The auditory system enables you to be aware of sound, tone, volume and other auditory-related stimuli. If you “heard it” - your auditory sensory system was responsible for that.
How does the Auditory System work?
Let’s hop a ride on a sound wave and follow it through your auditory system.
You just asked your cousin his age. He answers, “Thirteen.” How did that answer make it from his vocal cords to your understanding of how old he is?
The entrance to your auditory system is through your ear. Thirteen passes through your outer ear on a vibrating wave of air. The vibrating air hits a thin membrane (called the eardrum) stretched over the entrance to your middle ear. Thirteen is transferred from vibrating air into vibration of the eardrum and the other tiny bones that make up your middle ear. The last tiny bone is attached to the membrane of the cochlea, the spiral shaped, fluid-filled organ in your inner ear. The vibration of the membrane starts the liquid of the cochlea vibrating to the tune of Thirteen. At the end of the cochlea is the auditory cranial nerve. The liquid vibrations of Thirteen are transferred into electrical nerve impulses and sent to the brain for interpretation.
Thirteen has arrived at your brain (finally!), but it needs to make some stops in different sections before you can understand what your cousin said.
First the auditory nerve takes the sound signal through the brainstem, where it identifies duration, intensity and frequency.
(Did your cousin whisper “Thirteen” because he’s very shy - or did he shout “THIR-TEEN!” because this is the second time you asked him and he’s ticked off that you didn’t remember? This would be important for you to realize in order to handle your interaction well, right?)
Next it passes through nerve relays that do localization - where the sound came from.
(Did your cousin answer “Thirteen”? Or was it really his father standing a few feet behind him… once he saw that his teenager was being “too cool” to answer your question? Also important to respond properly, right?)
Then it goes through the thalamus, where signals are sent to other sensory systems to prepare your body for a voluntary physical response.
(Is it your cousin’s thirteenth birthday and this question was really just the opening for a hug or a high-five? Now that he’s answered, it’s time: muscles, stand by! Or maybe you’re going to say something in response: get the vocal cords online!)
Next and final stop: the auditory cortex. Here the content of the message is fully decoded, processed and put in context or memory by your brain.
(Your cousin said he was thirteen. Not three and not thirty. Meaning, he’d likely appreciate a CD of his favorite band for his birthday, not a stuffed animal and not a necktie.)
We took our sound on a ride through the primary auditory pathway, but there are non-primary auditory pathways in the brain as well. These pathways are used when your brain receives more than one auditory stimuli at one time in order to prioritize sound signals and process them in order of priority.
(If you’re listening to the news, and your boss calls on the phone, you should probably pay more attention to what he is saying than to the news anchor.)
What happens when it doesn’t work right?
As you followed the sound wave above, you saw several examples of where a malfunction in that part would present a big problem in understanding and communication.
Disorders in the ear section of the auditory sensory system can cause partial or total deafness and inability to hear at certain volumes or frequencies.
Disorders in the brain section of the auditory system can cause inability to understand tone, intensity, meaning and where the sound came from. If the signal routing to primary and non-primary pathways isn’t working right, individuals might have a hard time processing and understanding sounds when there are other auditory or different sensory stimuli they are being exposed to at the same time.
See here for more details on Auditory Processing Disorder, how it manifests and what to do about it.