Take a moment to tap on your keyboard, hum a little tune, and continue listening to the sound of my voice. That’s a lot of sound coming in at once, yet we can take in all this information pretty clearly. Hearing is a fascinating process that requires a massive amount of tiny, tiny cells throughout the ear and in the brain. Even the part of the brain that controls hearing is small, yet it activates as we listen to music, have phone conversations, and take in all the sounds around us.
Curious about how the brain controls hearing? You’re in the right place.
What Part of the Brain Controls Hearing?
Sound is processed in the auditory cortex. It receives electrical signals from the Organ of Corti in the inner ear. From the moment a sound is made to the moment it reaches the auditory cortex, it moves through many parts of the ear and is converted from vibration to electrical signal.
That’s right - I said many parts of the ear. Our ears are actually quite a complicated structure, and they do more than just hear sounds! That’s right. Keep reading for a look into the three main parts of the ear, and how they help us hear and do much more.
What Is Sound?
All of the sounds in the world, from a baby’s cry to the tapping of your fingers on the keyboard, is vibration. The movement of vocal cords or the contact made against keys causes the art particles to vibrate and create sound waves.
The frequency of the waves affects the pitch of the resulting sound, while the amplitude of the waves affects the volume and how far it travels.
The hearing process starts to take place when our ears pick up on those sound waves. Our ears are divided into three parts, with only the outer part of the ear readily visible. (This is what you would draw if you were told to draw an ear.) Like a vacuum of sorts, the outer ear directs incoming sound waves into the auditory canal. From there, the waves make their way to the eardrum.
The Eardrum and Middle Ear
Why is the eardrum called the eardrum? Well, this part of the ear actually does function like a drum. The sound waves hit the eardrum, also known as the tympanic membrane, and cause small bones behind it to vibrate. The middle ear (tympanic cavity) picks up on these vibrations, and the process continues.
Have you ever heard a tympani in an orchestra? The tympani is a big, booming kettledrum that stands on its own up to a drummer’s waist. The tympanic cavity’s role in the hearing process is to focus and amplify the sound waves that the tympanic membrane collects so that the inner ear can process them appropriately.
Another “tympani” worth noting in this process is the tensor tympani muscle. The tensor tympani muscle attaches to the malleus, one of the bones behind the eardrum. (The “malleus” bone is named as such because it looks like a hammer!) When flexed, the tensor tympani muscle dampens certain sounds in the ear. This is why you don’t hear the sound of your own chewing and loud sounds nearby don’t immediately harm your ears. Thanks, tensor tympani muscle!
What Happens in the Inner Ear?
The vibration of bones in the middle ear amplifies sound in a way that it can push through to the fluidic inner ear. Here is where the complicated work starts to take place.
If you have read about how the brain processes vision, you know that photoreceptor cells in the eye convert light into electrical signals. Those signals travel through the brain to the visual cortex to communicate what we are seeing. A similar conversion process happens in the inner ear, but not through the use of photoreceptor cells.
Within the inner ear are two structures that are important to mention: the cochlea and the Organ of Corti. The Organ of Corti is a long organ containing sensory receptors. It sits on top of the basilar membrane in the cochlea, which is tasked with reading the vibrations that come from the middle ear. (The membrane contains over 20,000 fibers that pick up sounds based on their frequency. Can you imagine 20,000 of anything on the inside of your ear?)
As the fibers move, they trigger the Organ of Corti’s sensory cells to convert the vibrations into electrical impulses. Now they are ready to reach the brain and tell us what we’re hearing around us.
All this work and we haven’t even left the ear yet!
How Sound Travels Through the Brain
Electrical signals containing information about sounds travel from the Organ of Corti through the cochlear nerve to the auditory canal and cortex. The auditory cortex is located in the temporal lobe; more specifically, the superior temporal gyrus. On a map, it is right in the middle of the brain. This small area has a big role to do: interpret the electrical signals it receives and respond accordingly.
As this process takes place, echoic memory (or sensory memories and information that has to do with sound) is placed in your working memory. Echoic memories are actually stored in the brain for a longer period of time than, say, memories of what you just read or saw. This is because you can only hear something once.
Part of how you recognize sounds within your working memory is by pulling up past memories. If you can connect the electrical signals that were created at the sound of a cat’s meow to memories of other cats, you’re going to quickly recognize what you hear and maybe respond by wondering what your cat wants from you this time.
What Does a Cochlear Implant Do?
The term “cochlea” often brings up memories of the term “cochlear implant,” a device that is used to store hearing abilities. Now that you know a little bit more about hearing, you can have a better understanding of what a cochlear implant does.
Cochlear implants are designed to sit inside and outside the ear. The outside contains a microphone that picks up sound waves just like the outer ear would. Inside, a wire sends signals picked up from the microphone to stimulate the cochlea.
Does this restore hearing completely? Not exactly. Deafness may be caused by damage to the cochlea. It may also occur when the three bones behind the eardrum are unable to do their jobs properly. Brain damage may also lead to hearing loss. Deafness is not just caused by one thing, and it cannot be immediately solved by installing a cochlear implant. (These devices are actually considered controversial to some people in the Deaf community, who view their hearing loss not as a disability, but as a distinct trait that makes them a minority.) Even if the cochlear implant works in a way that the brain can pick up electrical signals, training must be done to help the person who wears the implant recognize those signals.
Did You Know Your Ear Has Another Role?
The inner ear certainly plays a role in sound and hearing, but it also has an additional role: maintaining your equilibrium. An entire system known as the vestibular system works to help you understand which way is up and which way is down so that you can achieve proper balance.
Well, that was certainly an earful! Now that you know what part of the body and brain controls hearing, and how that part of the brain also contributes to balance, you might just be more appreciative of your ears!