CHAPTER 3

THE EAR

To understand Eustachian Tube Irritation it is helpful to understand the function of the middle ear [ME] and Eustachian tube [ET] and the differences between their level of development in the adult and the child. Such an understanding shows why infants and children are more prone to ETI.

OUTER EAR

The outer ear consists of the pinna, ear lobe and the outer ear canal. In animals, the pinna turns towards a sound to direct the sound into the ear canal but this function has been lost in humans. The outer ear canal ends at the ear drum [tympanic membrane].

The outer ear canal is lined with skin. There are hairs along the canal. Glands near the ear drum secrete wax. The drum is protected by its depth along the ear canal and by the hairs and wax. The wax moves along the canal mixed with skin cells that desquamate [lift off the skin] and any other debris that has collected, until it reaches the outer end of the canal where it drops out of the canal.


MIDDLE EAR

The middle ear [ME] starts at the ear drum. The ear drum is a very sensitive structure—supplied with pain sensitive nerves. Behind the drum is an air-filled cavity called the middle ear cavity. Inside the middle ear cavity are three tiny bones—the ossicles [the malleus, incus and stapes]. Leading from the middle ear cavity to the back of the nose/throat is the Eustachian tube [ET]. This has a narrow area, called the isthmus, near where it enters the middle ear.

INNER EAR

The inner ear is enclosed in dense bone. It comprises the vestibular apparatus [organ of balance] and the cochlear [organ of hearing]—with the nerves from these going to the brain.


STRUCTURE & FUNCTION OF THE MIDDLE EAR [ME] & EUSTACHIAN TUBE [ET]

The ME cavity is lined by several types of cells. Some of the cells produce mucus and some have tiny fronds [called ‘cilia’] that wave towards the ET. When healthy, the middle ear cavity is filled with air at atmospheric pressure—the same pressure as in the outer ear canal. The pressure in the ME cavity is maintained by air coming into the middle ear from the throat via the ET.

The ET is critical for normal function of the ME.

The ET opens and closes by the action of small muscles attached near its opening into the nasopharynx. It closes during swallowing to prevent food or fluid entering the middle ear and….


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Schematic of the ear