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What is the Auditory System?

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  • Written By: Sarah Kay Moll
  • Edited By: Heather Bailey
  • Last Modified Date: 28 November 2016
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Sound is transmitted by waves that travel through the air. The auditory system receives these signals and relays them to the brain. Structures in this sensory system take these waves and convert them into electrical signals. These signals are then sent to the auditory parts of the brain.

The auditory system begins at the outer ear, the part of the ear that is visible. Sound waves pass through the outer ear and enter the auditory canal. In the middle ear, these sound waves vibrate the eardrum, which in turn transfers the energy to three small and delicate bones, the malleus, incus, and stapes, sometimes known as the hammer, anvil, and stirrup. This structure of bones serves to amplify and transfer sound waves.

The auditory system transforms vibrations into electrical signals at the inner ear. The inner ear consists of the fluid-filled cochlea, which contains the organ of Corti. The organ of Corti consists of hair cells, cylindrical cells that have thin cilia strands at the top. When a sound wave travels through the cochlea, the cilia strands at the top of the hair cells move back and forth. The inner hair cells transform this energy into electrical signals.

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The auditory nerve carries signals from the organ of Corti to the brainstem, as part of cranial nerve eight, the vestibulocochlear nerve. In the brainstem, the auditory information is processed by the cochlear nuclei and superior olivary complex before it travels up into the midbrain. The three nuclei in this structure, the medial superior olive, the lateral superior olive, and the nucleus of the trapezoid body, are involved in localization of sound. They do this using cues such as differences in the amount of time a sound takes to reach each ear, or the relative intensity of sounds.

The auditory system continues into the midbrain, where the inferior colliculus does higher level processing and integration of auditory information from the previous structures. It also is involved in some localization of sound. From the midbrain, the electrical signals travel to the thalamus, which relays them to the auditory cortex of the brain, located in the temporal lobe.

The auditory system ends at the auditory cortex of the brain. The primary auditory cortex is found on the superior temporal gyrus, which is above the ear on either side of the brain. This cortex can be mapped by the frequency of sound each region processes. Lower frequencies occur closer to the frontal lobe, and higher frequencies occur farther back.

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everetra
Post 5

@Charred - I agree. What’s really amazing is how the central auditory nervous system is used to distinguish noise from meaningful sound. This happens in the brain obviously.

I think it takes training of course. Over time the brain learns to tell the difference between what is meaningful sound from what is not so meaningful.

When my son turns on the loud music, it’s noise to me, but I guess it’s music to his ears. Individual tastes and personality styles play a role, and help shape how the brain filters information in my opinion.

Charred
Post 4

I’ve heard that the best implants for your ear are the cochlear implants. Of course they get their name from the cochlea, in the inner ear. My understanding is that the cochlear implants actually improve hearing function because they are located closer to where the audio signal processing actually takes place.

This is much different than traditional hearing aids, which only amplify existing noise and do nothing to improve hearing. I don’t know if these claims are true but that’s what I’ve heard.

Personally I believe that with advances in technology it will one day be possible to completely cure auditory problems, so that you won’t need implants of any kind.

Mykol
Post 3

If you have ever had inner ear problems, you know how sensitive the auditory system can be. My inner ear problems didn't affect my hearing, but made me very dizzy and off balance.

Once I found out what was wrong, and was able to get this cleared up, the dizziness went away. I find it fascinating how closely related our auditory system is to our balance.

If you have any kind of auditory disorder, it can really make some of your daily activities harder to accomplish. I always remember hearing how intricate our auditory system is.

For those people who are totally deaf, it really affects what you can for a job and how you function day to day.

andee
Post 2

@StarJo - It really is amazing how our bodies work and what an important role each of our senses plays.

It is really easy to take all of this for granted until something stops working quite the way it should be.

I don't understand all the technicalities of how our hearing works, but my dad has to wear a hearing aid because he can't hear out of his ears very well.

I am sure there are technical terms for the way the auditory processing is functioning in his ears, but for him, it was a gradual loss of hearing.

Thankfully they have made some major improvements in these devices over the years. Even though his auditory system is not functioning properly, he can still hear as long as he wears his hearing aid.

StarJo
Post 1

The auditory system is just one good example of how wonderfully and intricately the human body is designed. Every little part of the system has a specific function, and even a small alteration to it could cause the whole thing to fail at receiving sound.

We never really think about what is going on inside our ears while we are interpreting noises. So much happens so fast, yet we get to hear the sounds pretty much as soon as they are made.

The quick response of the auditory system to stimuli reminds me of how quickly our visual system works. As soon as we look at something, our eyes take it in and our brain turns it right-side up so that we can understand what we are seeing. It's just as automatic as our hearing.

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