The Middle Ear Explained: Eardrum, Ossicles and the Tube That Balances Pressure

Most people think of the ear as one organ, but the part that sits just behind the eardrum is a world of its own. The middle ear is a tiny, air-filled room inside the skull bone. It contains a membrane, a chain of three bones, two very small muscles and the opening of a narrow tube that leads down to the throat. Together they do something engineers would recognise as a translation job: they take the gentle movement of air and turn it into a firmer push that fluid can feel.

What sits inside the middle ear?

The front door of the middle ear is the eardrum, a thin, cone-shaped membrane that closes off the end of the ear canal. It is flexible enough to move in response to even faint sound, yet sealed, so air from outside does not flow straight through.

Attached to the inner face of the eardrum is the first of three bones known together as the ossicles. Their Latin names are the malleus, incus and stapes; in everyday English they are the hammer, anvil and stirrup, after their rough shapes. The stirrup is often described as the smallest bone in the body. Its flat base rests in a small opening into the cochlea called the oval window, so the chain links the eardrum on one side to the inner ear on the other.

Two tiny muscles are also attached to this chain. They tighten in response to very loud sound and stiffen the bones slightly, although the effect is modest and offers no real protection from sudden bangs.

Why can't sound go straight to the inner ear?

The cochlea is filled with fluid, and moving fluid takes more force than moving air. If airborne sound struck the inner ear directly, much of its energy would bounce off the surface, rather like a voice shouted at a swimmer underwater.

The middle ear solves this in two ways. First, the eardrum is much larger than the oval window, so the energy collected over a wide surface is focused onto a small one. Second, the ossicles act as a small lever system. The result is a stronger, more concentrated push at the entrance to the cochlea. Specialists sometimes call this matching the two media, air and fluid, so that sound can cross from one to the other without being lost.

What does the Eustachian tube do?

The Eustachian tube runs from the middle ear down to the back of the nose and throat. Most of the time it stays closed. It opens briefly when you swallow, yawn or chew, letting a little air in or out so that pressure inside the middle ear matches the air outside.

That balance matters because the eardrum moves most freely when the pressure on both of its sides is equal. If the outside pressure changes quickly, as it can when a plane descends or a train enters a tunnel, the drum is pushed or pulled to one side. Sounds become dull, and the ear can feel full or uncomfortable until the tube opens and the pressure settles, often with a small click.

When the tube is swollen, for instance during a heavy cold, it may not open easily. Air in the middle ear is slowly absorbed, the pressure drops and, in some cases, fluid gathers behind the eardrum. The chain of bones then has to move through something thicker than air, and hearing feels muffled.

Because the middle ear is a transmitter, trouble here, such as fluid, a torn eardrum or stiff bones, usually reduces how much sound gets through rather than how clearly the inner ear analyses it. Professionals call this a conductive problem, described in types of hearing loss. Sound can also reach the cochlea through the skull itself, and comparing the two routes helps separate middle-ear from inner-ear problems, as explained in air and bone conduction.

When to see a doctor

A short-lived blocked feeling after a flight that clears by itself is common. It is worth seeing your family doctor or an ENT doctor if an ear stays blocked or dull, if there is ear pain, discharge or fever, if you notice dizziness, or if a cold seems to have left your hearing muffled for longer than you would expect.

This page explains how the middle ear works in general and cannot tell you what is happening in your own ear.

Key takeaways

• The middle ear is an air-filled chamber holding the eardrum, three linked bones and two tiny muscles.
• It focuses airborne vibration into a stronger push so that sound can enter the fluid of the cochlea.
• The Eustachian tube opens when you swallow or yawn and keeps pressure even on both sides of the eardrum.
• Pressure changes, fluid or stiffness in this space usually make sound weaker rather than distorted.

Keep learning: how the ear works places the middle ear in the full journey of sound.