The special senses

 The special senses .

There are five sense organs with special senses which are listed below: 

                          

* Eye - to see

* Ear - to hear

* Nose - to smell

* Tongue - to taste

* Skin - to touch

The eye 

    Eye are two in number.it is very precious and delicate organ.each eye is protected in the orbital cavity of the skull with a pad of fat behind.

                          

Accessory organs help to protect the eyes which are: 

* Eyebrow- it protects from too much light and sweat of the forehead.

*  Eyelids- upper and lower- each with a row of eyelashes on the edge- help to keep dust and insects away.

* Conjunctiva- layer of mucous membrane which lines the eyelid.

* Tear gland and ducts- tears from tear gland in the upper outer corner of the eye wash over the front of the eye- keeps it moist and clean.excess of tear is removed by tear duct into the nose.

* Muscles of eyeball- the eyeball is attached to the bony orbit by six muscles.they work in harmony to move the eyeball up and down. Side to side and obliquely.

The Ear

The ear consists of following parts: 

* The external ear.

*The middle ear.

* The internal ear.

* The audiotory nerve and hearing center in the brain.

                                 

The external ear

                      

It consists of: 

* Pinna - the part which is attached to the side of head.its function is to collect sound and direct them inside the ear.
*  Auditory canal- a curved tube 3cm .long leading to the eardrum. It protects the eardrum from insects and foreign bodies.
* Eardum - it is a membrane  attached across the hole in the bone.when sound waves hit it, eardrum vibration.it is perforated- deafnessmay occcur

                             The middle ear.

 

                           

It is a tiny cavity filled with air inside the temporal bone.the muddle ear is lined with mucous membrane and connected by eustactrian tube with upper part of throat.

                                   The internal ear: 

                               

If is also inside the temporal bone,but it is filled with fluid

The parts of internal ear are:  

*  Cochlea- it looks like the shell of a small snail.it contains nerve endings for hearing.

* Vestibule-  a small cavity behind the oral window.

* Semicircular canals- curving upward, backward and sideways,all connected with the vestibule.fluid in this canal  moves as we change our position.this helps to keep our balance.

 

                               The audiotory nerve

                                

This takes the messages from the internal ear to the centres for hearing and balance in the brain.

                The mechanism of hearing

Sound waves are collected by the pinna pass along the auditory canal and set the eardrum in vibration.these vibrations are transmitted across the middle ear by movement of small three bone to the membrane of oral window.

These vibrations cause movement of fluid in the cochlea the nerve endings in the cochles are stimulated and messages are conveyed to the auditory nerve to the brain and sensation of hearing is interpreted.

           The senses of small and teste

Smell is conveyed to the brain by the olfactory nerve.olfactory nerve endings are situated in the upper part of the nose and help in getting the smell.

Taste is one of the functions of the toungue.the taste buds are located in the rough surface of the tongue.the nerve endings are in these taste buds.different taste buds are for different taste sensation s- which are;

Sweet

Sour

Bitter,and salt.