We have five main sense

organs.The eyes

The tongue

The ears

The nose

The skin

All senses depend on the nervous system. Our sense organs start to work when something stimulates special nerve cells called receptors. The receptors send nerve impulses along the sensory nerves to the brain. Your brain then tells you what the stimulus is.

The light rays enter the eye through the cornea, which is a thick, transparent protective layer on the surface of your eye. Then the light rays pass through the pupil (the dark circle in the centre of your eye) and into the lens.

cornea

pupillens

When light rays pass through your pupil, the muscle called the iris (coloured ring) changes the size of the pupil depending on the amount of light that's available. If there is too much light, your pupil will shrink but if there is very little light available, the pupil will enlarge.

iris

The lens focuses the image onto the back surface of the eyeball, called the retina.The retina, which is the size of your thumbnail, is filled with approximately 150 million light-sensitive cells that send the information to the brain by the optic nerve.

The nose is the organ for smell.The nose has two holes called nostrils .

The nostrils and the nasal passages are separated by a wall called septum. Closer to the tip of the nose, the septum is made of cartilage, which is flexible.

When we breathe, the air goes through the nasal cavity, down the throat, into your trachea (windpipe) and your lungs.

Behind the nose, in the middle of the face, is a space called nasal cavity. It connects with the throat.

Scents or smells also travel with the air.

At the top of the nasal cavity there are some sensitive cells in the olfactory bulb that send signals along the olfactory nerve to the brain, which tell us what we smell.

olfactory bulb

olfactory nerve

nasal cavity

olfactory bulb

bone

sensitive cellsmucus

Your tongue and the roof of your mouth are covered with tiny taste buds. We have almost 10,000 taste buds inside our mouths.

When you eat something the receptor cells, located in your tastes buds, send messages through sensory nerves to your brain. Your brain then tells you what flavours you are tasting.

Your taste buds can recognize four basic kinds of tastes: sweet, salty, sour, and bitter. The salty/sweet taste buds are located near the front of your tongueThe sour taste buds line the sides of your tongueThe bitter taste buds are found at the very back of your tongue.

Choose a number for:

•Sour•Salty•Bitter•Sweet

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The ear is an organ for hearing and balance. It consists of three parts: the outer ear, the middle ear, and the inner ear.

When an object makes a noise, it sends vibrations or sound waves through the air. These vibrations are collected by the outer ear and send into the ear canal.

www.audigygroup.com

As the vibrations move into the middle ear, they hit the eardrum and makes it vibrate as well. That vibration passes to the three little bones called hammer, anvil and stirrup. Finally the vibration is transferred to the cochlea into the inner ear, and from the cochlea to the brain through the auditory nerve.

* The stirrup is the smallest bone in the human body (it is 0.25 to 0.33 cm long).

* The stirrup is the smallest bone in the human body (it is 0.25 to 0.33 cm long).

Your sense of touch is found all over the body. This is because your sense of touch originates in the bottom layer of your skin called the dermis. The dermis is filled with many tiny nerve endings which give you information about the things your body comes in contact.

The nerve endings carry the information to the spinal cord, which sends messages to the brain.The nerve endings in your skin can tell you if something is hot or cold. They can also feel if something is hurting you.

Credits:

http://library.thinkquest.org/http://dorlingkindersly.co.ukhttp://commons.wikimedia.orghttp://contenidos.educarex.es/bancoimagenes/

Published by Ana Maestro Güemes 2008