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What is the inner ear?
What we think of as the “ear” is actually a three-part structure. The outer ear is the part you see and your ear canal. The middle ear is a box-shaped area behind the tympanic membrane (eardrum) that includes the three smallest bones in your body. And the inner ear is just beyond the middle ear, in a small hole in the temporal bones that help make up the sides of your skull.
What does the inner ear do?
Your inner ear has two tasks: Making it possible for you to hear and helping you keep your balance.
Your inner ear is the last stop that sound waves make in a carefully orchestrated journey that starts from your outer ear. These waves travel from your outer ear through your middle ear to your inner ear. In the inner ear, the sound waves are converted into electrical energy, which your hearing nerve delivers to your brain as sound, making it possible for you to hear.
At the same time, your inner ear monitors your movements, alerting your brain to changes so your brain can let your body know what to do to stay balanced.
What are the parts of the inner ear?
Your inner ear has three main parts: your cochlea, semi-circular canals (labyrinth) and your vestibule. Your cochlea supports your hearing and your vestibule and semi-circular canals support your balance.
What is the cochlea?
Your cochlea is filled with fluid and shaped like a snail, tapering from a wide end called the base to a narrow head called the apex. The base is most responsive to high-pitched sounds (like birds chirping) while the apex is most responsive to low-pitched sounds (like a bass drum).
The cochlea is split into three tubes by two thin membranes. One of these membranes — the basilar membrane — is like an elastic wall, on top of which sits the organ of Corti.
In the organ of Corti, there are tiny cells called hair cells. These cells are so small that the approximately 18,000 cells in your cochlea could fit on the head of a pin.
Stereocilia are on top of these hair cells. Stereocilia are delicate, hair-like projections that react to cochlea fluid movement. There are two kinds of hair cells — inner hair cells and outer hair cells. The inner hair cells are most responsive to louder sounds; the outer hair cells are most responsive to softer sounds.
Each hair cell also has a connection to the hearing nerve, but the inner hair cell is most responsible for sending sound through the hearing nerve to the brain. The outer hair cells alert the inner hair cells to softer sounds.
Here’s how the cochlea turns sound waves into sounds:
- Sound enters your outer ear and hits your eardrum (tympanic membrane), which is the wall of your middle ear, causing the tiny middle ear bones (malleus, incus and stapes) to move.
- The stapes is found in the oval window (a small hole) in the cochlea. When it moves, it makes ripples in your cochlea’s fluid.
- This ripple moves the stereocilia like an ocean current moves plants on the sea floor.
- This movement of the stereocilia on the inner and outer hair cells sparks an electrical signal that your auditory nerve carries to your brain’s temporal lobe. The temporal lobe perceives the electrical signal as sound.
What are semi-circular canals?
Semi-circular canals are tubes coiled within your inner ear. Like the cochlea, the canals are filled with liquid and lined with hair cells. Instead of sound waves, these tiny hairs react to body movements. They’re mostly responsible for rotary motion, or motion not in a straight line.
What is the vestibule?
The utricle and saccule in the vestibule are mostly responsible for forward/backward and up/down motion.
Here’s how the vestibular system works:
- When you move your head, the fluid in your semi-circular canals shifts the tiny hairs in the canals.
- This triggers activity in your vestibule, which is connected to your semi-circular canals by sacs, called your saccule and your utricle. Like your semi-circular canals, your saccule and utricle contain fluid and tiny hairs that help them sense movement.
- Your semi-circular canals and your vestibule let your brain know about the movement. Then your brain lets your body know how to stay balanced.
Conditions and Disorders
What common conditions and disorders affect the inner ear?
Your hearing and your sense of balance rely on a healthy inner ear. Several conditions and disorders can affect your inner ear. Some inner ear conditions, such as acoustic neuroma or Ménière disease, can affect your hearing and your sense of balance.
What inner ear conditions affect hearing?
- Sensorineural hearing loss can be caused by aging, disease, loud noises, genetics or some medications. This is the most common kind of hearing loss. It’s often referred to as “nerve deafness,” which isn’t really accurate. This type of hearing loss usually isn’t an issue with the nerve; it’s due to changes in the hair cells and/or stereocilia that send sound to the nerve as an electrical signal. Loud noises are particularly harmful to hearing. Your stereocilia, which detect sound waves, can be damaged or destroyed if you spend time around loud noises without protecting your ears. Once you’ve damaged your hair cells or stereocilia, they can’t be regrown and they can’t be replaced. Hearing aids and hearing assistive devices can help with hearing loss by making sound louder so the remaining hair cells and stereocilia can respond.
- Tinnitus, or ringing in the ears, is often related to hearing loss. It can happen when hair cells have been damaged. You may also experience tinnitus when the brain is trying to replace the sounds it can no longer hear.
What inner ear conditions affect balance?
- Labyrinthitis. Labyrinthitis is inflammation of the inner ear labyrinth or semi-circular canals. Symptoms may include sudden dizziness, tinnitus, and hearing loss.
- Vertigo. Vertigo is a way to describe feeling dizzy or off balance. True vertigo involves a sensation of spinning. It’s a symptom of various conditions but isn’t a condition itself.
- Vestibular neuritis. Vestibular neuritis is inflammation of the vestibulocochlear nerve in your inner ear. It can cause sudden severe vertigo, dizziness, nausea and vomiting. It’s usually treated with medication to help with nausea and dizziness.
- Benign paroxysmal positional vertigo (BPPV). BPPV happens when the crystals in your vestibule move into your semicircular canals and become trapped. When that happens, you might be more sensitive to movement that usually doesn’t bother you, such as rolling over in bed or when looking up towards the ceiling. BPPV can go away on its own, but it may return. The most effective treatment includes physical therapy exercises. Your healthcare provider can tell you how to manage any symptoms you might have.
How do healthcare providers diagnose inner ear problems?
Healthcare providers use several tests to diagnose inner ear problems, particularly problems with balance. Here are a few examples of inner ear tests:
- Vestibular test battery: This includes several different tests that assess how well the vestibular part of your inner ear and eye reflexes are functioning. Testing may include videonystagmography (VNG), vestibular evoked myogenic potentials (VEMPs), rotary chair and video head impulse testing (vHIT). People taking most of these tests will need to wear goggles around their eyes so healthcare providers can monitor eye movement
- Audiometry tests: In this test, which checks hearing, people sit in a sound booth. They respond to soft sounds and repeat words so audiologists can evaluate their ability to hear and understand. This test helps audiologists to discuss the type and degree of hearing loss that people have and how that hearing loss may affect their daily life.
- Auditory brainstem response (ABR) testing: This test involves placing small stickers on people’s foreheads or behind their ears so audiologists can measure how people’s hearing nerve responds to sound.
- Otoacoustic emissions (OAEs): This test evaluates how well your outer hair cells work. It involves playing sounds into your ears and recording the sounds’ echoes.
What are ways to protect my inner ears?
There are several ways to protect your inner ears from hearing loss. Here are a few:
- Turn the volume down, whether you’re watching TV or listening to music — particularly when listening to music with earbuds.
- Use hearing protection devices (such as earplugs and earmuffs) when you can’t avoid loud sounds.
- Protect yourself from loud, noisy activities and places. Stay far away from the loudest sound-producing sources or loudspeakers.
- Take a break from loud noises and sounds.
A note from Cleveland Clinic
Your inner ear is a complicated, delicate and essential part of your body. Every minute of every day, your inner ear turns sound waves into sounds that keep you safe and enrich your life. It also helps you stay balanced. Hearing loss and balance problems can come without warning and can get worse over time. Talk to your healthcare provider as soon as you suspect there might be something wrong with your hearing or balance.
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