How Do We Hear

Basics of Hearing

How Hearing Works - Anatomy of ear
Fig 1: Human Ear Anatomy
Hearing works on the sound waves. Sounds (waves) are invisible vibrations that travel through the air. When someone speaks, a mobile phone rings, aeroplane roars to sky or anything else that creates a 'sound', vibrations are sent through the air in all directions.

Practically, all sound waves are unique. That's why each person or thing sounds different and why one person or thing doesn't always sounds the same. Some sound waves might be high pitched or low pitched, loud or soft.

When the sound waves enter our ears, they get converted into messages, which our brains can understand. The brain then interprets those signals into meaningful sounds such as speech. How well the sound waves are captured and how clearly the messages are sent to our brains correlates to how well our ears work.

Anatomy of Ear

Ears are made up of three major parts and functioning of the each part decides on how well we hear.

Outer Ear
Fig 2: Outer Ear

1. Outer ear (the external ear and the ear canal)

The outer ear consists of the auricle (visible part of ear) and the ear canal. Sound is actually just the waves which are transmitted by the air. These sound waves are captured and channelled through the ear canal to the eardrum. The eardrum is a circular membrane which is flexible and vibrates when sound waves strike it.

2. Middle ear (the ear drum and three very small bones)

Middle Ear
Fig 3: Middle Ear
Separated from the outer ear by the eardrum is the middle ear which is an air-filled space. The middle ear consists of three tiny bones: malleus, incus, and stapes (Collectively known as the ossicles), which form a bridge between eardrum and inner ear. The function of ossicles is to vibrate in response to movements of eardrum thereby amplify and relay the sound to the inner ear via the oval window.

3. Inner ear (the cochlea and auditory nerve)

Inner Ear
Fig 4: Inner Ear
The inner ear (or cochlea) is similar to the shape of snail shell, containing several membranes filled with fluids. When the tiny bones in the ear (ossicles) passes sounds to the oval window, the fluid starts to move thereby stimulating the minuscule hearing nerve cells (hair cells) inside the cochlea. These hair cells, via the auditory nerves, send the electrical impulses to the brain where it is interpreted as sound.

How hearing works

  1. Sounds siphons into the ear canal through pinna and causes the eardrum to move. Along the way, the frequencies that we need to understand speech are amplified by resonance.

  2. At the end of the auditory canal, the sound waves reach the eardrum. It vibrates and creates movements of the three ossicles (In order: hammer/ malleus, anvil/ incus and stirrup/stapes). This chain of tiny bones creates a lever effect that mechanically amplifies the weak vibrations of the eardrum.

  3. The footplate of the stapes then transfers the amplified vibrations to the oval window, which is the point of contact with the inner ear, also known as cochlea.

  4. In the fluid filled cochlea, the vibrations are picked up by thousands of hair cells and converted into electrical impulses, which then travel along the auditory nerve to the brain.