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24 September 2014
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Nervous system - Hearing

Sound: Sounds are vibrations

Ear: Divided into your outer, middle and inner ear

Cochlea: Part of your inner ear, where your actual organ of hearing is located

Locating sounds: Sound reaches your two ears at different times, enabling you to locate its source

Ears, nerves and brain

Your ears are your organs of hearing. In order to hear, however, you also need your cochlear nerves to transmit nerve impulses to your brain, which then interpret the sounds coming from the world surrounding you.

Your ear is divided into three parts:

  • Outer ear: your ear flap, or pinna, and your outer ear canal, which ends at your eardrum
  • Middle ear: the cavity between your eardrum and your inner ear. It contains your ossicles, the three smallest bones in your body - the malleus, incus and stapes
  • Inner ear: a maze of bony chambers called the bony labyrinth, including the snail-like cochlea, which is filled with fluid and contains your actual organ of hearing - the organ of Corti

The journey of sound waves

Your ear flap funnels sound waves into your outer ear canal. The waves travel along this passage until they hit your eardrum and cause it to vibrate. As a result, your ossicles start moving. They, in turn, pass on vibrations to a thin layer of tissue at the entrance of your inner ear called the oval window. The movement of the oval window then sets off wave-like motions in the fluid in your cochlea.

Your body's microphone

Your organ of hearing, the spiral organ of Corti, runs through the inside of your cochlea. It consists of thousands of sensory hair cells, attached to a membrane. Tiny sensory hairs emerge from each sensory hair cell and pierce into a second, gel-like membrane above. Whenever the fluids in your cochlea are in motion, the first membrane vibrates and squashes the sensory hairs against the second membrane. The movement of your sensory hairs is then translated into nerve impulses, which travel along your cochlear nerve to your brain.

Locating sounds

Because you have two ears, you are able to locate the source of a sound. If a sound comes from the right, for instance, it will reach your right ear slightly sooner than your left ear. Or it will be slightly louder in your right ear. As a result, you will recognise the sound as coming from your right.

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