Parts of the Ear
For the auditory system to function normally, sound has to travel through all 3 parts of the ear: Outer to Middle to Inner.
The Outer Ear
The outer ear is comprised of the pinna at the side of the head, a canal through which sounds travel, and at the end of the canal, the eardrum. The ear canal is curved and irregularly shaped. It is about 2.5 cm in length and about 8 mm in diameter. The curvature of the ear canal prevents the gathering of water and other foreign materials in the canal. The ear canal also keeps the eardrum at a constant temperature and humidity. The outer portion of the ear canal is relatively soft (cartilage), while the inner part is hard and bony. The wall of the soft portion of the ear canal contains glands, which secrete earwax (cerumen). The outer portion (soft) also contains little hairs and the skin cells migrate outwards so as to push out wax, like a self-cleaning mechanism (so NO need to use Q-tips). The ear canal provides ~10 to 15 dB of gain @ 2500-3000 Hz. The ear canal is closed at one end by the eardrum. The outer ear serves to localize, collect, lead and enhance sounds. It also functions as a protective mechanism for the middle ear.
The Middle Ear
Sound pressure waves travel down the ear canal and make their way to the eardrum. When sound makes the eardrum vibrate, the chain of bones behind the eardrum, otherwise known as ossicles, are set into motion, and this induces movement in the cochlea, our organ of hearing.
The eustachian tube: also known as auditory tube or pharyngotympanic tube, links the middle ear and nasopharynx. It is approximately 35 mm long in an adult. Through this tube the pressure of the air in the middle ear cavity is equalized with the atmospheric pressure, permitting free movement of the eardrum. It’s also a passageway for infections to travel from nasalpharynx to middle ear.
The Inner Ear
When the liquid inside of the cochlea is set into motion, it will then set the Basilar Membrane and the hair cells into motion. The stereocilia on top of the hair cells are pushed back and forth. Different hair cells correspond to different sounds with the low frequency sounds placed at the top (apex)of the cochlea and the high frequency sounds at the bottom (base; near oval window). The vibration will thereby convert sound waves into an electrical message that travels to the brain via the auditory nerve.