Hearing and Hearing Loss

ANATOMY OF THE EAR

Outer ear

The external part of the ear (pinna) and the ear canal (external auditory canal) collect sound and direct it inward.

Middle ear
The eardrum (tympanic membrane) and the three small bones (ossicles) convert incoming into vibrations.

Inner EarThe fluid-filled inner ear (cochlea) contains highly sensitive hair cells that move in response to vibrations. The auditory nerve transmits sound information from the hair cells to the hearing center of the brain.

THE PROCESS OF "HEARING"

Sound is transformed into mechanical energy by the tympanic membrane. It is then transmitted through the ossicles to the inner ear where it is changed again into hydraulic energy for transmission through the fluid-filled cochlea. The cochlea’s hair cells are stimulated by the fluid waves and a neurochemical event takes place that excites the nerves of hearing. The physical characteristics of the original sound are preserved at every energy change along the way until this code becomes one the brain can recognize and process.

HEARING LOSS

Hearing loss misleads our brain with a loss of audibility and introduces distortion into the message that reaches the brain. Changes in the effectiveness of the brain to process stimuli, from head trauma, disease, or from aging, can result in symptoms that mimic hearing loss. The ears and the brain combine in a remarkable way to process neural events into the sense of hearing.

TYPES OF HEARING LOSS

Conductive Hearining Loss

Conductive hearing loss is caused by any condition or disease that blocks or impedes the transmission of sound through the middle ear. The result is a reduction in the sound level (loudness) that reaches the cochlea. Generally, the cause of conductive hearing loss can be treated with a complete or partial improvement in hearing. Patients that experience a conductive hearing loss often say that it sounds like they are "plugged up".

Examples of Conductive Hearing Loss:

Obstructed ear canal - excessive/occluding wax, foreign body in the ear canal
Otitis Externa - infection in the ear canal
Middle ear issues - Otitis Media (Infection in the middle ear), fluid in the middle ear, allergies, poor Eustachian tube function, Perforated Eardrum, benign tumors, dislocated ossicles (malleus, incus, or stapes)
Absence or malformed our ear, ear canal, or middle ear

Sensorineural Hearing Loss

A loss or distortion of sound transmission as a result of damage to the inner ear hair cells or any of the pathway from the inner ear to the auditory cortex of the brain is often diagnosed as a sensorineural hearing loss. Sensorineural hearing loss is typically irreversible and permanent. Patients with this type of loss often say that speech sounds muffled, distorted and unclear. The treatment for sensorineural hearing loss is amplification through hearing aids.

Examples of sensorineural Hearing Loss:

Presbycusis - age-related hearing loss with a gradually progressive inability to hear. High frequencies are usually affected first. These individuals may find that speech sounds muffled and unclear and often ask the speaker to speak up & clearly.
Ototoxic Medications - Certain drugs can damage the fidelity of the inner ear system which can lead to either temporary or permanent damage depending on the dosage and the actual drug.
Certain Antibiotics such as aminoglycosides (gentamicin, vancomycin, etc.), erythromycins, and minocycline.
Diuretics
Salicylates
Acoustic Trauma - excessive and prolonged exposure to noise can damage your auditory system
Inner Ear Infections - such as meningitis, herpes, mononucleosis, labyrinthitis, measles, mumps, cytomegalovirus (CMV) can induce hearing loss

Mixed Hearing Loss

If a conductive hearing loss is accompanied by a sensorineural hearing loss, the correct terminology is mixed hearing loss.

Examples of mixed Hearing Loss:

An individual that has presbycusis (age-related hearing loss) develops a middle ear infection, this person's hearing loss will be categorized as a mixed hearing loss.