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Eardrum

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The eardrum is a vital part of the human auditory system. It is also known by the scientific names tympanic membrane or myringa. This thin, cone-shaped membrane sits between the external ear and the middle ear. Its primary job is to capture sound waves from the air. It then transmits those changes in air pressure to the middle ear. This process allows the ear to convert air vibrations into vibrations in the cochlear fluid. Without this membrane, the body could not properly process sound.

To understand how hearing works, we must look at the mechanical process. Sound creates changes in air pressure that hit the membrane. This causes the eardrum to vibrate. The malleus, or hammer bone, is firmly attached to the medial surface of the membrane. This bone acts as a bridge between the eardrum and the other ossicles. The ossicles are the tiny bones located inside the middle ear. These bones move the vibrations toward the oval window. The oval window is an opening into the fluid-filled cochlea. This chain reaction amplifies the vibration so the inner ear can detect it.

The structure of the eardrum is not uniform. It is divided into two distinct regions: the pars flaccida and the pars tensa. The pars flaccida is a small, relatively fragile area located at the top. It sits above the lateral process of the malleus. This region consists of two layers and often has a pinkish hue. The larger region is called the pars tensa. It is much more robust because it contains three layers. These layers include skin, fibrous tissue, and mucosa. The edge of the pars tensa is a thick ring called the annulus tympanicus. This ring is also known as Gerlach's ligament.

Specific anatomical features help define the shape of the membrane. The handle of the malleus, or manubrium, is attached to the membrane. This attachment pulls the membrane toward the tympanic cavity. Because of this pull, the lateral surface of the membrane is concave. The deepest part of this concavity is called the umbo. The membrane also sits at an oblique angle. It is positioned between several important structures. It relates to the middle cranial fossa above and the parotid gland below. It also sits near the facial nerve and the temporomandibular joint.

Because the eardrum is a sensory organ, it is supplied by several nerves. The outer surface receives sensation from the auriculotemporal nerve. This nerve is a branch of the mandibular nerve, also called cranial nerve V3. Other contributors to the outer surface include the facial nerve and the vagus nerve. The inner surface of the membrane is innervated by the glossopharyngeal nerve. This nerve is also known as cranial nerve IX. These nerves allow the body to sense various stimuli within the ear canal.

Medical professionals often examine the eardrum to check for health issues. When a doctor shines a light into the ear, they look for a specific sign. A cone of light should radiate from the tip of the malleus. This light typically reaches the periphery in the anteroinferior quadrant. Clinicians refer to this specific light pattern as the "5 o'clock" position. If the eardrum is ruptured or perforated, it can lead to conductive hearing loss. A rupture might also cause tinnitus, which is ringing in the ears, or vertigo. Vertigo is a feeling of disequilibrium or dizziness.

Injuries to the eardrum can happen in many ways. Unintentional ruptures often occur due to blast injuries or changes in air pressure during travel. This is common in people with Eustachian tube dysfunction. Such dysfunction prevents the ear from equalizing pressure. Other causes include swimming, scuba diving, or martial arts. While some ruptures are serious, many heal on their own. Between 80 and 95 percent of ruptures recover completely within two to four weeks. In some cases, doctors perform a myringotomy. This is a surgical procedure where a tiny incision is made to drain fluid or pus. This is often done to treat otitis media, a common middle ear infection in children. To prevent fluid from building up again, a tympanostomy tube may be inserted. Without a tube, the incision usually heals in two to three weeks. These tubes are either removed by a doctor or fall out naturally within 6 to 12 months.

Cultural practices can also impact the eardrum. The Bajau people of the Pacific have a unique relationship with this anatomy. They intentionally rupture their eardrums at an early age. They do this to help them with deep-sea diving and hunting. Because of these intentional ruptures, many older Bajau people have difficulty hearing. This shows how the physical state of the eardrum can change a person's way of life.

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