Middle ear

The middle ear is a space behind the eardrum that contains a group of tiny vibrating bones and one end of the eustachian tube.

Most ear infections form in the middle ear. The eustachian tube carries fluid from the middle ear to the throat. Sometimes during a cold, the eustachian tube becomes swollen and fluid is trapped in the middle ear. Bacteria or viruses can grow in this fluid and form an ear infection.