CBSE Class 5 Science Sense Organs and the Nervous System Notes Set 01

How we know our surroundings

We learn about the world by seeing, hearing, smelling, tasting and touching. The parts of the body that collect this information are called sense organs. The five sense organs are the eyes, ears, nose, tongue and skin. They send messages through nerves to the brain, which is part of the nervous system, and the brain tells us what the message means.

Eyes (sense of sight)

1. Most of what we learn about our surroundings comes through the eyes. 2. Eyelids and eyelashes protect the eye from dust, strong light and injury. 3. A clear covering called the cornea protects the front of the eye. 4. The iris is the coloured part and decides the colour of our eyes. 5. Light enters through a small opening in the middle of the iris called the pupil. 6. The lens lies behind the iris and focuses the light. 7. The retina is a thin layer at the back of the eye that catches the light and turns it into signals. 8. The optic nerve carries these signals to the brain.

Nose (sense of smell)

The nose helps us smell and breathe. It has two openings called nostrils, separated by a wall called the nasal septum. The shape of the nose is given by bone and cartilage. When air enters the nose, it touches nerve endings called olfactory nerves, which send signals to the brain, and the brain identifies the smell.

Ears (sense of hearing)

The outer part of the ear that we can see is called the pinna. It collects sound and sends it to the eardrum. The eardrum vibrates when sound strikes it and passes the vibrations through the middle ear to the inner ear. A special nerve carries the message to the brain, which understands it as sound.

Tongue (sense of taste)

The tongue is a fleshy organ that helps us speak, chew and taste. Its surface has thousands of taste buds with nerve endings that send messages to the brain. The tongue can tell four basic tastes: sweet, salty, sour and bitter.

Skin (sense of touch)

Skin is the largest organ of the body and covers it completely. It protects the organs inside, helps heal wounds, keeps out germs and helps control body temperature. It has millions of nerve endings that sense heat, cold, pain and pressure.

Taking care of sense organs

1. Do not rub your eyes with dirty hands, and read in good light. 2. Never put sharp objects into your ears or nose. 3. Avoid very loud sounds. 4. Wash and keep your skin clean.

Worked examples

Example 1. Which organ senses that a cup of tea is hot? Answer: The skin, because its nerve endings sense heat and send the message to the brain.

Example 2. Trace how we see a flower. Answer: Light from the flower enters the pupil, the lens focuses it on the retina, and the optic nerve carries the signal to the brain.

Example 3. Why can we not taste food well when we have a bad cold? Answer: A blocked nose weakens the sense of smell, and taste and smell work together to give the flavour of food.

Quick Check Questions