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HOW THE EAR WORKS

Normal Hearing Function


First, sound waves are transmitted through the air and are intensified by the outer ear and sent down the ear canal to the eardrum.

The sound waves make the eardrum vibrate, which makes three small bones in the middle ear vibrate.

Vibrations from the three bones cause a connected membrane to move fluid in the cochlea.

The waves of fluid in the cochlea cause microscopic hair cells (stereocilia) to flex and bend.

The stereocilia then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted.

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The Outer Ear

The outer ear or Auris externa, is the external part of the ear, which consists of the auricle (pinna) and the ear canal. The Pinna with its folds and grooves provide of natural volume boost for the sounds in the

2 to 3000 Hz frequency range where we hear most of the consonant sounds. It gathers sound energy and focuses it on the eardrum (tympanic membrane)
The tissue walls in the ear canal become thinner as you move towards the interior yet there remains an abundant flow of blood. Earwax (cerumen) accumulates in the ear canal and protects the canal from bacteria and moisture. Earwax is normal unless it completely blocks the ear canal.

 

The Middle Ear

 

The tympanic membrane or eardrum is the dividing membrane between the outer and middle ear. Although it is extremely thin, it's three layers are incredibly strong.
There are three bones in the middle ear that are connected to the eardrum. These three tiny bones (the smallest in the human body) are the Malleus (hammer), Incus (anvil), and Stapes (stirrup). The bones function is to transduce the acoustic energy captured by the eardrum and change it into mechanical energy. The Malleus is connected to the innermost layer of the eardrum and the Stapes is connected to a membrane window in the inner ear, called the oval window. The mechanical energy received at the oval window is then converted into hydraulic energy (fluid movement).
The eustachian tube in the middle ear is a pressure equalization system. The middle ear is completely encased in bone and has no contact with outside air except through the eustachian tube. This structure is normally closed but can be opened by swallowing, yawning or chewing. You can intentionally open it when you equalize the pressure in your ear by holding your nose and blowing.

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The Inner Ear

 

The inner ear is located deep inside the temporal bone. In the inner ear, there are two main systems the auditory system and the vestibular system. The auditory system deals with the processing of sound. The vestibular system deals mainly with balance and orientation.

The main organ of the auditory system is the Cochlea, a fluid-filled structure that looks like a snail shell.

The sound waves have been converted into hydraulic energy. Fluid pulses back and forth through the Cochlea and over tiny hair cells. The waves of fluid in the cochlea cause microscopic hair cells (stereocilia) to flex and bend. The stereocilia then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted. 

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