Give The Role Of Tympanic Membrane

The middle ear is located in the tympanic cavity of the temporal bone. It begins with the eardrum, or tympanic17 membrane, which closes the inner end of the auditory canal and separates it from the middle ear. The membrane is about 1 cm in diameter and slightly concave on its outer surface. It is suspended in a ring-shaped groove in the temporal bone and vibrates freely in response to sound. It is innervated by sensory branches of the vagus and trigemi-nal nerves and is highly sensitive to pain.

17 tympan = drum

Auricle Pinna The Ear Mcgraw Hill
Figure 16.9 Anatomy of the Auricle (pinna) of the Ear.

Posteriorly, the tympanic cavity is continuous with the mastoidal air cells in the mastoid process. It is filled with air that enters by way of the auditory (eustachian18) tube, a passageway to the nasopharynx. (Be careful not to confuse auditory tube with auditory canal.) The auditory tube is normally flattened and closed, but swallowing or yawning opens it and allows air to enter or leave the tympanic cavity. This equalizes air pressure on both sides of the eardrum and allows it to vibrate freely. Excessive pressure on one side or the other dampens the sense of hearing. The auditory tube also allows throat infections to spread to the middle ear.

The tympanic cavity, a space only 2 to 3 mm wide between the outer and inner ear, contains the three smallest bones and two smallest skeletal muscles of the body. The bones, called the auditory ossicles,19 connect the eardrum to the inner ear. Progressing inward, the first is the malleus,20 which has an elongated handle attached to the inner surface of the eardrum; a head, which is suspended from the wall of the tympanic cavity; and a short process, which articulates with the next ossicle. The second bone, the incus,21 articulates in turn with the stapes22 (STAY-peez). The stapes has an arch and footplate that give it a

,8Bartholomeo Eustachio (1520-74), Italian anatomist

20malleus = hammer

21 incus = anvil

22stapes = stirrup

Saladin: Anatomy & I 16. Sense Organs I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 16 Sense Organs 599

K Ossicles

Stapes

Helix

Auricle

Tympanic — membrane Auditory— canal

Earlobe r 1

Outer ear

K Ossicles

Stapes

Tympanic — membrane Auditory— canal

Tympan Short Process

Semicircular ducts

Vestibular nerve Cochlear nerve

Cochlea

Round window Tympanic cavity

Tensor tympani muscle

Auditory tube r 1

Outer ear

Middle ear

Inner ear

Figure 16.10 Internal Anatomy of the Ear.

Semicircular ducts

Vestibular nerve Cochlear nerve

Cochlea

Round window Tympanic cavity

Tensor tympani muscle

Auditory tube

Middle ear

Inner ear

Figure 16.10 Internal Anatomy of the Ear.

shape like a stirrup. The footplate, shaped like the sole of a steam iron, is held by a ringlike ligament in an opening called the oval window, where the inner ear begins.

The muscles of the middle ear are the stapedius and tensor tympani. The stapedius (stay-PEE-dee-us) arises from the posterior wall of the cavity and inserts on the stapes. The tensor tympani (TEN-sor TIM-pan-eye) arises from the wall of the auditory tube, travels alongside it, and inserts on the malleus. The function of these muscles is discussed under the physiology of hearing.

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