The Ear - One of Our Most Sensitive Organs

   

"Not being able to see isolates you from objects. Not being able to hear isolates you from people."

Immanuel Kant, Philosopher
 
The ear is one of the most sensitive organs in the human body. It converts minimal mechanical pressure fluctuations into electrochemical energy, which it then transmits to the brain as a nerve impulse. It helps to provide early warnings of dangers, enables us to communicate and gives us spatial orientation.

 

Here you can find out more about this evolutionary marvel.

 

 
 
   
 
 
 

 

Caption
1. malleus, 2. incus, 3. stapes, 4. the semicircular canals of the vestibular apparatus, 5. ear canal. 6. eardrum, 7. cochlea, 8. Eustachian tubes 

 
 

The human auditory system serves to perceive pressure fluctuations in the air as tones or noise. Such fluctuations are referred to as sound.

When the eardrum is hit by sound waves, it transmits its movements through the auditory ossicles known as the hammer, anvil and stirrup to the coiled pea-sized spiral cavity in the inner ear called the cochlea, which contains around 25,000 tiny sensory hairs suspended in fluid.

 

These hairs only need to be bent by a distance around the size of a hydrogen atom in order to convert the energy into an electromechanical signal and send this to the brain via the auditory nerves.

 
 
 
 

 
 

The closer the pressure fluctuations are together in terms of time, the higher the tone perceived. The frequency of these fluctuations (fluctuations per second) is measured in hertz (Hz). The human range of hearing lies between 16 Hz and 16,000 Hz, but some animals can hear sounds at frequencies of up to 100,000 Hz!

 

Sound pressure is also a significant factor alongside frequency. The amount of sound pressure is measured in decibels (dB). The higher the number of decibels, the louder the noise. If a sound measurement is given in dB(A), this is an A-weighted value that attempts to represent the volume as it is heard, taking the sensitivity of the human ear into account.

 

The decibel is a logarithmic unit. A difference of 3dB is barely noticeable but means as much as double the sound intensity in a physical sense. A difference of 10dB therefore means ten times the sound intensity, even though we only perceive the sound in question to be twice as loud.

 
 
 
 

 
 

The stronger the sound exposed to, the more likely the sensual hairs are to become damaged. The damage process begins with agglutination and the loss of elasticity and ends with the fine structures breaking off like blades of grass in the wind. According to the latest findings, so-called free radicals are also involved in the damage process.

The hairs in the front area of the ear are responsible for higher frequencies. The fact that these hairs are the first to die off means that hardness of hearing often begins in this high frequency range. No noticeable hearing loss occurs when half of these hairs fall out, meaning that the initial stages of a hardness of hearing are often not identified until it is too late. A hardness of hearing cannot be healed, but can only be counterbalanced by wearing a hearing aid.

 

Alongside sound intensity, the exposure time also plays a significant role in deciding whether noise damage will have a long-term influence on an individual's hearing. The hairs can normally recover up to a certain level of exposure if they are given enough peace and quiet after the sound exposure. The general rule of thumb is that a period of exposure should be followed by at least double the amount of peace and quiet.

 
 
 
 

 
 

Where sound in the workplace is concerned, the German institutions for statutory accident insurance and prevention ("Berufsgenossenschaften") have determined how long people can be exposed to noise during their working days without harmful effects. These values should also be used as an orientation for sound exposure outside of the work environment!

85 decibels (A) - non-hazardous for up to 8 hours
88 decibels (A) - non-hazardous for up to 4 hours
100 decibels (A) -non-hazardous for up to 15 minutes
119 decibels (A) - non-hazardous for up to 1 minute

Extreme impulse noise such as the discharge of a pistol, fireworks in close proximity to the ear or a slap around the ear (> 170 decibels (A)) is highly likely to lead to immediate and lasting damage!

 

 

 

 

Warning: People normally cannot tell when a noise becomes too much for their ears. The initial warning signals such as a deaf feeling, a ringing in the ears and headaches are not reliable and are often ignored. Whatever people may believe, you really cannot get used to noise!

 

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