Final answer:
The middle ear is an air-filled space that contains the ossicles and connects to the pharynx via the Eustachian tube. It helps amplify sound to the inner ear, which contains fluid necessary for hearing and balance.
Step-by-step explanation:
The middle ear is an air-filled space located within the temporal bone, positioned between the ear canal and the bony labyrinth. It houses the ossicles (malleus, incus, and stapes), which amplify sound waves from the tympanic membrane to the oval window, leading to the inner ear. The Eustachian tube connects the middle ear to the pharynx, helping maintain pressure equilibrium.
During normal circumstances, the middle ear does not contain fluid. However, infections can cause fluid buildup, increasing pressure upon the eardrum from the middle ear. In contrast, the inner ear, which includes structures like the cochlea and vestibule, contains fluid that is essential for the process of hearing and maintaining equilibrium.