How Hearing Works
Hearing is an amazing thing. Through the complex pieces of machinery we refer to as ‘ears’, the slightest vibrations in the air are eventually turned into the experience of beautiful music, the voice of your loved ones, or (unfortunately!) the cacophony of a construction site.
But how do they work?
The apparatus we use to hear sound can be categorized into three parts. These are commonly referred to as the inner, outer, and middle ear. These parts of the ear work in sequence:
- First, sound waves in the aire are picked up by the outer ear, which acts as a sort of funnel, passing the vibrations through the ear canal and on to the eardrum.
- Next, the eardrum starts to vibrate. Connected to the eardrum are a group of three bones, which also start to vibrate.
- These bones are also connected to the cochlea, or inner ear. This is a spiral-shaped organ that is filled with fluid, which also vibrates when it receives sound. Inside are thousands of tiny hairs, which turn this vibration into electrical signals.
- Auditory nerves transmit these signals to the brain, which interprets them as sound.
Let’s take a closer look.
The Outer Ear
The outer ear is also known as the auricle or pinna. This is what most of us think of when we say “ear” because it is what we can actually see. It is mostly outside the head, thus the name: outer ear.
The funny-shaped ridges that cover the ear act as a natural amplifier which is designed to boost noises ranging from 2000 to 3000 Hz. This is the pitch of human speech, and so ensures that we hear our friends talking above any ambient noise.
Connecting the outer ear to the middle ear is a part called the ear canal. This is a narrow tube with the eardrum at one end. Glands in the ear canal secret a wax which helps to protect the canal from excessive moisture and bacteria. Despite what some people think, this wax is a perfectly normal part of the functioning of the ear. Unless your ears are blocked with wax, it is nothing to worry about!
The Middle Ear
The middle ear starts at the eardrum, which is technically referred to as the ‘tympanic membrane’. The eardrum is extremely thin, so it can pick up even the smallest sound waves, but is also pretty tough.
On the other side of the eardrum are the three tiniest bones in the human body: the ossicles. These are the familiar hammer, anvil, and stirrup. Together, the ossicles act as an amplifier, turning the small vibrations of the eardrum into larger ones, and passing them on to the inner ear.
Another feature of the middle ear, the Eustachian tube, is a small canal that allows the air pressure on both sides of the eardrum to be equalized. When you feel your ears ‘pop’ on an airplane, this is actually the Eustachian tube opening.
The Inner Ear
Lying quite deep inside the skull is the inner ear, which is made up of two parts. The first, the semicircular canals, actually have nothing to do with hearing at all. Rather, they are responsible for your sense of balance.
The other part of the inner ear, the cochlea, takes the vibrations of the ossicles and transforms them into nerve impulses. The cochlea is a strange, snail-shaped spiral which is filled with fluid.
On the inside surface are thousands of tiny hairs, arranged by the frequency of vibration they are sensitive to, just like a piano. They pick up the vibrations in the fluid of the cochlea, turn these into electrical signals, and send them down to the brain.
Finally, in the brain, these electrical signals are interpreted as sound: everything from the bang of a drum to the soothing sound of a waterfall!