The Outer Ear consists of the pinna, the ear canal and the eardrum. The eardrum or tympanic membrane is the boundary between the outer and middle ears.

 

The Middle Ear consists of an air-filled cavity containing a chain of three little bones. These bones are called the malleus, incus and stapes, and transmit sound vibrations from the eardrum to the inner ear, connecting with the inner ear at the oval window. A small passage called the Eustachian tube connects the air-filled middle ear cavity with the back of the throat. The function of the Eustachian tube is to equalize the air pressure in the middle ear to that outside the ear.

The Inner Ear consists of the cochlea or shell-shaped bony spiral filled with special fluids and lined with tiny hair cells that connect to nerve endings. These nerve endings connect to the hearing (auditory) nerve that transmits sound messages to the brain. The organ of balance is also connected to the inner ear.

Sound waves travel along the ear canal and cause the eardrum to vibrate, in the same way as a normal drum. The movement of the eardrum causes the little bones in the middle ear to vibrate, and these vibrate the oval window. This enables sound to be transmitted to the cochlea in the inner ear, which in turn sets the cochlea fluid in motion.

The tiny hair cells in the cochlea respond by creating electrical signals. These are carried along the hearing nerve to the brain, where they are processed and interpreted as sound.

High pitched sounds are detected by the hair cells at the first turn of the cochlea, and low pitched sounds towards the last turn (apex) of the cochlea.

The central auditory system is an network of neural pathways in the brain that is responsible for sensation and interpretation of sound characteristics such as pitch and rhythm as well as sound localization, speech understanding in noisy listening situations and  music perception.

Measuring Hearing

Each sound has a certain pitch or frequency. Frequency is measured in Hertz (Hz). Loudness of a sound, or intensity, is measured in units called decibel (dB).

An audiogram is a graph that helps illustrate usable hearing and the amount of hearing loss for each ear.

On the audiogram, pitch of the sounds is charted from left to right (low to high pitch) by numbers at the top of the grid. Loudness or intensity of the sounds is measured from top to bottom (soft to loud).

The audiologist presents tones one frequency at a time. The softest tone a person can hear at each frequency is marked on the audiogram. This is called a hearing threshold.

Types of Hearing Loss

There are a variety of causes that can lead to hearing loss. Depending on the part of the ear that is affected, we distinguish between three types of hearing loss: conductive hearing loss, sensorineural hearing loss and mixed hearing loss.

Conductive (Middle Ear) Hearing Loss

Conductive hearing loss occurs when there is disruption of sound transmission in the outer or middle ear. It is frequently a temporary condition and can sometimes be corrected or improved with medical or surgical treatment. People with conductive hearing loss notice a reduction in the volume of sound. Hearing aids may be considered if medical or surgical treatment is ineffective.

Sensorineural Loss (Nerve Deafness)

Sensorineural hearing loss occurs when the hair cells lining the cochlea are damaged, resulting in a diminished sound signal being sent to the brain.

               NORMAL              SENSORINEURAL LOSS

Sensorineural hearing loss is usually permanent and does not usually respond to medical or surgical treatment.

As well as noticing a reduction in the volume of sound, people with sensorineural hearing loss may also have a distortion in sound clarity. Recruitment (increased sensitivity to loud sound) can also be present.

Most appropriate management of  sensorineural hearing loss is through fitting of appropriate hearing instruments and an education program that includes strategies designed to assist the person to manage their hearing loss effectively. Assistive listening devices may also be helpful.

Note: People may have a combined conductive and sensorineural  components. This is known as the mixed hearing loss.

Age and Hearing Loss

The popular notion that with age we become "hard of hearing" is often true. Hearing loss occurs gradually in most people as they age. According to The LISTEN HEAR Report on the Economic Impact and Cost of Hearing Loss in Australia, 2006, about 1 out of every 3 Australian adults aged 70 and over has a hearing loss. As many as 1 in every 6 people in Australia suffer from hearing loss...

We are born with a set of sensory cells, and at about age 18 we slowly start to lose them. High noise levels that we are exposed to, disease processes and genetics all contribute to the overall loss and impact over time

Noise Induced Hearing Loss   

Prolonged exposure to loud noise can permanently damage hearing by causing the destruction of hair cells in the cochlea.

Ears should be protected from loud noise whether it be industrial noise from machinery or loud recreational noise from music concerts, firearms, power tools or motors.

Ear muffs and earplugs will provide some protection. Cotton wool will NOT protect ears from the potential risk of damage from noise exposure.