The middle ear
The middle ear consists of the structures enclosed in the space directly behind the eardrum. There are three bones (ossicles) in the middle ear: the malleus (hammer) is attached directly to the eardrum; the incus (anvil) is attached to the malleus; and the stapes (stirrup) is attached to the incus and to the oval window (which is a membrane not dissimilar from the eardrum). The purpose of this chain of bones, or ossicular chain, is to transmit the movements, the eardrum makes as sound strikes it, to the oval window. It is more sophisticated than just a chain linking two structures, however, the ossicular chain acts like a lever; it takes relatively large movements of the eardrum, and translates them into very small movements at the oval window. The ossicular chain also takes relatively weak movements of the eardrum, and translates them into more powerful movements at the oval window. The ossicular chain is made up of the smallest bones in the human body, the stapes. It is only 2.5 to 3.3 mm long and weighs only 1.9 to 4.3 milligrams.)

The middle ear is also the site of the two smallest muscles in the human body, the stapedius muscle and the tensor tympani muscle. The muscles attach to the bones of the ossicular chain, and to the wall of the middle ear space. These muscles contract and hold the ossicular chain relatively rigid any time a noise of high intensity occurs; the primary purpose of the muscles would appear to be to protect the more delicate inner ear from very loud noises generated within our head when we sneeze or cough or speak. It is also very possible that these muscles may react to help tune our ear, to make it more sensitive to a specific sound that we are attempting to hear. These muscles are very weak and tire easily, so they are only able to provide short periods of protection to the auditory system.

The middle ear contains the Eustachian tube. This is the tube that goes from behind the eardrum down into the back of the nose and throat. This tube has two purposes: one is to allow air to enter the normally closed middle ear space, so that the air pressure on both sides of the eardrum is identical. This tube opens to allow air pressure equalization about every third time we yawn, or chew, or swallow. The other purpose is to allow any fluid that accumulates in the middle ear (which is lined with mucus membrane) to drain down the throat.