Hearing is a complex and intricate process. The ear is made up of three sections: the outer ear, the middle ear, and the inner ear. These parts work together so you can hear and process sounds. The outer ear, or pinna (the part you can see), picks up sound waves and directs them into the outer ear canal.

These sound waves travel down the ear canal and hit the eardrum, which causes the eardrum to vibrate. When the eardrum vibrates, it moves three tiny bones in your middle ear. The middle ear is a small air-filled space between the eardrum and the inner ear. These bones form a chain and are called the hammer (or malleus), anvil (or incus), and stirrup (or stapes). The movement of these bones transmits and amplifies the sound waves toward the inner ear.

The third bone in the chain, the stapes, interfaces with fluid that fills the hearing portion of the inner ear -- the cochlea. The cochlea is lined with cells that have thousands of tiny hairs on their surfaces. As the fluid wave travels through the cochlea, it causes the tiny hairs to move. The hairs change the mechanical wave into nerve signals. The nerve signals are then transmitted to your brain, which interprets the sound.

Symptoms of hearing loss may include:

• Certain sounds seem too loud

• Difficulty following conversations when two or more people are talking

• Difficulty hearing in noisy areas

• Hard to tell high-pitched sounds (such as "s" or "th") from one another

• Less trouble hearing men's voices than women's voices

• Problems hearing when there is background noise

• Voices that sound mumbled or slurred

• Feeling of being off-balance or dizzy (more common with Meniere's disease and acoustic neuroma )

• Pressure in the ear (in fluid behind the eardrum)

• Ringing or buzzing sound in the ears ( tinnitus )

Conductive hearing loss (CHL) occurs because of a mechanical problem in the outer or middle ear. Causes of conductive hearing loss can often be treated. They include:

• Buildup of wax in the ear canal

• Damage to or fixation of the very small bones (ossicles) that are right behind the eardrum

• Fluid that stays in the ear after an ear infection

• Foreign object that is stuck in the ear canal

• Hole in the eardrum

• Scar on the eardrum from repeat infections

Sensorineural hearing loss (SNHL) occurs when the hearing nerve or the tiny hair cells (nerve endings) that detect sound in the ear are injured, diseased, do not work correctly, or have died. This type of hearing loss often cannot be reversed.

Sensorineural hearing loss is commonly caused by:

• Acoustic neuroma

• Age-related hearing loss

• Childhood infections, such as meningitis, mumps, scarlet fever, and measles

• Meniere's disease

• Regular exposure to loud noises (such as from work or recreation)

• Use of certain medicines

• Birth defects which cause changes in the ear structures

• Genetic conditions (more than 400 are known)

• Infections the mother passes to her baby in the womb (such as toxoplasmosis, rubella, or herpes)

• Pressure differences between the inside and outside of the eardrum, often from scuba diving

• Skull fractures (can damage the structures or nerves of the ear)

• Trauma from explosions, fireworks, gunfire, rock concerts, and earphones

Tests that may be done include:

• Audiometry(a hearing test used to check the type and amount of hearing loss)

• CTor MRI scan of the head (if a tumor or fracture is suspected)

• Tympanometry

Surgical:

• Eardrum repair

• Placing tubes in the eardrums to remove fluid

• Repair of the small bones in the middle ear (ossiculoplasty)

• Stapedectomy for otosclerosis

• Canalplasty for narrowed ear canal

Non-surgical:

• Devices for hearing loss

• Hearing aids