CBSE Class 6 Science — Body Movements

Introduction to Body Movements

All living organisms exhibit movement. When an entire organism shifts from one place to another, it is called locomotion. To make these movements possible, the human body uses a complex framework of bones and joints.

Joints in the Human Body

Places where two or more bones meet are called joints. Different joints allow different types and degrees of movement.

graph TD
    Joints --> Immovable["Immovable / Fixed Joints (e.g., Skull)"]
    Joints --> Movable["Movable Joints"]
    Movable --> BallAndSocket["Ball and Socket Joint"]
    Movable --> Pivotal["Pivotal Joint"]
    Movable --> Hinge["Hinge Joint"]
    Movable --> Gliding["Gliding Joint"]

Types of Movable Joints

1. Ball and Socket Joint:

   • Allows movement in all directions.
   • The rounded end of one bone fits into the hollow space (socket) of another.
   • Examples: Shoulder joint, Hip joint.

2. Pivotal Joint:

   • Allows forward, backward, left, and right movement.
   • A cylindrical bone rotates in a ring.
   • Example: The joint where our neck joins the head.

3. Hinge Joint:

   • Allows movement only in one plane (like a door hinge).
   • Examples: Knee joint, Elbow joint.

4. Gliding Joint:

   • Bones glide past each other.
   • Examples: Bones of the wrist and ankle.

The Human Skeleton

The framework of bones that gives shape, support, and protection to our internal organs is the skeleton. A human skeleton comprises 206 bones (an adult).

Key Parts:

• Skull: Protects the brain. Upper jaw is fixed; lower jaw is movable.
• Rib Cage: 12 pairs of ribs joined to the chest bone and backbone. Protects heart and lungs.
• Backbone: Consists of 33 small bones called vertebrae. Protects the spinal cord.
• Pelvic Bones: Encloses the portion below the stomach and helps us sit.
• Cartilage: Some parts of the skeleton are not as hard as bones and can be bent. They are called cartilages (e.g., earlobe, nose tip, between vertebrae).

How do Muscles Help in Movement?

Muscles work in pairs. When a muscle contracts, it becomes shorter, stiffer, and thicker, pulling the bone. A muscle can only pull; it cannot push. Thus, to move the bone back, the opposite muscle in the pair must contract while the first one relaxes.

Gait of Animals (How Animals Move)

Animals move in fascinating ways without having bones like humans.

1. Earthworm

• Has no bones. Its body is made of many rings joined end to end.
• Has muscles that help extend and shorten the body.
• Small bristle-like structures under its body grip the ground.

2. Snail

• Covered by a hard, single shell (exoskeleton), which does not help in moving but has to be dragged along.
• Moves using a thick structure called the muscular foot.

3. Cockroach

• Has an outer skeleton (exoskeleton).
• Three pairs of legs (for walking) and two pairs of wings attached to the breast. Strong muscles help it fly and walk.

4. Birds

• Bones are hollow and light (pneumatic bones), making them fit for flying.
• Forelimbs are modified into wings.
• Strong breast muscles help flap the wings.

5. Fish

• Have a streamlined body shape (tapering at ends) which allows water to flow easily around it.
• Fins help in maintaining balance and changing direction.
• The tail sweeps side to side to push the fish forward.

6. Snakes

• Have a long backbone, thin muscles, and no legs.
• They move by looping their body into curves. Each loop pushes against the ground to thrust the snake forward (slithering).