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.
In the cochlea, sound waves are transformed into electrical impulses which are sent on to the brain. The brain then translates the impulses into sounds that we know and understand.
What is the cochlea and what is the function of the cochlea? The cochlea resembles a snail shell or a wound-up hose and 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 fibres inside the partition wall are put into motion. There are approximately 24,000 of these hair fibres, arranged in four long rows.
The auditory nerve
What is the auditory nerve? The auditory nerve is a bundle of nerve fibres that carry information between the cochlea in the inner ear and the brain. The function of the auditory nerve is to transmit signals from the inner ear to the brain.
The hair fibres in the cochlea are all connected to the auditory nerve and, depending on the nature of the movements in the cochlear fluid, different hair fibres are put into motion.
When the hair fibres move they send electrical signals to the auditory nerve which is connected to the auditory centre of the brain. In the brain the electrical impulses are translated into sounds which we recognise and understand. As a consequence, these hair fibres are essential to our hearing ability. Should these hair fibres become damaged, then our hearing ability will deteriorate.
The vestibular – the balance mechanism
What is the vestibular? The vestibular is another important part of the inner ear. The vestibular is the organ of equilibrium. The vestibular’s function is to register 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 fibres which react to the movement of the fluid sending little impulses to the brain. The brain then decodes these impulses which are used to help the body keep its balance.