25 inches in diameter. The anterior two-thirds of the ear canal is embedded in the temporal bone. The outer one 3rd of the canal is cartilage. Even though the shape of every ear canal varies, generally the canal forms an elongated shape curve. The ear canal directs the sound waves towards the tympanic membrane. The ear canal resonates sound waves and increases the volume of the tones in the 3000-4000 Hz range. The ear canal maintains the proper conditions of temperature and moisture necessary to retain the elasticity of the tympanic membrane. Glands, which produce cerumen and tiny hairs in the ear canal, providing additional protection against insects and foreign particles from damaging the tympanic membrane.
The middle ear is made up of the tympanic membrane and the cavity, which houses the ossicular chain. The tympanic membrane or tympanum acts as a divider between the outer ear and the middle ear structures. It’s gray-pink in color when healthful and consists of 3 very thin layers of living tissue. The eardrum is very sensitive to sound waves and vibrates back and forth as the sound waves strike it. The eardrum transmits the airborne vibrations from the outer to the middle ear and also assists in the protection of the delicate structures of the middle ear cavity and inner ear.
The middle ear cavity is based on the mastoid process of the temporal bone. The middle ear cavity extends from the tympanic membrane to the interior ear. It’s about two cubic centimeters in volume and is lined with mucous membrane. The middle ear cavity is, in fact, an expansion of the nasopharynx via the eustachian tube. The eustachian tube acts as an air pressure equalizer and ventilating the middle ear. Typically the tube is closed but opens while chewing or swallowing. When the eustachian tube opens, the air pressure between the outer and middle ear is equalized. The transmission of sound throughout the eardrum is optimal when the air pressure is equalized between the outer and middle ear. When the air pressure between the outer and middle ear is unequal, the eardrum is forced outward or inward causing discomfort and the capability of the eardrum to transmit sound is reduced.