The ear consists of three parts: the outer ear, the middle ear and the inner ear. The middle ear is between the outer ear and the inner ear, and is the main organ for conducting sound. It includes four important parts, including the tympanic chamber, eustachian tube, tympanic sinus and mastoid process, and is one of the air-containing cavities in the human body, with a volume of about 2 ml, each with different physiological functions, of which the tympanic chamber is the main part of the middle ear function. 1. The tympanic cavity – also known as the middle ear cavity – is shaped like an upright matchbox and is located in the middle space between the tympanic membrane and the bottom of the cochlea. It includes the tympanic membrane, the auditory chain and the tympanic muscle. The tympanic membrane is on the outer side of the middle ear and is funnel-shaped, which mainly plays the role of sound transmission and amplification in addition to protecting the middle ear and inner ear; the chain of auditory bones is connected by the hammer bone, anvil bone and stirrup bone in turn, which has the function of sound transmission and amplification in addition to the role of protecting the inner ear; the tympanic chamber muscle is composed of the tympanic membrane tensor and stapedius muscle, which are the two smallest muscles in the body, and mainly plays the role of regulating the process of sound transmission, and due to the interaction of the two muscles, even if Due to the interaction of the two muscles, even if the incoming sound waves are very strong, the vibration can be reduced and the inner ear is protected from sound wave damage. The tympanic membrane is located at the end of the external auditory canal and is concave in shape, normally pearly white. As the tympanic membrane vibrates back and forth causing the auditory chain to move in a piston-like fashion, the surface area of the tympanic membrane is several times larger than that of the stapes footplate where sound energy is amplified and transmitted to the middle ear. The tympanic membrane plays an important role in the transmission of sound, and if the tympanic membrane is perforated for any reason, hearing will be affected. In order for the tympanic membrane to transmit sound effectively, the pressure must be consistent between the inner and outer sides of the tympanic membrane. When the pressure in the middle ear cavity is the same as the change in atmospheric pressure outside the body, the tympanic membrane can function properly. The Eustachian tube connects the middle ear cavity to the oral cavity, and this natural physiological structure serves to balance the internal and external pressures. The eustachian tube is a tube connecting the tympanic cavity and the nasopharynx. It is about 3.5 cm long in adults, and the section near the tympanic cavity is bony and often open. Near the nasal section for the cartilaginous part, can be reduced or expanded, usually closed, when swallowing, chewing, yawning or forcefully blowing the nose to open, so that the pressure inside and outside the tympanic chamber can be regulated, and drainage role. The eustachian tube in children is shorter and straighter than in adults, and its caliber is relatively large, so it is more susceptible to otitis media than adults when the nose or nasopharynx is infected. 3. The tympanic sinus is a small cavity where the mastoid process is connected to the tympanic chamber, and the lid of the tympanic sinus is separated from the inner part of the skull by a cranial concavity. The mucosa of the tympanic sinus is connected to the mucosa of the eustachian tube of the tympanic chamber, which can play a role in draining secretions. 4, mastoid – located below the tympanic chamber, containing different sizes and shapes of air cavity. If there is pain when pressing on the mastoid, it indicates acute inflammation of the mastoid. Because the mastoid air chamber is continuous with the mucosa of the middle ear cavity, when suffering from otitis media for a long time, it is called chronic middle ear mastoiditis.