The middle ear is located inside an air-filled cavity and smooth walls (as if they are coated with "biological varnish") and located behind the ear drum (tympanic membrane).
Inside the cavity there are three small ear bones: the malleus (or hammer), incus (or anvil), and stapes (or stirrup). One opening of the Eustachian tube is also within the middle ear.
The malleus bone has an elongated part called "the handle of the hummer" (the manubrium, or handle) and is connected to the movable part of the eardrum. The incus is the bridge between the malleus and stapes. The size of the stapes bone is miniature. It is the smallest bone in our body.
The sequence of mechanical events that stands behind the order of the three bones is: (1) Vibration of the tympanic membrane transmits the movement to the malleus. (2) Vibration of the malleus is transferred to the incus. (3) Vibration of the incus causes vibration of the stapes. (4) When the stapes footplate transmits the sound energy to the oval window, it causes wavy movement of fluid within the cochlea (a portion of the inner ear).
The healthy middle ear is filled with atmospheric air. The air of the middle ear have indirect contact with the environmental air outside the body. The Eustachian tube enables air flow to the chamber of the middle ear via the back of the pharynx.
The middle ear is called also the tympanic cavity. It is a cavity in the skull that is ventilated through the nose. The internal part of the mastoid, that is part of the temporal bone (located behind the pinna), also contains atmospheric air, which is ventilated via the middle ear. The resting state of the Eustachian tube is collapsed.
Activity such as swallowing and passive conditions such as positive pressure are associated with opening the tube.
When taking off in a small airplane, the surrounding air pressure goes from higher (on the ground) to lower air pressure high above the ground. Air in the compartment of the middle ear expands as the aircraft goes up. The outcome is that the air is pushed into the back of the nose and mouth.
On the way of the aircraft to the landing area of the air port, the air in the compartment of the middle ear becomes more condensed, and a relative vacuum is produced. Passengers are opening their Eustachian tube intentionally in order to equalize the pressure between the middle ear and the surrounding atmosphere as the plane descends.
A diver who is going down, experiences increase in pressure. Since water are heavier than air, he is under greater rates of pressure change while he goes up or down. Frequent and active opening of the Eustachian tube is required on the way down, where the pressure is higher.
The amazing design of the tympanic membrane and the order of the ossicles enables a good acoustic managing of the sound transmission along the external and middle ear to the cochlea. The 3 known principles that play important part in the mechanic of the middle and internal ear are: (1) the "hydraulic principle". (2) the "lever principle". (3) the "round window protection" principle. Impacted cerumen may block the external ear canal, and can be considered as a cause of acute tinnitus and hearing loss.
Abnormality in the ossicles includes otosclerosis, missing ossicles, or holes in the tympanic membrane. This pathology usually produce conductive hearing loss. Conductive hearing loss may also result from middle ear inflammation, when the air filled space is replaced by fluid.
The surgical procedure for reconstruction of the anatomy of the tympanic membrane and ossicles is called tympanoplasty. Since the surgical technology is changing from decade to decade, it is important to emphasize that we deal with the current practice of autografts and bone prosthesis.
Muscle fascia is used for the tympanic membrane, and polymers are used for the production of artificial ear bones. Some researchers found association of tinnitus, which is one of main 4 symptoms of meniere disease, to otosclerosis and cholesteatoma.