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Hearing

Hearing / Ear

The ear is an advanced and very sensitive organ of the human body, and the seat of one of our five senses. The function of hearing is converting sound waves to neural impulses that can be perceived by the brain as sound. Another important function of the ear is to maintain the sense of balance for human beings. The ear is divided into three different parts: The outer ear, the middle ear and the inner ear.

The Outer Ear

The only visible part of the ear is the “pinna” (the auricle) which - with its special helical shape - is the first part of the ear that reacts with sound. The pinna acts as a kind of funnel which assists in directing the sound vibrations further into the ear. The shape of the ear canal serves to enhance frequencies that are important for hearing speech.

Without this funnel, the sound waves would take a more direct route into the auditory canal. This would be both difficult and wasteful, and the sound would be harder to hear and understand. Once the sound waves have passed the pinna, they move two to three centimeters into the auditory canal before hitting the eardrum.

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 eardrum (tympanic membrane), which marks the beginning of the middle ear, is extremely sensitive. 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.

In addition to protecting the eardrum, the auditory canal also functions as a natural hearing aid which automatically amplifies low and less penetrating sounds of the human voice. In this way, the ear compensates for some of the weaknesses of the human voice, and makes it easier to hear and understand ordinary conversation.

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 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, we can find the vestibular apparatus and the cochlea.

The Cochlea

In the cochlea, the sound waves are transformed into electrical impulses which are sent to the brain. The brain then translates the impulses into sounds that we know and understand.

The cochlea resembles a snail shell or a wound-up hose. The cochlea is filled with a fluid called perilymph and contains two closely positioned membranes. These membranes form a type of partition wall in the cochlea. However, in order for the fluid to move freely in the cochlea from one side of the partition wall to the other, the wall has a little hole in it (the helicotrema). This hole is necessary, in ensuring that the vibrations from the oval window are transmitted to all the fluid in the cochlea.

When the fluid moves inside the cochlea, thousands of microscopic hair fibers inside the partition wall are put into motion. There are approximately 24,000 of these hair fibers, arranged in four long rows.

The hair fibers are all connected to the auditory nerve and depending on the nature of the movements in the cochlear fluid, different hair fibers are put into motion. When the hair fibers move, they send electrical signals to the auditory nerve which is connected to the auditory center of the brain. In the brain the electrical impulses are translated into sounds which we recognize and understand. As a consequence, these hair fibers are essential to our hearing ability. Should these hair fibers become damaged, then our hearing ability will deteriorate.

In the cochlea, the sound waves are transformed into electrical impulses which are sent to the brain

The Vestibular

Another important part of the inner ear is the organ of equilibrium, the vestibular. The vestibular registers the body's movements, thus ensuring that we can keep our balance. The vestibular consists of three ring-shaped passages, oriented in three different planes. All three passages are filled with fluid that moves in accordance with the body's movements. In addition to the fluid, these passages also contain thousands of hair fibers which react to the movement of the fluid and send little impulses to the brain. The brain then decodes these impulses which are used to help the body keep its balance.

Hearing Loss

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, we can find the vestibular apparatus and the cochlea.

Signs of hearing loss

  • Trouble hearing in noisy public places
  • Difficulty hearing or/and understanding TV or telephone
  • Difficulty understanding words and conversations within a group of people or a crowd
  • Constantly asking others to repeat themselves
  • Often turning heads to one side when listening to sounds
  • Delay in speech and language development in children

Reasons of hearing loss

  • An inherited medical condition (genetic)
  • Sudden exposure to high noise (environmental)
  • Illness or Traumatic injury (circumstantial)
  • Aging process