How We Hear: The Journey of Sound to the Brain

March 29, 2017 |

The Auditory System

The auditory system is comprised of very delicate, complex structures that work together seamlessly to send a message to the brain. It can be split into three sections: the outer, middle, and inner ear. Beyond the inner ear is the central auditory system, where sound is sent to the brain for processing. Dysfunction of any part of the auditory system can distort, muffle, or block sound completely. The three parts of the ear are detailed below.
Photo credit: American Speech Language-Hearing Association

Outer ear

The outer ear consists of the pinna, external auditory canal, and the tympanic membrane (otherwise known as the eardrum). Sound waves are reflected off the pinna and directed into the ear canal (external auditory meatus). Once in the ear canal, the sound waves resonate on the canal walls and vibrate the eardrum.

Middle ear

The middle ear consists of three tiny bones (the ossicles) and two thin muscles (tensor tympani and stapedius) that support the ossicles. The middle ear space is an air filled cavity with a thin tube that runs into the nasopharynx. The Eustachian tube is responsible for equalizing the pressure in the middle ear compared to the environment. Above the opening of the Eustachian tube, suspended in the middle ear space, are the ossicles. The ossicles are the smallest bones in the human body. They are responsible for transferring sound from the outer to the inner ear. Collectively the middle ear bones are referred to as the ossicular chain, which includes the malleus, incus, and the stapes. The malleus is attached to the back of the eardrum. As sound waves vibrate the eardrum, the vibrations travel down the ossicular chain, into the inner ear.

Photo credit: Outlander Anatomy

Inner ear

As mechanical energy transfers down the ossicles, the footplate of the stapes pushes into the oval window of the cochlea. The cochlea is a snail shaped organ that is encased in bone and filled with fluid. As the oval window is pushed in, the fluid inside is displaced, and delicate hair cells are activated. The hair cells then send the message to the auditory nerve.

Central auditory system

The central auditory system starts at the auditory nerve and leads up through the brainstem into the temporal lobe, where sound is processed.

The video below gives a more detailed look at how sound travels through the inner ear:

If you have any questions about your hearing, don’t hesitate to call our audiology team!


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