THE EAR
It is an organ for hearing and maintenance of body equilibrium It is controlled by the brain through the eighth cranial nerve called vestibulocochlear nerve The ear is divided into three parts :
1.External or outer ear
2.Middle ear or tympanic cavity
3.Internal or inner ear
External Ear ::
It consists of pinna which helps to collect the sound waves and the external auditory meatus which conveys the sound waves from the pinna to the tympanic membrane Pinna is made up of flexible cartilagenous material and weak muscles The auditory canal or External meatus is 3 cm long its inner part is closed by a thin membrane called drum of the ear or tympanic membrane Hair and wax are present near its outer part to arrest dust particles This cannal conveys sound waves to the drum
fig external ear
Middle Ear ::
It is a small chamber internal to the drum and contains air It is made up of bone and a membranous wall The eustaschian tube continues from the middle ear and opens in the nasopharynx so that air pressure is maintained in equilibrium on either side of the drum The mastoid antrum also opens in the middle ear
fig middle ear
There are three small delicate bony structures (ossicles) situated across the middle ear The hammer shaped bone is called malleus Its handle is attached to the tympanic membrane and the handle projects into the tympanic cavity The middle bone is known as the Incus which connects with the malleus on its outer side and stapes on its inner side The third bone is stapes which joins with the incus These three bones send the vibrations of sound from the drum to the internal ear
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