Sound is an essential part of all of our lives.  It allows us to communicate with others via speech, it helps us to sense imminent danger, and it affords us the enjoyment and entertainment of music.  But, how does sound make its way from vibrations in the air to our own auditory perception which we can easily identify and translate? Our bodies are miracles of science, and the answer to that question is fascinating.  

Illustration by Lydia V. Kibiuk, Baltimore, MD; Devon Stuart, Harrisburg, PA

The Outer Ear

Our hearing begins with the collection of sound waves by the pinna (the external ear flap) and the funneling of those waves into the external auditory canal (the part you put a q-tip into to clean).  The pinna extends beyond our head and angles slightly forward in order to more easily catch sounds in front of us and deflect those from behind.  From there, the sound waves hit the tympanic membrane (ear drum), and make it vibrate.  

The Middle Ear

Attached to the ear drum are the three smallest bones in our bodies: the malleus, incus, and stapes—commonly called the “hammer”, “anvil”, and “stirrup” because of their respective shapes. These three bones vibrate in turn, and the stapes (stirrup) pushes against the oval window causing it to vibrate.  The oval window connects the middle ear, which is filled with air, to the inner ear, which is filled with fluid.  

The Inner Ear

The movement of the oval window sets vibrations into motion inside the fluid of the inner ear which then travel into the cochlea, a snail-shaped organ which separates frequencies and sends information about them to the brain.  

The interior of the cochlea is tuned to respond to different frequencies in different areas.  It is covered with hair cells, and each hair cell is topped by a bundle of hairlike stereocilia.  These hairlike bundles are are moved by the vibrations of fluid inside the cochlea and convert this motion into an electrical current which then activate its corresponding nerve ending.  Because each segment of the cochlea senses a different range of frequencies, when a nerve ending is activated by the movement of its stereocilia, it sends a signal about that range of frequencies to the brain.  

The Brain

Once a nerve ending within the inner ear has been activated, it sends its new information as electrical impulses along the VIII cranial nerve (auditory nerve) to the brain.  Once within the brain, the signal is processed in three different ways:

  1. A physical reflex is activated (such as jumping at a loud car horn or turning one’s head when someone begins speaking).
  2. The auditory cortex is activated and we perceive the sound (we realize that someone is speaking to us).
  3. Additional areas of the brain are activated as this sound is recognized, and we begin to interpret its meaning (we interpret what the person is saying to us as an important question and form an answer in response). 

Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body Bartleby.comGray's AnatomyPlate 756 Areas of localization on lateral surface of hemisphere. The motor area in red. Areas of general sensations in blue. The auditory area in green. Visula area is in yellow. The psychic portions are in lighter tints.

The Brain and Music

As mentioned, sound is processed in three specific ways by the brain.  Music, however, fits into a very special category when exploring the effects of sound on the human brain.  Our brains separate music from other everyday sounds such as the washing machine on spin cycle or a car horn outside our window.  To us, music is "organized sound," and not only do we process it in the auditory cortex, but it also activates the regions of the brain pertaining to movement, planning, attention, memory, and emotion. According to neuroscientist Valorie Salimpoor, music also releases dopamine into our systems.  Have you ever used music like a drug?  Sure, if you think about it, we all have.  You can come home after a horrible day, put on your favorite album, and instantly feel relieved, elated, or re-energized.  

In the video below, you can see how different regions in neurologist Oliver Sacks's brain were activated during an fMRI while listening to Beethoven versus Bach (whom he favors greatly). 

Additional Interesting Reading

If you enjoyed this basic information about how the ear works and are interested in a more in depth look at how our brain interacts (correctly or incorrectly) with our ears, you will love Oliver Sacks's book Musicophilia: Tales of Music and the Brain.  In it, he gives thorough case studies of people experiencing sound-related neurological disorders such as "amusia" which makes a symphony sound like the clanging of pots and pans, or patients with Parkinson's disease who cannot move but become animated when music is played, among others.


Main image credit to Gerd Altmann.