How We Hear
Hearing is one of our five senses. It is a process of picking up sound and attaching meaning to sound. The ear is fully developed at birth and infants are able to respond to very faint sounds, as well as very loud sounds.
The ear is divided into three parts prior to sending information to the brain. This includes the outer ear, the middle ear and the inner ear.
- The outer ear includes the pinna, ear canal and eardrum. The pinna is the part of the ear that we see and serves to collect and localize sound vibrations and guide the vibrations to the ear canal. Sound then travels through the ear canal, hits the eardrum and then causes the eardrum to move.
- The middle ear is an air filled space that includes three very small bones (the malleus, incus & stapes) that are connected to each other and are collectively attached at one end to the eardrum and at the other end to the inner ear. The movement of the eardrum causes the bones to vibrate which then causes movement in the inner ear.
- The inner ear includes two functionally separate sections, the cochlea is the hearing section and the semicircular canals are the vestibular or balance part. The balance portion serves to help with the sense of acceleration/deceleration of both rotational and linear motion. The cochlea is a fluid filled bony coiled canal, which is shaped like a snail. The movement of the fluid in the cochlea causes the movement of tiny hair cells, cilia, in the cochlea. These hair cells respond to specific sound pitches and through their movement send electrical signals through the hearing nerve, auditory nerve, to the brain.
The auditory processing centers of the brain then use the electrical signals to interpret the meaning of sound.
Types of Hearing Loss
Hearing loss can occur at any age. It may be caused by many different factors and is categorized by the part of the auditory system that is damaged. Please review “How We Hear” prior to reading this section. It is important to understand the basic anatomy of the ear prior to trying to understand the types of hearing loss. The three basic hearing loss types are: sensorineural hearing loss, conductive hearing loss, and mixed hearing loss.
Sensorineural Hearing Loss
Sensorineural hearing loss involves damage to the inner ear, the cochlea, or to the actual auditory nerve pathways to the brain. It is the most common type of hearing loss, involving about 90% of all people with hearing impairment. This type of loss is often called “nerve deafness” though most causes of hearing loss involve the inner ear and not the hearing nerve. This type of hearing loss is usually not medically or surgically treatable. Most people will benefit from the use of hearing aids with a sensorineural hearing loss and some individuals, with very severe hearing loss, may be helped by a cochlear implant.
Conductive Hearing Loss
Conductive hearing loss involves damage to the outer ear or the middle ear. This type of loss involves a reduction in the volume of sound that is transferred to the inner ear. Conductive loss is often treatable medically or surgically. Common causes of conductive hearing loss are fluid blockage in the middle ear or wax obstructing the ear canal. This is the most common type of hearing loss for children.
Mixed Hearing Loss
Mixed hearing loss is a combination of both sensorineural hearing loss and conductive hearing loss.