Causes for Hearing Disorders

The Overview of the Auditory System

The auditory is made up of many components, the outer, middle, and inner ear, cochlear nerve, auditory brainstem, and sections of the brain such as Wernicke's area or Heschel's Gyrus. All of these systems are important to the human ability to hear and each part, when correct, completes itself job of transmitting acoustic signals into bioelectric signals for the brain to interpret. All of this happens in a matter of milliseconds.

Outer/External Ear

The outer ear includes the pinna and ear canal up to the tympanic membrane. This section of ear is meant for picking up and amplifying acoustic signals to the middle ear. Because the noise being sent down the ear canal, AKA external auditory meatus, is going from a large open area into a small, tightly packed canal, the noise amplifies. This amplification can be anywhere between 1500 Hz to 8000z. This section of the ear is also built for protection against outside elements. Between producing ear wax (cerumen) and being in an 's' shape to stop insects and water flow from entering the ear, it was built with defenses against the outside world.

Middle Ear

The middle ear is made up of the tympanic membrane, the three ossicles (incus, malleus, and stapes), and lastly the oval window. This part of the ear is where acoustic energy gets turned into mechanical energy. The tympanic membrane vibrates as acoustic waves hit it, sending the three small bones to hit against one another, pushing the stapes against the oval window. This friction brings amplification to the sounds while also moving it further down the auditory pathway to the inner ear system.

The Inner Ear

The anatomy of the inner ear is made up of the cochlea, semi-circular canals, vestibular nerve, and auditory nerve. In this section of the ear, sound is transformed from mechanical energy to hydraulic energy. This is because the stapes of the inner ear pushes up against the oval window, pushing the liquid inside of the cochlea to create a wave. The cochlea is full of hair fibers that are organized from high frequency to low frequency. This means that when the sound wave hits the section of the cochlea that is responsible for telling the brain what frequency is hit, it breaks through another membrane and sends the signal down the auditory nerve to the brainstem.

Outer Ear Disorders

Anotia

Pinna, or external ear is completely missing. This causes a loss in hearing because the pinna helps direct sound into the ear canal.

Microtia

Pinna is small or disformed.

Atresia

Part or all of the ear canal is not formed.

Stenosis

Narrowing of the ear canal. Can start at a normal size and grow smaller and smaller as the canal gets closer to the tympanic membrane.

Cerumen Buildup

Large build up of ear wax, not super worrisome unless it compacts and affects hearing.

Foreign Body

Outside object lodged into the ear canal. This could be a bug, little toys, or pieces of machinery from a work place.

External Otitis

"Swimmers Ear" or bacterial infection of ear canal. Caused by leftover water within the ear canal that did not drain. This causes bacteria or fungi to grow within the ear canal.

Exostosis

Bony growth in the ear canal, typically benign and grows slowly. This is usually caused by continuous exposure to the cold ocean waters.

Middle Ear Disorders

Tympanic Perforation

This is when there is a hole in the ear drum. Causes of this could be from chemicals, punctures, or forceful amounts of pressure. Usually heal on their own.

Tympanosclerosis

When scar tissue builds up on the ear drum as a result of repeated infections. This does not stop the ear drum from moving typically.

Otitis Media (OM)

A middle ear infection most common cause of conductive hearing loss. Seen more so in children than adults.

Cholesteotoma

A growth within the middle ear space, usually not cancerous or life threatening. Can cause conductive loss and eat away at the ossicle bones, which leads to permanent hearing loss.

Otosclerosis

Formation of a new bone growth around the footplate of the stapes. Soft and spongy bone and as it progresses, the bone beings to harden. Causes conductive hearing loss.

Glomus Tumor

A vascular tumor growing off blood vessels in the middle ear space. Patients can develop tinnitus (or ringing in the ear). Needs to be surgically removed.

Inner Ear Disorders

Bacterial and viral infections are a large cause of hearing loss and disorders within the inner ear. Some of the infections that arise are herpes, syphilis, measles, mumps, rubella, and bacterial meningitis. When bacterial meningitis affects the inner ear, the cochlear hair cells become damaged and the signals that are sent to the brain can become faulty. This type of infection can cause sensorineural hearing loss.

Presbycusis

Hearing loss due to the aging process. Due to long exposures of noise or weakening cartilages.

Noise Induced Hearing Loss

When high level of noise causes damage to the inner ear. Gun shots, attending multiple concerts, or working in construction.

Ototoxicity

Damage to hair cells due to chemical agents or medications (antibiotics, chemotherapy, loop diuretics, analgesics, and antimalarials).

Meniere's Disease

Large build-up of endolymphatic fluid that causes swelling of Reissner's membrane. Can cause vertigo, low frequency sensorineural hearing loss that comes and goes, and extreme tinnitus.

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