How you hear
The ear is made up of the outer ear, the middle ear and the inner ear. Find out about the parts of the ear and the role of each part.
Parts of the ear
The ear has three main parts. These parts include the outer ear, the middle ear and the inner ear. Each section is made up of structures that play clear roles in the process of changing sound waves into signals that go to the brain.
The outer ear is made up of the part of the ear that you can see, called the pinna, and the ear canal. The cup-shaped pinna (PIN-uh) picks up sound waves from the environment and sends them into the ear canal.
The middle ear is an air-filled space, called a cavity, that holds a chain of three bones. These bones include:
- The hammer, called the malleus.
- The anvil, called the incus.
- The stirrup, called the stapes.
These bones are separated from the outer ear by the eardrum, called the tympanic membrane, which vibrates when struck by a sound wave.
The middle ear connects to the back of the nose and upper part of the throat by a narrow channel called the auditory tube, also called the eustachian tube. The tube opens and closes at the throat end to keep the pressure the same in the middle ear and in the environment and drain fluids. Equal pressure on both sides of the eardrum is important for the typical vibration of the eardrum.
Bones of the middle ear
The middle ear has three tiny bones in it, including:
- Hammer, called the malleus — attached to the eardrum.
- Anvil, called the incus — in the middle of the chain of bones.
- Stirrup, called the stapes — attached to the membrane-covered opening that connects the middle ear with the inner ear, called the oval window.
The vibration of the eardrum starts a chain of vibrations through the bones. Because of differences in the size, shape and position of the three bones, the force of the vibration goes up by the time it gets to the inner ear. This rise in force is needed to transfer the energy of the sound wave to the fluid of the inner ear.
The inner ear contains a group of interconnected, fluid-filled chambers. The snail-shaped chamber, called the cochlea (KOK-lee-uh), plays a role in hearing. Sound vibrations from the bones of the middle ear transfer to the fluids of the cochlea. Tiny sensors lining the cochlea, called hair cells, change the vibrations into electrical impulses that are sent along the auditory nerve to the brain. This is where the damage and hearing loss first happen that's due to age, noise exposure or medicine.
The other fluid-filled chambers of the inner ear include three tubes called the semicircular canals, called the vestibular labyrinth. Hair cells in the semicircular canals detect the motion of the fluid when you move in any direction. They change the motion into electrical signals that are sent along the vestibular nerve to the brain. This sensory information allows you to keep your sense of balance.
Traveling to the brain
Electrical impulses travel along the auditory nerve and pass through many information-processing centers. Signals from the right ear travel to the auditory cortex, which is in the temporal lobe on the brain's left side. Signals from the left ear travel to the right auditory cortex.
The auditory cortices sort, process, interpret and file information about the sound. The comparison and analysis of all the signals that reach the brain allow you to detect certain sounds and suppress other sounds as background noise.
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