Functions of the Ear
The two main functions of the ear are:
- assist with our balance, and
- hear the sounds around us.
Although it has been shown that otitis media will have an impact on both of these areas, the main focus of this section is the impact that OM will have on the child’s ability to hear. To help us understand the affect OM may have on our ability to hear, we first need to be familiar with the structure of the ear and how it works.
Structure of the ear
The ear consists of three areas:
- outer ear;
- middle ear, and
- inner ear.
The middle ear is the area we are most interested in when looking at the cause and effects of OM.
The outer ear consists of the pinna, the part you can easily see and feel, and the ear canal. The pinna helps to gather the sound waves around us. These sound waves travel down the ear canal where they strike the ear drum. The ear drum separates the outer and middle ear.
When sound waves strike the ear drum they cause it to vibrate, which in turn causes the three small bones in the middle ear to move. These three small bones are collectively called the ossicles or easily known as the middle ear bones. The ossicles consist of the:
- malleus (hammer);
- incus (anvil), and
- stapes (stirrup).
The stirrup is connected to a tiny membrane on the inner ear called the oval window.
The oval window forms the entrance to the inner ear or cochlea. The cochlea is coiled and filled with fluid. If we magnify a section of the cochlea, we can see that the inner cochlea is lined with tiny hair cells.
How the parts of the ear work together
When the bones in the middle ear move due to sound waves striking the ear drum, the stirrup pushes rhythmically on the oval window. When the oval window moves it causes the inner ear fluid to move and the hair cells to move backwards and forwards. The movement of fluid and hair cells can be likened to the wind in a field of long grass, as the wind blows, the grass sways backwards and forwards. This movement causes electrical impulses to be sent to the brain, which are then converted into the sounds we hear. Anything which interferes with the journey of sound down the ear canal, past the ear drum or through the middle ear, will result in conductive hearing loss.
Role & function of the Eustachian tube
The Eustachian tube allows ventilation of fresh air into the middle ear and drainage of fluids from the middle ear. If we have a cold or flu, have large adenoids or tonsils, or are prone to allergies such as hay fever, the Eustachian tube may become inflamed, swollen or blocked. This will reduce or stop the ventilation and drainage of the middle ear. When this happens it could lead to one of the following three types of otitis media:
- acute otitis;
- chronic otitis (sometime referred to as glue ear), or
- chronic suppurative otitis (better known as runny ear).
For more information about the types of otitis media, visit the Causes, Types and Treatment of Hearing Loss / Otitis Media page.