How Hearing Works
How hearing works is a highly sophisticated and robust system of the hearing mechanism in the human body. The ear controls hearing and balance and is made up of three parts–the outer, the middle, and the inner ear. All three parts of the ear are important for detecting sound–they work together to move sound from the outer part through the middle, and into the inner part of the ear.
Sound is transformed from pressure waves in the environment to mechanical energy. This is accomplished through a complex system of levels and area ratios. Through electrochemical reactions, this mechanical energy is transformed into something that the brain recognizes as music, warning signals, sounds of nature, and meaningful conversation.
The Outer Ear
The Outer Ear funnels the sounds around us down to the eardrum. The outer ear is made up of the pinna (the ear that you see) and the ear canal. They act as resonators, which amplify certain pitches or frequencies of sound before they reach the eardrum.
The part of the outer ear that we see is the pinna or auricle. The pinna, with its grooves and ridges, provides a natural volume boost for sounds in the 2000 to 3000 Hz frequency range, where we perceive many consonant sounds of speech.
The ear canal, also called the external auditory meatus, is the other important outer ear landmark. The ear canal is lined with only a few layers of skin and fine hair, and it is a highly vascularized area. This means that there is an abundant flow of blood to the ear canal. Ear wax (cerumen) accumulates in the ear canal and serves as a protective barrier for the skin from bacteria and moisture. Ear wax is normal unless it completely blocks the ear canal.
The Middle Ear
The eardrum, or tympanic membrane (TM), is the dividing structure between the outer and middle ear. Although it is an extremely thin membrane, the eardrum is made up of three layers to increase its strength.
The ossicles are the three tiny bones of the middle ear located directly behind the tympanic membrane. These three bones form a connected chain in the middle ear. One of the bones is embedded in the innermost layer of the tympanic membrane, and the third bone is connected to a membranous window of the inner ear. The ossicles take mechanical vibrations received at the tympanic membrane into the inner ear.
The Eustachian tube is the middle ear’s air pressure equalizing system. The middle ear is encased in bone and does not associate with outside air except through the Eustachian tube. This tubular structure is normally closed, but it can be involuntarily opened by swallowing, yawning, or chewing. It can also be intentionally opened to equalize pressure in the ears, such as when flying in an airplane. When this happens, you might hear a soft popping sound.
The Middle Ear is where the sound is changed from pressure waves to mechanical energy. The eardrum (tympanic membrane) is made of layers of skin, which are stretched tight like the top of a drum. As sound enters the ear canal, the eardrum begins vibrating. Attached to the eardrum are three tiny bones called the Hammer (Malleus), Anvil (Incus), and Stirrup (Stapes). Their job is to transfer the vibration of the eardrum to hydraulic waves in the inner ear.
The Inner Ear
The inner ear is an organ located deep within the temporal bone, which is the bone of the skull on both sides of the head above the outer ear. The inner ear has two main structures: the semicircular canals and the cochlea:
- Semicircular Canals. These structures do not contribute to hearing, but they assist in maintaining balance as we move.
- Cochlea. This is the hearing organ of the inner ear, which is a fluid-filled structure that looks like a snail. The cochlea changes the mechanical vibrations from the tympanic membrane and the ossicles into a sequence of electrical impulses. Sensory cells, called hair cells, bend in the cochlea as the fluid is disrupted by the mechanical vibrations. This bending of the hair cells causes electrical signals to be sent to the brain by way of the auditory nerve and up to the brain where they are interpreted as sound. The cochlea is arranged by frequency, much like a piano, and encodes sounds from 20Hz (low pitch) to 20,000Hz (high pitch) in humans.
Sound waves reaching the outer ear cause the eardrum to vibrate. The vibrations are passed on from the middle ear to the inner ear. Fine hair cells in the cochlea play an important role in converting the sound waves into electrical signals.
Check out this video on Hearing and How It Works–it further illustrates how sounds travel from the ear to the brain where they are interpreted and understood.
Protect Your Hearing
Your hearing is a priceless commodity, so take care of it. Here are some things you can do to protect your hearing.
- Turn the Volume Down When Listening to Music or Watching TV
- Avoid Prolonged Exposure to Loud Noises
- Wear Protective Hearing Devices (e.g., Earplugs, Earmuffs) in Noisy Environments
- Get Your Hearing Checked Regularly
- Use a Washcloth to Clean Your Ears (Avoid Using Cotton Swabs)
- See a Professional to Remove Excess or Impacted Earwax
Common Issues That Affect Hearing
There are several things that can affect your hearing, but don’t necessarily cause permanent hearing loss. For example, earwax build-up in the ear canal can reduce sound transmission and your hearing in an ear. The presence of fluid in the eardrum (otitis media) can also cause temporary hearing loss by reducing movement of the eardrum and middle ear hearing bones. These issues are treatable and hearing can readily be restored with proper treatment.
Causes of Hearing Loss
Hearing loss affecting adults is typically associated with aging, but can also be due to hereditary factors, noise exposure (occupational and recreational), viral and bacterial infections, heart conditions or stroke, head injuries, tumors, and certain medications.