1. Lesson 19
What are sense organs?

2. The moment you were born, you started to learn
The moment you were born, you started to learn. Every instant provided you with new experiences.
You tasted, smelled, heard, felt, and saw things.

3. At first, you saw only blurred shadows
At first, you saw only blurred shadows. Day by day, the shadows cleared, and you saw perfectly, and you remembered!
You learned to recognize your mom and dad, your bottle, crib, and things in your house. Everything was new.

4. We learn and know about the world around us through our senses
We learn and know about the world around us through our senses. Humans have five major senses:
sight
hearing
taste
touch
smell

5. The sense organs are:
eyes
ears
nose
skin
tongue

6. Our senses tell us what is going on around us
Our senses tell us what is going on around us. Responses to messages from our senses help protect us and keep us alive.

7. However, the sense organs are only receptors
However, the sense organs are only receptors. They receive stimuli and send messages to the brain.
The brain interprets the messages. It is the brain that actually sees, hears, tastes, smells, and feels.

8. The Eye
Cornea: transparent “window” where light enters the eye.
Iris: circular colored part of the eye

9. Pupil: the opening in the middle of the iris that changes size depending on how much light is needed for you to see properly.
Lens: helps focus light

10. Retina: the light sensitive nerve layer in the back of the eye
Optic Nerve: leads from the retina to the brain, carrying light messages
The brain interprets the messages, and you see.

11. The ear
Sound is caused by vibrations. The vibrations travel through your ears.
Outer Ear: “catches” the sounds around you

12. Ear Canal: the tunnel the vibrations pass through to get into your body
Ear drum: a membrane that stretches across the ear canal, sound vibrations make it vibrate.

13. Ear bones: three tiny bones behind the eardrum that vibrate with sound
Cochlea: snail shaped, it changes vibrations into electrical impulses that are sent to the brain.

14. Auditory Nerve: nerve allows the electrical messages to travel to the brain
The brain interprets the messages, and you hear.

15. The Tongue
The tongue is sensitive to certain chemicals in food that allow you to taste it.

16. There are 4 different kinds of tastes:
sweet
sour
bitter
salty

17. The tongue has four kinds of receptors called taste buds.
Each kind of taste bud is sensitive to one kind of taste. They are located at different parts of the tongue.

18. The Nose
The nose is sensitive to certain kinds of chemicals. When you inhale through the nose, the air enters a space called the nasal cavity.

19. The upper part of the nasal cavity contains many odor sensitive endings. The nerve endings “pick up” odors.
All the nerve endings go to the olfactory nerve, which goes to the brain.

20. The Skin
There are senses of “feel”. Pain, heat, cold, simple touch, and pressure.
The skin has special receptors for each.
Some areas of the skin are more sensitive than others.