How we hear

See inside the vital organs that help us to communicate and make sense of our surroundings

Our ears are always alert. Whether we are relying on them to relay the sounds of verbal conversations or placing devices into them to listen to music, these organs have the power to enhance our lives. Hearing not only brings us joy through the pleasant sounds of our favourite melodies and the calming noises of nature, it also serves as a life-saving function. When danger approaches, our ears can act as first responders, detecting the sound of footsteps behind us, speeding cars or the warning of a fire alarm. The ability to hear these sounds means we can sense things from more than one direction at a time – something our eyes alone cannot achieve. As the human body has evolved, we have become more responsive to sounds that might indicate danger. Sounds of a higher frequency are amplified in our ears, making us more likely to react. This is also the reason so many of us dislike certain noises, such as nails scratching a chalkboard. Research shows that this sound is in the same frequency range as a human scream or a crying baby. An urgent response to these noises has proven beneficial to our species when attending to someone in danger. People are born with different levels of hearing. However, our increased knowledge of how our ears function has allowed us to create technology that improves some people’s ability to hear. Hearing aids are equipped with microphones that, when attached to ears, can amplify the sound that reaches them. For more severe hearing loss, cochlear implants can be embedded inside the ear. This implant takes on the work of the cochlear by converting any sound detected into electrical impulses for the brain to process.

Young children are more sensitive to loud noises because their ear canals are smaller

2 Reaching the eardrum 3 Vibrating bones 7 Sending signals 6 Detecting pitch 5 Creating signals When a sound hits the eardrum, it causes this thin membrane to vibrate. As the eardrum vibrates, it causes this set of three bones to move and amplify the sound waves. 4 Cochlea receival “Sounds of a higher frequency are amplified in our ears” The cochlea is the size of a pea, and is filled with fluid. The third of the three bones, called the stapes, is in contact with the cochlea. As this bone moves, it causes the liquid inside the cochlea to form rippling waves. The hair cells at the top of the cochlea detect lower pitch sounds, while the hair cells at the bottom are adapted to high-pitched noises. On the inside surface of the cochlea are bundles of hair-like structures called stereocilia. These are moved side to side by the surrounding liquid. Kinetic energy is turned into electrical signals by the hair bundles. The electrical signals are passed along the auditory nerve, which connects the cochlea to the brain. The brain then translates these signals into sounds we can understand.