The ear has three parts. A) external, B) middle and C) inner.
A) The External Ear
The external ear consists of the auricle and the external ear canal. The auricle serves the purpose of funnelling sound into the middle ear and also provides an anchor for eye-glasses. Any deformity of the auricle also affects facial appearance.
The extenal ear canal conducts sound to the middle ear. Any occlusion of the ear canal by wax, foreign body, infection, etc. reduces sound conduction.
The sound that reaches the middle ear is amplified by the structures of the middle ear before it reaches the inner ear. Refer to the animation below for additional details.
The ear drum transmits sound pressure through the ossicles to the inner ear. The movement in the ear drum is transmitted to the ossicles which in turn transmit their movement to the inner ear. Because the ear drum is much larger than the stapes, the sound energy transmitted is greatly amplified.
The inner ear consists of two parts:
a) The Cochlear
b) The Semicircular Canals
Patients describe the sensation of a loss of balance as being giddy or dizzy. Doctors use the term vertigo to describe a specific type of dizziness which usually involves a spinning sensation in which the head or the environment actually spins around the patient.
We have an inner ear on each side of the head and both continuously send signals to the brain. So our brain continuously receives signals from both inner ears. From these signals, we know where we are in space. Should one of the inner ear send wrong signals, our brain becomes confused and interpret that we are out of balance. If there is a disorder in the inner ear, a wrong signal may be sent to the brain telling the body that it is falling down, our body reacts in the opposite direction to prevent a fall. It is this reaction that makes a dizzy patient fall.
Because the mechanism of dizziness can be confusing, its worthwhile to describe the mechanism in another way ; any disorder of the semicircular canals or fluid circulation can cause spontaneous and inappropriate signals to be sent to the brain, telling the brain that the body is experiencing environmental change of position when in fact nothing is happening. If the brain thinks that the environment and/or the body position is changing, it compensates immediately to prevent a fall - it moves in the opposite direction. This inappropriate quick response results in the patient falling down during a dizzy spell.
In other words, dizziness can be described as a hallucination of motion - the body thinks that there is an environmental motion when in fact there is none. The sensation of dizziness and its consequences is the response of the body to this hallucination.
Hearing loss in the middle ear can result from:
- A perforation of the ear drum
- A break in the continuity of the ossicles
- stiffness of the ossicular chain or fixation of one of the ossicles.
- Fluid inside the middle ear
- Pressure difference between the external and middle ear.
Hearing loss in the inner ear can result from sound transmission being interrupted anywhere along the Cochlear and the Semicircular Canals. This interruption may be
caused by:
• Destruction of those special nerve cells in the cochlear by prolonged loud noise exposure
• Infection
• Head injury
• Pressure by tumor on the eighth cranial nerve
• Congenital absence of the inner ear