I woke up last Wednesday not being able to hear from my right ear. Eventually my hearing went back to normal but it got me thinking about how the ear works.
The ear is split into three parts which are further split into even more parts- is anything simple in biology?
There’s the Outer Ear which partly allows us to locate the source of the sound, like whether the sound is behind us or in front of us. It ‘catches’ the sound and directs it into the middle ear:
- The pinna is where sound is funnelled through into the ear canal is where the vibrations travel to the ear drum/ tympanic membrane.
The Middle Ear transfers sound waves in the air into mechanical pressure which is transferred to the fluids in the inner ear:
- The osscicles: the malleus, incus, stapes. They have the role of amplifying and transferring sound to the inner ear and are attached to the oval window of the cochlea.
- The ossicles can be muted by the contraction of the stapedius muscle which protects from loud sounds but not sharp sounds like a gunshot, a reflex which is less effective in older people, maybe explaining the stereotype of older people having lower tolerance to loud music.
The Inner Ear turns the pressure waves into signals that can be understood by the brain:
- The cochlea is split by a basilar membrane which contains two canals filled with fluid and inside the tubes are tiny hair cells called cilia which pick up the vibrations (apparently, one single musical pitch is received by 10-12 cilia) and poke a 3rd canal called the organ of Corti and convert them into chemical signals. Due to the cochlea’s tapered structure, waveforms travelling down the basilar membrane peak at different points in terms of amplitude according to their frequency. The tapered shape also allows the distance between pitches to match our perception of pitch; there is an equal distance between octaves.
- The auditory nerve receives these chemical signals and sends the information as a nerve impulse to the brain.
- The brain were the nerve impulses are interpreted as as sound.
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