The part of the outer ear that we see is called 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. This part of the ear is lined with only a few layers of skin and fine hair, with many veins traveling all around it. 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 to the skin from bacteria and moisture. Ear wax is normal, unless it completely blocks the ear canal.
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, called the oval window. The ossicles translate mechanical vibrations received at the eardrum 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 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.
The semicircular canals do not contribute to hearing, but are part of our vestibular system, which helps us maintain balance as we move. The cochlea is the hearing organ of the inner ear, which is a fluid-filled structure that looks like a snail’s shell. The cochlea changes the mechanical vibrations from the eardrum 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. The cochlea is arranged by frequency, much like a piano, and encodes sounds from 20Hz (low pitch) to 20,000Hz (high pitch) in humans.