1 external ear , middle ear and clinical case

The ear contains a series of receptors specialized for hearing and equilibrium. It is formed of:
1- The external ear.
2- The middle ear (the tympanic cavity).
3- The internal ear (the labyrinth).
I) The external ear
It consists of three parts:
1- The auricle (ear pinna):
It is a funnel-like plate of yellow elastic cartilage covered by skin on both sides. It collects the sound waves and directs them towards the external auditory meatus. The lobule of the ear is formed of adipose C.T.
2- The external auditory meatus:
This canal leads to the middle ear. Its wall is formed of yellow elastic cartilage in its outer 1/3 and of spongy bone in its inner 2/3. It is lined by thin skin provided with stiff hairs in its outer part. The skin also contains sebaceous glands and ceruminous glands. The secretion of both glands forms the cerumen or the wax of the ear.
3- The tympanic membrane (the ear drum):
It separates the external auditory meatus form the middle ear cavity. It consists of two layers of collagenous fibres: an outer radially arranged layer and inner circularly arranged one. Both layers are covered externally by skin, and internally by simple cuboidal epithelium. The tympanic membrane transmits the vibrations of sound to the middle ear.
II) The middle ear
• It is a cavity present in the temporal bone. It contains the three auditory ossicles, 2 muscles and the chorda tympani nerve. It is lined with simple cuboidal epithelium. The middle ear (tympanic cavity) is connected to the pharynx by the eustachian tube (auditory tube). The anterior 2/3 of the wall of the eustachian tube is formed of yellow elastic cartilage and is lined with pseudostratified columnar ciliated epithelium. The posterior 1/3 of its wall is formed of spongy bone and is lined with simple columnar ciliated epithelium.
• The function of the eustachian tube is to equalize the air pressure in the tympanic cavity and the naso-pharynx.
The three auditory bony ossicles are: the malleus, the incus and the stapes arranged form the lateral to the medial side. These ossicles are formed of spongy bone. The ossicles articulate with each other by synovial joints. The handle of the malleus is attached to the tympanic membrane while the foot of the stapes closes the oval window.
The two muscles are:
 The tensor tympani muscle which is attached to the malleus.
 The stapedius muscle which is attached to the stapes.
The two windows in the medial wall of the middle ear are:
 The oval window: It is closed by the annular ligament which is attached to the foot of the stapes. Through the oval window, sound vibrations are conducted to the peri-lymph of the vestibule of the internal ear.
 The round window: It is closed by an elastic membrane called the secondary tympanic membrane which separates the middle ear form the internal ear.
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faculty of medicine
Mansoura university

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