An auditory wonder
Your ears appear to be relatively simple structures. But they are, in fact, only part of the complex auditory system — passageways, vibrating structures, nerves and specialized areas of the brain that work together to gather and interpret sound.
In people with normal hearing, the ears can detect a child's whisper or a crack of thunder, the single call of a songbird or the entire range of instruments in an orchestra.
Take a look at the structures of the auditory system, and discover how it makes sense of the sounds around you.
Three parts of the ear
The ear is made up of three primary parts: the outer ear, middle ear and inner ear. Each section is composed of structures that play distinct roles in the process of converting sound waves into signals that go to the brain.
The outer ear is composed of the visible part of the ear (pinna), the ear canal and the eardrum. The cup-shaped pinna (PIN-uh) gathers sound waves from the environment and directs them into the ear canal. When a sound wave strikes the taut, but somewhat flexible eardrum (tympanic membrane), the eardrum vibrates.
The middle ear is an air-filled cavity that holds a chain of three bones: the hammer, anvil and stirrup. The middle ear is connected to the back of your nose and upper part of your throat by a narrow channel called the auditory tube, or eustachian tube. The tube opens and closes at the throat-end to refresh the air in the middle ear, drain fluids and equalize pressure in the ear. Equal pressure on both sides of the eardrum is important for normal vibration of the eardrum.
Bones of the middle ear
The middle ear contains three tiny bones, including the:
- Hammer (malleus), which is attached to eardrum.
- Anvil (incus), which is in the middle of the chain of bones.
- Stirrup (stapes), which is attached to the oval window, the membrane-covered opening to the inner ear.
The vibration of the eardrum triggers 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 increases by the time it reaches the inner ear. This increase in force is necessary 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-le-uh), plays a role in hearing. Sound vibrations from the bones of the middle ear are transferred to the fluids of the cochlea. Tiny sensors (hair cells) lining the cochlea convert the vibrations into electrical impulses that are transmitted along the auditory nerve to your brain.
The other fluid-filled chambers of the inner ear include three tubes called the semicircular canals (vestibular labyrinth). Hair cells in the semicircular canals detect the motion of the fluids when you move in any direction. They convert the motion into electrical signals that are transmitted along the vestibular nerve to the brain. This sensory information enables you to maintain your sense of balance.
Traveling to the brain
Electrical impulses travel along the auditory nerve and pass through several information-processing centers. Signals from the right ear travel to the auditory cortex located in the temporal lobe on the left side of the brain. 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 the all the signals that reach the brain enable you to detect certain sounds and suppress other sounds as background noise.