Hearing loss or decrease are classified in Medicine as either conductive or sensorineural.
The ear has three parts – the outer, middle, and inner ear. Sounds captured by the outer ear travel through the ear canal to the eardrum, a very thin membrane that separates the outer ear to the middle ear.
The middle ear consists of three very tiny bones or ossicles named for their shape: the hammer, anvil, and stirrup. The hammer is attached to the tympanic membrane and the stirrup is attached to the oval window of the inner ear.
Vibrations of the tympanic membrane are amplified and transmitted by the ossicles to the inner ear. There are also two muscles inside the middle ear – the tensor tympani attached to the hammer, and the stapedius muscle which is attached to the stirrup.
In response to loud noise, the stapedius muscle contracts, so that less sound is transmitted to the inner ear. This so-called acoustic reflex is a mechanism that protects the delicate and sensitive inner ear from damage that can be brought about by loud noise.
The inner ear is a delicate and complex structure. It contains the organ of hearing called the cochlea, and the organ of balance called the semicircular canals. The cochlea is shaped like the shell of a snail, is hollow, and it contains a thick fluid and very small cells with hairlike projections that extend to the thick fluid.
Sound transmitted from the ossicles to the inner ear cause vibrations in the fluid and hair cells. The hair cells convert the sound frequencies to nerve impulses that are transmitted to fibers of the nerve involved in hearing, the auditory nerve, which in turn transmits them to the brain.
Conductive hearing loss may be due to structural or mechanical defects in the outer or middle ear. Sensorineural hearing loss involves the inner ear or the auditory nerve.
Loud noise can overwhelm the protective effects of the acoustic reflex in the middle ear and can also damage the hair cells in the inner ear. A hair cell once damaged cannot grow again. Thus, continued or repeated exposure to loud noise can cause progressive and irreversible damage and hearing loss.
Ways to protect our ears from loud noise:
Limit exposure to loud noise. Use of headphones to listen to loud music is discouraged.
Listening to a device with earphones that sit on the top of the ear at 60 percent maximum volume should be limited to one hour per day. Listening to the device with the earphones that are included in the device at 70 percent maximum should be limited to less than 4.6 hours per day, and to less than 1.2 hours if the volume is at 80 percent maximum;
Reduce loud noise if possible;
Stay away from sources of loud noise;
Wear ear protectors;
There are ways to measure noise level – download in your smart phone an application that measures decibels, install a computer program, or use a professional grade decibel meter.
Noise is not a particulate matter like common air pollutants such as dust, ash, or soot but in the Philippines, noise is classified as an air pollutant – an emission, an unwanted sound passed from a known source into the atmosphere. Noise pollution due to loud, unwanted sound is thus legally actionable under the 1999 Clean Air Act or Republic Act 8749.
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