The primary anatomical features of the ear are the external ear, middle ear, inner ear, and the mastoid bone.
The External Ear
The outer part of the ear, known as the external auditory canal, is comprised of cartilage covered by thick skin that has hair and produces cerumen, commonly referred to as ear wax. Further inside the canal, the skin starts to thin and covers bone instead of cartilage. The tympanic membrane, also known as the ear drum, is situated at the end of the external auditory canal and divides the external ear from the middle ear.
The Middle Ear
The tympanic cavity of the middle ear lies behind the ear drum. Instead of skin, the cavity is covered by a lining similar to what you would find inside the nose. There are three small bones located inside the middle ear that transfer sound from the tympanic membrane to the cochlea, which is the hearing organ of the inner ear.
The Eustachian tube connects the tympanic cavity to the back of the nose. The purposes of the tube are to permit air to enter behind the tympanic membrane and to allow mucus and fluid to drain from the ear. The middle ear also connects to the cavities within the mastoid bone located behind the ear.
The chorda tympani nerve that provides taste sensation to the front of the tongue and the facial nerve that allows for facial movement both pass through the tympanic cavity on their way to the mouth and face.
The Mastoid Bone
The mastoid bone situated behind the tympanic membrane contains multiple air cells or pockets that connect to the middle ear. These cells have the same thin lining as found inside the middle ear.
Because of their close connection, chronic ear diseases typically affect both the middle ear and the mastoid bone.
The Inner Ear
The inner ear is enclosed by bone and includes organs that facilitate both hearing and balance. The cochlea is the hearing organ and the semicircular canals, utricle, and saccule are the balance organs. The inner ear has two areas, known as the oval window and the round window, that allow communication with the tympanic cavity. The inner ear also contains fluids known as perilymph and endolymph.
Most diseases affecting the inner ear result in both hearing and balance problems. For example, trauma can cause perilymph to leak from the round or oval window, which can lead to balance problems and hearing loss. Meniere’s disease, which causes hearing loss and balance dysfunction, occurs when there is an increase in the pressure of the endolymph of the inner ear.
How the Ear Functions
Sound causes air vibrations that enter the external ear canal and travel to the ear drum. The tympanic membrane vibrates, which also causes the tiny bones of the middle ear to vibrate. This then causes the fluid inside the inner ear to move. The sensory cells of the cochlea then turn the movement into electrical signals that are transmitted via the auditory nerve to the brain to be interpreted.