Audiology Services

How Hearing Works

The Outer Ear

The part of the outer ear that we see is called the “pinna” or “auricle”. With its grooves and ridges, the pinna 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 is a highly vascularized area. This means that there’s an abundant flow of blood to the ear canal. Wax (cerumen) accumulates in the ear canal and serves as a protective barrier to the skin from bacteria and moisture. Earwax is normal unless it completely blocks the ear canal.

The Middle Ear

The eardrum, or tympanic membrane (TM), divides the outer and middle ear. Although it’s 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 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 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 mechanical vibrations. This bending of the hair cells causes electrical signals to be sent to the brain by way of the auditory nerve. The cochlea is arranged by frequency — much like a piano — and encodes sounds from 20Hz (low pitch) to 20,000Hz (high pitch) in humans.