How We Hear

We often take our sense of hearing for granted, until something happens to it. In order for our brains to "hear," sounds must travel through our beautifully complex auditory system, which can be divided into four parts:

1. The Outer Ear:

The Outer Ear
The Outer Ear.

This section of the auditory system includes the pinna (that thing you call your "ear" and hang your glasses on) and the outer ear canal. The pinna collects sound waves travelling through the air, and directs them down the ear canal to the eardrum (tympanic membrane). The outer ear canal is lined with tiny hairs, and glands which produce earwax (cerumen). The cerumen helps lubricate the skin in the ear canal, as well as protect the eardrum from foreign debris.

2. The Middle Ear:

The Middle Ear
The Middle Ear.

The eardrum is a membrane which separates the outer and middle ears. The middle ear is an air-filled cavity with a chain of three small bones (the ossicles) suspended in air. The malleus (hammer) is connected to the eardrum, the incus (anvil) is in the middle, and the stapes (stirrup) rests in an opening into the inner ear.

3. The Inner Ear:

The Inner Ear
The Inner Ear.

The inner ear has two important sections, one for hearing and one for balance. The hearing section includes the cochlea and the auditory nerves. The cochlea is filled with fluid, membranes, and other cellular structures which work to keep the sounds moving toward the brain, its final destination!

4. The Brain:

The central auditory system is a neural network which allows your brain to "decode" the sound signals into something meaningful. The processing in this complex "neural highway" helps us to understand speech in background noise and localize sounds.

 

How it all works:

When sounds in the air are collected by your pinna, they travel down the ear canal, causing your eardrum to vibrate. This vibration causes the ossicular chain in the middle ear to move. The stapes in the middle ear rocks back and forth with the vibration, which sets the inner ear fluid into motion. The fluid waves stimulate many tiny hair cells in the inner ear to release a chemical (neurotransmitter), which then tells a corresponding nerve to fire. The chain reaction of firing nerves carries the electrical signals to the brain where they can be decoded into meaningful sound, such as music, birds chirping, or speech.

Many things can go wrong with this highly complex system, resulting in a loss of audibility and/or clarity, increased distortion, sensitivity to loud sounds, as well as perception of sounds that originate internally (tinnitus).