Saturday, September 23, 2006

What can Affect Hearing Process

I will explain here a hearing process and what can affect it.

Sound waves come through ear canal, reach eardrum and swing it. Vibrations are carried via three hearing bones (in the middle ear) toward the cohlea and causes the liquid within to oscillate. This stimulates hearing receptors. At this point mechanical vibration is converted in nerve excitation which propagates via auditory nerve through brainstem and reaches the brain. Excitation of brain cells in auditory area is recognised by a person as a sond.

**At all this points a sound can be impaired by objective and subjective causes**.

Objective causes:
A foreign body, injury, infection... in ear canal.
Broken eardrum..
Inflammed inner ear, changed pressure in Eustahian tube (diving, changing altitude fast, also at throat inflamation).
Impairment of inner ear.
Any procees which press on auditory nerve on his path toward the brain (tumors, injuries, bleading, ...).
Changes within the auditory nerve: inflammation, sclerosis multiplex, nerve impairment due to lack of vit B ).
Vascular (aneurysm) or blood disturbance (thrombosis, policythemia).

Subjective causes:
Psychic tension, Pain...
Tension can cause the muscles in the middle ear to contract, which can objectively affect the perception of loudness.

All these causes can not only prevent hearing but can also distort a sound or can pruduce tinnitus.