Grade 3 science (NSO) : Human body part 3

Links to part 1 and part 2 of the human body

Grade 3 Science (NSO) : Human body part 1

Grade 3 Science(NSO) : Human body part 2

Nervous system

This system controls all our actions, sense of feelings and thinking is called Nervous system.The nervous system is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. It is essentially the body’s electrical wiring.

  • It consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body
  • Brain is the most vital organ of our body
  • It sends and receives messages to and from all parts of the body through nerves
  • Spinal chord is the bundle of nerves that runs up and down the center of the back; connects the brain to the nerves; carries signals between the brain and other parts of the body
  • The brain and spinal cord form the control center known as the central nervous system (CNS).

  • The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS


Endocrine system

The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

The endocrine system is made up of the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries (in females) and testicles (in males)

Reproductive system

The reproductive system is a collection of internal and external organs — in both males and females . It helps to produce young ones. Due to its vital role in the survival of the species, many scientists argue that the reproductive system is among the most important systems in the entire body.

Important words in human body

Cell :

Building block of our body. Your body is made up of trillions of tiny cells, which are the basic units of life–the smallest building blocks of a living thing.

Tissue :

A tissue is a group of similar cells that all work together on the same job.

Organ :

Organs are collections of tissues with similar functions. In higher animals, organs are grouped into organsystems; e.g., the esophagus, stomach, and liver are organs of the digestive system.

Circulatory System

Blood vessels :

Thin tubes through which blood flows.

Arteries :

Arteries, which usually look red, are blood vessels that carry blood away from the heart to all the parts of your body They have very thick walls which allow them to withstand the immense pressure created as your heart pumps blood forcefully. As blood travels outward, the arteries become smaller and smaller until eventually the blood enters into what are known as capillaries.

Capillaries :

Capillaries are so tiny that blood usually can only get through one cell at a time. It is within the capillaries that oxygen is taken in by the cells, and waste, such as carbon dioxide, is released into the blood.Eventually the capillaries get bigger and bigger, and then the blood enters into veins. As the blood travels back to the heart your veins get larger and larger.

Veins :

Veins, which usually look blue, are blood vessels that return blood to the heart.

Muscular system

Tendon :

Strong tissue that joins muscles to the bones.

Nervous system

Nerves :

Fibre-like structures in the body that transmits messages to the brain.

Digestive system

Pancreas :

Part of the digestive system that secretes juices that digest fats and protein.

Liver :

Part of the digestive system that secrete bile, which helps absorb fats.

Gall bladder :

Part of the digestive system that stores extra bile.

Respiratory system

Pharynx :

Part of the respiratory system, pharynx, or throat, is part of the passage (or tube!) that air will go down to enter our lungs.

Larynx :

Part of the respiratory system ,the voice box, another part of our main air passage.

Trachea :

The windpipe is a long tube that goes down our neck to the lungs. There is also cilia in the windpipe. The windpipe’s lining makes mucus, which traps dust and other dirt particles. Cilia brings this mucus towards our throat, where we swallow and digest it.

Bronchi and Bronchioles

Tubes that branch from the trachea into our lungs. The bronchioles make a tree-like structure in the lungs so air can reach every corner.


Two spongy organs in our chest. Lungs have a lot of little air sacs called alveoli. Tiny blood capillaries run through alveoli. When air reaches the alveoli, it passes into the bloodstream. It is then carried around our entire bodies.


The main muscle in the respiratory system. The diaphragm stretches out underneath the lungs. When it contracts, it expands outwards. This makes more space inside our chest for air to rush in. When the diaphragm relaxes, it moves inwards. This decreases the space inside our chest and pushes air out.