are NOT weak. Inside the hollow bones there are thin struts or supports (like the cross-supports inside a bridge) that keep the bone strong even though it is hollow. So birds get the benefit of light weight without losing strength.

Q6. What is a streamlined body shape? Why is it useful for fish?

A streamlined body is smooth, rounded at the front, and tapering toward the back (like a torpedo or teardrop shape). This shape offers the least resistance when moving through water or air.

Fish have streamlined bodies, which means water can flow smoothly around them with very little drag (resistance). Less resistance means the fish can swim faster and use less energy. This is why fast-swimming fish like sharks and tuna have very sleek, streamlined bodies.

Q7. What is the rib cage? Name its two main functions.

The rib cage is a bony structure made of 12 pairs of ribs and the breastbone (sternum). It forms a protective cage around the chest area.

Two main functions:

Protection: It protects the heart and lungs from injury.
Breathing: The rib cage moves up and outward when we inhale, increasing the volume of the chest cavity so air can rush into the lungs. It moves down and inward when we exhale.

Q8. How does a snake move even though it has no legs?

A snake moves by slithering, also called serpentine locomotion.

A snake has a very flexible backbone made of hundreds of tiny vertebrae (between 100 and 400 depending on the species). Strong muscles attached to these vertebrae allow the snake to bend its body into S-shaped curves.

When the snake pushes the curved parts of its body against the ground or any surface, the ground pushes back, propelling the snake forward. The scales on the snake’s belly grip the surface to prevent slipping backward. The whole body moves in a smooth wave from head to tail.

Frequently Asked Questions

How many bones does a human body have?

An adult human body has 206 bones. Interestingly, babies are born with about 270–300 bones. As we grow, many of these bones fuse together. For example, the skull bones fuse during the first two years of life.

What is the longest bone in the human body?

The femur (thigh bone) is the longest and strongest bone in the human body. It runs from the hip to the knee.

Why do joints hurt when we get older?

Joints are cushioned by cartilage — a smooth, rubbery material. Over time, this cartilage can wear away. Without this cushion, bones start rubbing against each other, causing pain and inflammation. This condition is called arthritis.

What is the difference between the shoulder joint and the knee joint?

The shoulder is a ball-and-socket joint that can move in all directions (you can swing your arm in a full circle). The knee is a hinge joint that can only bend and straighten in one direction (like a door hinge). The shoulder has more freedom of movement but is more prone to dislocation; the knee is more stable.

Can cartilage grow back if it is damaged?

Cartilage has very poor ability to heal itself because it has no blood vessels running through it. Blood vessels bring repair cells and nutrients. Without them, damaged cartilage heals very slowly and sometimes not at all. This is why knee cartilage injuries take so long to heal.

Why does a snail need mucus to move?

The snail’s muscular foot pushes against the ground in a wave motion. Mucus (a slippery fluid produced by the foot) reduces friction between the foot and the surface. Without mucus, the rough foot would create too much friction and the snail could not glide smoothly. Mucus also helps the snail stick to vertical surfaces and even hang upside down.