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The ear is an advanced and very sensitive organ of the human body. The ear’s function is to transmit and transduce sound to the brain through the parts of the ear: the outer ear, the middle ear and the inner ear.
The major task of the ear is to detect, transmit and transduce sound. Another very important function of the ear is to maintain our sense of balance.
The ear consists of many small parts, but can be divided into three major parts:
1) The outer ear
The outer ear is the external part of the ear, which collects sound waves and directs them into the ear. Read about the anatomy, the outer ear parts and the function of the outer ear.
The pinna is the only visible part of the ear (the auricle) with its special helical shape. It is the first part of the ear that reacts with sound. The function of the pinna is to act as a kind of funnel which assists in directing the sound further into the ear. Without this funnel the sound waves would take a more direct route into the auditory canal. This would be both difficult and wasteful as much of the sound would be lost making it harder to hear and understand the sounds.
The pinna is essential due to the difference in pressure inside and outside the ear. The resistance of the air is higher inside the ear than outside because the air inside the ear is compressed and thus under greater pressure.
In order for the sound waves to enter the ear in the best possible way the resistance must not be too high. This is where the pinna helps by overcoming the difference in pressure inside and outside the ear. The pinna functions as a kind of intermediate link which makes the transition smoother and less brutal allowing more sound to pass into the auditory canal (meatus).
The ear canal – the auditory canal
Once the sound waves have passed the pinna, they move two to three centimetres into the auditory canal before hitting the eardrum, also known as the tympanic membrane. The function of the ear canal is to transmit sound from the pinna to the eardrum.
The eardrum (tympanic membrane), is a membrane at the end of the auditory canal and marks the beginning of the middle ear. The eardrum is extremely sensitive and pressure from sound waves makes the eardrum vibrate. In order to protect the eardrum, the auditory canal is slightly curved making it more difficult for insects, for example, to reach the eardrum. At the same time, earwax (cerumen) in the auditory canal also helps to keep unwanted materials like dirt, dust and insects out of the ear.
2)The middle ear
The middle ear is the part of the ear between the eardrum and the oval window. The middle ear transmits sound from the outer ear to the inner ear. The middle ear consists of three bones: the hammer (malleus), the anvil (incus) and the stirrup (stapes), the oval window, the round window and the Eustrachian tube.
The bones of the middle ear
The eardrum is very thin, measures approximately 8-10 mm in diameter and is stretched by means of small muscles. The pressure from sound waves makes the eardrum vibrate.
The vibrations are transmitted further into the ear via three bones in the middle ear: the hammer (malleus), the anvil (incus) and the stirrup (stapes). These three bones form a kind of bridge, and the stirrup, which is the last bone that sounds reach, is connected to the oval window.
The oval window
The oval window is a membrane covering the entrance to the cochlea in the inner ear. When the eardrum vibrates, the sound waves travel via the hammer and anvil to the stirrup and then on to the oval window.
When the sound waves are transmitted from the eardrum to the oval window, the middle ear is functioning as an acoustic transformer amplifying the sound waves before they move on into the inner ear. The pressure of the sound waves on the oval window is some 20 times higher than on the eardrum.
The pressure is increased due to the difference in size between the relatively large surface of the eardrum and the smaller surface of the oval window. The same principle applies when a person wearing a shoe with a sharp stiletto heel steps on your foot: The small surface of the heel causes much more pain than a flat shoe with a larger surface would.
The round window
The round window in the middle ear vibrates in opposite phase to vibrations entering the inner ear through the oval window. In doing so, it allows fluid in the cochlea to move.
The Eustachian tube
The Eustachian tube is also found in the middle ear, and connects the ear with the rearmost part of the palate. The Eustachian tube’s function is to equalise the air pressure on both sides of the eardrum, ensuring that pressure does not build up in the ear. The tube opens when you swallow, thus equalising the air pressure inside and outside the ear.
3)The inner ear
The inner ear is the innermost part of the ear, which consist of the cochlea, the balance mechanism, the vestibular and the auditory nerve. Read more in this article about the inner ear’s anatomy, how the inner ear functions and the parts of the inner ear.
Once the vibrations of the eardrum have been transmitted to the oval window, the sound waves continue their journey into the inner ear.
The inner ear is a maze of tubes and passages, referred to as the labyrinth. In the labyrinth can be found the vestibular and the cochlea.