The middle ear is an air-filled space behind the eardrum that contains a chain of tiny bones called the ossicles (the malleus, incus and stapes). These bones stretch from the eardrum to the cochlea (your hearing organ in the inner ear). When the eardrum vibrates, it causes the ossicles to move backwards and forwards. This movement passes the sound waves through to the inner ear.
The middle ear is also connected to the space at the back of the nose by a small passage called the Eustachian tube. When you swallow, yawn or blow your nose, the Eustachian tube opens and allows air into the middle ear.