How We Hear

Figure 1. Ear anatomy. Ear images on this page courtesy of Sonic Innovations.

The outer ear

Sound first enters our ear at the pinna – the portion of our ear visible on the outside of our head. The pinna collects sound waves and funnels them down the ear canal, to the eardrum. Together the pinna and ear canal are referred to as the outer ear.

The middle ear

The middle ear begins at the tympanic membrane or eardrum. When sound waves from the outer ear strike the tympanic membrane, it vibrates like a drum (hence the term “eardrum”). Behind the eardrum is the middle ear space containing three tiny bones. The eardrum vibrations cause the middle ear bones to vibrate.

Conductive hearing loss

Conductive hearing loss occurs when conduction of sound through the outer ear and/or middle ear is disrupted. Some examples include excessive earwax in the ear canal, perforation of the eardrum (by cotton swabs or other means), and middle ear infection with fluid build up. Approximately 10% of all hearing losses are conductive, which can range from mild to moderate in severity. Conductive hearing loss can often be medically treated, and in many cases, hearing can be restored.

Figure 2. Conductive Hearing Loss.

The inner ear

The cochlea - our hearing and balance organ - together with the auditory (hearing) nerve, are referred to as the inner ear. Sound passes to the inner ear via the vibrations of the middle ear bones, which are connected to the cochlea at one end. Microscopic sensory hair cells within the cochlea convert the vibratory signal into an electro-chemical signal that’s carried by the auditory nerve to the brain, where sound is finally heard and recognized.

Sensorineural hearing loss

Hearing loss that originates in the inner ear is referred to as sensorineural hearing loss or “nerve loss”. Approximately 90% of all hearing losses are sensorineural, most commonly caused by damage to the inner hair cells. Once damaged, hair cells can’t repair themselves nor be medically treated.

In more than 95% of cases of sensorineural hearing loss, hearing aids or cochlear implants are the recommended course of treatment.

Figure 3. Sensorineural Hearing Loss.

Mixed Hearing Loss

Sound can be blocked in multiple places along its path. When a hearing loss occurs from conditions in the inner ear as well as the outer and/or middle ear, this is known as mixed hearing loss.

Figure 4. Mixed hearing loss.